mksh man page on DragonFly
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MKSH(1) BSD General Commands Manual MKSH(1)
NAME
mksh, sh — MirBSD Korn shell
SYNOPSIS
mksh [-+abCefhiklmnprUuvXx] [-T [!]tty | -] [-+o option] [-c string | -s
| file [argument ...]]
builtin-name [argument ...]
DESCRIPTION
mksh is a command interpreter intended for both interactive and shell
script use. Its command language is a superset of the sh(C) shell lan‐
guage and largely compatible to the original Korn shell. At times, this
manual page may give scripting advice; while it sometimes does take por‐
table shell scripting or various standards into account all information
is first and foremost presented with mksh in mind and should be taken as
such.
I'm an Android user, so what's mksh?
mksh is a UNIX shell / command interpreter, similar to COMMAND.COM or
CMD.EXE, which has been included with Android Open Source Project for a
while now. Basically, it's a program that runs in a terminal (console
window), takes user input and runs commands or scripts, which it can also
be asked to do by other programs, even in the background. Any privilege
pop-ups you might be encountering are thus not mksh issues but questions
by some other program utilising it.
Invocation
Most builtins can be called directly, for example if a link points from
its name to the shell; not all make sense, have been tested or work at
all though.
The options are as follows:
-c string mksh will execute the command(s) contained in string.
-i Interactive shell. A shell that reads commands from standard
input is “interactive” if this option is used or if both stan‐
dard input and standard error are attached to a tty(4). An
interactive shell has job control enabled, ignores the SIGINT,
SIGQUIT, and SIGTERM signals, and prints prompts before read‐
ing input (see the PS1 and PS2 parameters). It also processes
the ENV parameter or the mkshrc file (see below). For non-
interactive shells, the trackall option is on by default (see
the set command below).
-l Login shell. If the basename the shell is called with (i.e.
argv[0]) starts with ‘-’ or if this option is used, the shell
is assumed to be a login shell; see Startup files below.
-p Privileged shell. A shell is “privileged” if the real user ID
or group ID does not match the effective user ID or group ID
(see getuid(2) and getgid(2)). Clearing the privileged option
causes the shell to set its effective user ID (group ID) to
its real user ID (group ID). For further implications, see
Startup files. If the shell is privileged and this flag is
not explicitly set, the “privileged” option is cleared auto‐
matically after processing the startup files.
-r Restricted shell. A shell is “restricted” if this option is
used. The following restrictions come into effect after the
shell processes any profile and ENV files:
· The cd (and chdir) command is disabled.
· The SHELL, ENV, and PATH parameters cannot be changed.
· Command names can't be specified with absolute or relative
paths.
· The -p option of the built-in command command can't be
used.
· Redirections that create files can't be used (i.e. ‘>’,
‘>|’, ‘>>’, ‘<>’).
-s The shell reads commands from standard input; all non-option
arguments are positional parameters.
-T name Spawn mksh on the tty(4) device given. The paths name,
/dev/ttyCname and /dev/ttyname are attempted in order. Unless
name begins with an exclamation mark (‘!’), this is done in a
subshell and returns immediately. If name is a dash (‘-’),
detach from controlling terminal (daemonise) instead.
In addition to the above, the options described in the set built-in com‐
mand can also be used on the command line: both [-+abCefhkmnuvXx] and
[-+o option] can be used for single letter or long options, respectively.
If neither the -c nor the -s option is specified, the first non-option
argument specifies the name of a file the shell reads commands from. If
there are no non-option arguments, the shell reads commands from the
standard input. The name of the shell (i.e. the contents of $0) is
determined as follows: if the -c option is used and there is a non-option
argument, it is used as the name; if commands are being read from a file,
the file is used as the name; otherwise, the basename the shell was
called with (i.e. argv[0]) is used.
The exit status of the shell is 127 if the command file specified on the
command line could not be opened, or non-zero if a fatal syntax error
occurred during the execution of a script. In the absence of fatal
errors, the exit status is that of the last command executed, or zero, if
no command is executed.
Startup files
For the actual location of these files, see FILES. A login shell pro‐
cesses the system profile first. A privileged shell then processes the
suid profile. A non-privileged login shell processes the user profile
next. A non-privileged interactive shell checks the value of the ENV
parameter after subjecting it to parameter, command, arithmetic and tilde
(‘~’) substitution; if unset or empty, the user mkshrc profile is pro‐
cessed; otherwise, if a file whose name is the substitution result
exists, it is processed; non-existence is silently ignored. A privileged
shell then drops privileges if neither was the -p option given on the
command line nor set during execution of the startup files.
Command syntax
The shell begins parsing its input by removing any backslash-newline com‐
binations, then breaking it into words. Words (which are sequences of
characters) are delimited by unquoted whitespace characters (space, tab,
and newline) or meta-characters (‘<’, ‘>’, ‘|’, ‘;’, ‘(’, ‘)’, and ‘&’).
Aside from delimiting words, spaces and tabs are ignored, while newlines
usually delimit commands. The meta-characters are used in building the
following tokens: ‘<’, ‘<&’, ‘<<’, ‘<<<’, ‘>’, ‘>&’, ‘>>’, ‘&>’, etc. are
used to specify redirections (see Input/output redirection below); ‘|’ is
used to create pipelines; ‘|&’ is used to create co-processes (see
Co-processes below); ‘;’ is used to separate commands; ‘&’ is used to
create asynchronous pipelines; ‘&&’ and ‘||’ are used to specify condi‐
tional execution; ‘;;’, ‘;&’ and ‘;|’ are used in case statements; ‘(( ..
))’ is used in arithmetic expressions; and lastly, ‘( .. )’ is used to
create subshells.
Whitespace and meta-characters can be quoted individually using a back‐
slash (‘\’), or in groups using double (‘"’) or single (“'”) quotes.
Note that the following characters are also treated specially by the
shell and must be quoted if they are to represent themselves: ‘\’, ‘"’,
‘'’, ‘#’, ‘$’, ‘`’, ‘~’, ‘{’, ‘}’, ‘*’, ‘?’, and ‘[’. The first three of
these are the above mentioned quoting characters (see Quoting below);
‘#’, if used at the beginning of a word, introduces a comment – every‐
thing after the ‘#’ up to the nearest newline is ignored; ‘$’ is used to
introduce parameter, command, and arithmetic substitutions (see
Substitution below); ‘`’ introduces an old-style command substitution
(see Substitution below); ‘~’ begins a directory expansion (see Tilde
expansion below); ‘{’ and ‘}’ delimit csh(1)-style alternations (see
Brace expansion below); and finally, ‘*’, ‘?’, and ‘[’ are used in file
name generation (see File name patterns below).
As words and tokens are parsed, the shell builds commands, of which there
are two basic types: simple-commands, typically programmes that are exe‐
cuted, and compound-commands, such as for and if statements, grouping
constructs, and function definitions.
A simple-command consists of some combination of parameter assignments
(see Parameters below), input/output redirections (see Input/output
redirections below), and command words; the only restriction is that
parameter assignments come before any command words. The command words,
if any, define the command that is to be executed and its arguments. The
command may be a shell built-in command, a function, or an external com‐
mand (i.e. a separate executable file that is located using the PATH
parameter; see Command execution below). Note that all command con‐
structs have an exit status: for external commands, this is related to
the status returned by wait(2) (if the command could not be found, the
exit status is 127; if it could not be executed, the exit status is 126);
the exit status of other command constructs (built-in commands, func‐
tions, compound-commands, pipelines, lists, etc.) are all well-defined
and are described where the construct is described. The exit status of a
command consisting only of parameter assignments is that of the last com‐
mand substitution performed during the parameter assignment or 0 if there
were no command substitutions.
Commands can be chained together using the ‘|’ token to form pipelines,
in which the standard output of each command but the last is piped (see
pipe(2)) to the standard input of the following command. The exit status
of a pipeline is that of its last command, unless the pipefail option is
set (see there). All commands of a pipeline are executed in separate
subshells; this is allowed by POSIX but differs from both variants of
AT&T UNIX ksh, where all but the last command were executed in subshells;
see the read builtin's description for implications and workarounds. A
pipeline may be prefixed by the ‘!’ reserved word which causes the exit
status of the pipeline to be logically complemented: if the original sta‐
tus was 0, the complemented status will be 1; if the original status was
not 0, the complemented status will be 0.
Lists of commands can be created by separating pipelines by any of the
following tokens: ‘&&’, ‘||’, ‘&’, ‘|&’, and ‘;’. The first two are for
conditional execution: “cmd1 && cmd2” executes cmd2 only if the exit sta‐
tus of cmd1 is zero; ‘||’ is the opposite – cmd2 is executed only if the
exit status of cmd1 is non-zero. ‘&&’ and ‘||’ have equal precedence
which is higher than that of ‘&’, ‘|&’, and ‘;’, which also have equal
precedence. Note that the ‘&&’ and ‘||’ operators are
"left-associative". For example, both of these commands will print only
"bar":
$ false && echo foo || echo bar
$ true || echo foo && echo bar
The ‘&’ token causes the preceding command to be executed asynchronously;
that is, the shell starts the command but does not wait for it to com‐
plete (the shell does keep track of the status of asynchronous commands;
see Job control below). When an asynchronous command is started when job
control is disabled (i.e. in most scripts), the command is started with
signals SIGINT and SIGQUIT ignored and with input redirected from
/dev/null (however, redirections specified in the asynchronous command
have precedence). The ‘|&’ operator starts a co-process which is a spe‐
cial kind of asynchronous process (see Co-processes below). Note that a
command must follow the ‘&&’ and ‘||’ operators, while it need not follow
‘&’, ‘|&’, or ‘;’. The exit status of a list is that of the last command
executed, with the exception of asynchronous lists, for which the exit
status is 0.
Compound commands are created using the following reserved words. These
words are only recognised if they are unquoted and if they are used as
the first word of a command (i.e. they can't be preceded by parameter
assignments or redirections):
case else function then ! (
do esac if time [[ ((
done fi in until {
elif for select while }
In the following compound command descriptions, command lists (denoted as
list) that are followed by reserved words must end with a semicolon, a
newline, or a (syntactically correct) reserved word. For example, the
following are all valid:
$ { echo foo; echo bar; }
$ { echo foo; echo bar<newline>}
$ { { echo foo; echo bar; } }
This is not valid:
$ { echo foo; echo bar }
(list)
Execute list in a subshell. There is no implicit way to pass envi‐
ronment changes from a subshell back to its parent.
{ list; }
Compound construct; list is executed, but not in a subshell. Note
that ‘{’ and ‘}’ are reserved words, not meta-characters.
case word in [[(] pattern [| pattern] ...) list terminator] ... esac
The case statement attempts to match word against a specified
pattern; the list associated with the first successfully matched
pattern is executed. Patterns used in case statements are the same
as those used for file name patterns except that the restrictions
regarding ‘.’ and ‘/’ are dropped. Note that any unquoted space
before and after a pattern is stripped; any space within a pattern
must be quoted. Both the word and the patterns are subject to
parameter, command, and arithmetic substitution, as well as tilde
substitution.
For historical reasons, open and close braces may be used instead
of in and esac e.g. case $foo { *) echo bar ;; }.
The list terminators are:
‘;;’ Terminate after the list.
‘;&’ Fall through into the next list.
‘;|’ Evaluate the remaining pattern-list tuples.
The exit status of a case statement is that of the executed list;
if no list is executed, the exit status is zero.
for name [in word ...]; do list; done
For each word in the specified word list, the parameter name is set
to the word and list is executed. If in is not used to specify a
word list, the positional parameters ($1, $2, etc.) are used
instead. For historical reasons, open and close braces may be used
instead of do and done e.g. for i; { echo $i; }. The exit status
of a for statement is the last exit status of list; if list is
never executed, the exit status is zero.
if list; then list; [elif list; then list;] ... [else list;] fi
If the exit status of the first list is zero, the second list is
executed; otherwise, the list following the elif, if any, is exe‐
cuted with similar consequences. If all the lists following the if
and elifs fail (i.e. exit with non-zero status), the list following
the else is executed. The exit status of an if statement is that
of non-conditional list that is executed; if no non-conditional
list is executed, the exit status is zero.
select name [in word ...]; do list; done
The select statement provides an automatic method of presenting the
user with a menu and selecting from it. An enumerated list of the
specified word(s) is printed on standard error, followed by a
prompt (PS3: normally ‘#? ’). A number corresponding to one of the
enumerated words is then read from standard input, name is set to
the selected word (or unset if the selection is not valid), REPLY
is set to what was read (leading/trailing space is stripped), and
list is executed. If a blank line (i.e. zero or more IFS octets)
is entered, the menu is reprinted without executing list.
When list completes, the enumerated list is printed if REPLY is
NULL, the prompt is printed, and so on. This process continues
until an end-of-file is read, an interrupt is received, or a break
statement is executed inside the loop. If “in word ...” is omit‐
ted, the positional parameters are used (i.e. $1, $2, etc.). For
historical reasons, open and close braces may be used instead of do
and done e.g. select i; { echo $i; }. The exit status of a select
statement is zero if a break statement is used to exit the loop,
non-zero otherwise.
until list; do list; done
This works like while, except that the body is executed only while
the exit status of the first list is non-zero.
while list; do list; done
A while is a pre-checked loop. Its body is executed as often as
the exit status of the first list is zero. The exit status of a
while statement is the last exit status of the list in the body of
the loop; if the body is not executed, the exit status is zero.
function name { list; }
Defines the function name (see Functions below). Note that redi‐
rections specified after a function definition are performed when‐
ever the function is executed, not when the function definition is
executed.
name() command
Mostly the same as function (see Functions below). Whitespace
(space or tab) after name will be ignored most of the time.
function name() { list; }
The same as name() (bashism). The function keyword is ignored.
time [-p] [pipeline]
The Command execution section describes the time reserved word.
(( expression ))
The arithmetic expression expression is evaluated; equivalent to
“let expression” (see Arithmetic expressions and the let command,
below) in a compound construct.
[[ expression ]]
Similar to the test and [ ... ] commands (described later), with
the following exceptions:
· Field splitting and file name generation are not performed on
arguments.
· The -a (AND) and -o (OR) operators are replaced with ‘&&’ and
‘||’, respectively.
· Operators (e.g. ‘-f’, ‘=’, ‘!’) must be unquoted.
· Parameter, command, and arithmetic substitutions are performed
as expressions are evaluated and lazy expression evaluation is
used for the ‘&&’ and ‘||’ operators. This means that in the
following statement, $(<foo) is evaluated if and only if the
file foo exists and is readable:
$ [[ -r foo && $(<foo) = b*r ]]
· The second operand of the ‘!=’ and ‘=’ expressions are a subset
of patterns (e.g. the comparison [[ foobar = f*r ]] succeeds).
This even works indirectly:
$ bar=foobar; baz='f*r'
$ [[ $bar = $baz ]]; echo $?
$ [[ $bar = "$baz" ]]; echo $?
Perhaps surprisingly, the first comparison succeeds, whereas
the second doesn't. This does not apply to all extglob
metacharacters, currently.
Quoting
Quoting is used to prevent the shell from treating characters or words
specially. There are three methods of quoting. First, ‘\’ quotes the
following character, unless it is at the end of a line, in which case
both the ‘\’ and the newline are stripped. Second, a single quote (“'”)
quotes everything up to the next single quote (this may span lines).
Third, a double quote (‘"’) quotes all characters, except ‘$’, ‘`’ and
‘\’, up to the next unquoted double quote. ‘$’ and ‘`’ inside double
quotes have their usual meaning (i.e. parameter, arithmetic, or command
substitution) except no field splitting is carried out on the results of
double-quoted substitutions. If a ‘\’ inside a double-quoted string is
followed by ‘\’, ‘$’, ‘`’, or ‘"’, it is replaced by the second charac‐
ter; if it is followed by a newline, both the ‘\’ and the newline are
stripped; otherwise, both the ‘\’ and the character following are
unchanged.
If a single-quoted string is preceded by an unquoted ‘$’, C style back‐
slash expansion (see below) is applied (even single quote characters
inside can be escaped and do not terminate the string then); the expanded
result is treated as any other single-quoted string. If a double-quoted
string is preceded by an unquoted ‘$’, the ‘$’ is simply ignored.
Backslash expansion
In places where backslashes are expanded, certain C and AT&T UNIX ksh or
GNU bash style escapes are translated. These include ‘\a’, ‘\b’, ‘\f’,
‘\n’, ‘\r’, ‘\t’, ‘\U########’, ‘\u####’, and ‘\v’. For ‘\U########’ and
‘\u####’, “#” means a hexadecimal digit, of thich there may be none up to
four or eight; these escapes translate a Unicode codepoint to UTF-8.
Furthermore, ‘\E’ and ‘\e’ expand to the escape character.
In the print builtin mode, ‘\"’, ‘\'’, and ‘\?’ are explicitly excluded;
octal sequences must have the none up to three octal digits “#” prefixed
with the digit zero (‘\0###’); hexadecimal sequences ‘\x##’ are limited
to none up to two hexadecimal digits “#”; both octal and hexadecimal
sequences convert to raw octets; ‘\#’, where # is none of the above,
translates to \# (backslashes are retained).
Backslash expansion in the C style mode slightly differs: octal sequences
‘\###’ must have no digit zero prefixing the one up to three octal digits
“#” and yield raw octets; hexadecimal sequences ‘\x#*’ greedily eat up as
many hexadecimal digits “#” as they can and terminate with the first non-
hexadecimal digit; these translate a Unicode codepoint to UTF-8. The
sequence ‘\c#’, where “#” is any octet, translates to Ctrl-# (which basi‐
cally means, ‘\c?’ becomes DEL, everything else is bitwise ANDed with
0x1F). Finally, ‘\#’, where # is none of the above, translates to # (has
the backslash trimmed), even if it is a newline.
Aliases
There are two types of aliases: normal command aliases and tracked
aliases. Command aliases are normally used as a short hand for a long or
often used command. The shell expands command aliases (i.e. substitutes
the alias name for its value) when it reads the first word of a command.
An expanded alias is re-processed to check for more aliases. If a com‐
mand alias ends in a space or tab, the following word is also checked for
alias expansion. The alias expansion process stops when a word that is
not an alias is found, when a quoted word is found, or when an alias word
that is currently being expanded is found. Aliases are specifically an
interactive feature: while they do happen to work in scripts and on the
command line in some cases, aliases are expanded during lexing, so their
use must be in a separate command tree from their definition; otherwise,
the alias will not be found. Noticeably, command lists (separated by
semicolon, in command substitutions also by newline) may be one same
parse tree.
The following command aliases are defined automatically by the shell:
autoload='\typeset -fu'
functions='\typeset -f'
hash='\builtin alias -t'
history='\builtin fc -l'
integer='\typeset -i'
local='\typeset'
login='\exec login'
nameref='\typeset -n'
nohup='nohup '
r='\builtin fc -e -'
type='\builtin whence -v'
Tracked aliases allow the shell to remember where it found a particular
command. The first time the shell does a path search for a command that
is marked as a tracked alias, it saves the full path of the command. The
next time the command is executed, the shell checks the saved path to see
that it is still valid, and if so, avoids repeating the path search.
Tracked aliases can be listed and created using alias -t. Note that
changing the PATH parameter clears the saved paths for all tracked
aliases. If the trackall option is set (i.e. set -o trackall or set -h),
the shell tracks all commands. This option is set automatically for non-
interactive shells. For interactive shells, only the following commands
are automatically tracked: cat(1), cc(1), chmod(1), cp(1), date(1),
ed(1), emacs(1), grep(1), ls(1), make(1), mv(1), pr(1), rm(1), sed(1),
sh(1), vi(1), and who(1).
Substitution
The first step the shell takes in executing a simple-command is to per‐
form substitutions on the words of the command. There are three kinds of
substitution: parameter, command, and arithmetic. Parameter substitu‐
tions, which are described in detail in the next section, take the form
$name or ${...}; command substitutions take the form $(command) or (dep‐
recated) `command` or (executed in the current environment) ${ command;}
and strip trailing newlines; and arithmetic substitutions take the form
$((expression)). Parsing the current-environment command substitution
requires a space, tab or newline after the opening brace and that the
closing brace be recognised as a keyword (i.e. is preceded by a newline
or semicolon). They are also called funsubs (function substitutions) and
behave like functions in that local and return work, and in that exit
terminates the parent shell; shell options are shared.
Another variant of substitution are the valsubs (value substitutions)
${|command;} which are also executed in the current environment, like
funsubs, but share their I/O with the parent; instead, they evaluate to
whatever the, initially empty, expression-local variable REPLY is set to
within the commands.
If a substitution appears outside of double quotes, the results of the
substitution are generally subject to word or field splitting according
to the current value of the IFS parameter. The IFS parameter specifies a
list of octets which are used to break a string up into several words;
any octets from the set space, tab, and newline that appear in the IFS
octets are called “IFS whitespace”. Sequences of one or more IFS white‐
space octets, in combination with zero or one non-IFS whitespace octets,
delimit a field. As a special case, leading and trailing IFS whitespace
is stripped (i.e. no leading or trailing empty field is created by it);
leading or trailing non-IFS whitespace does create an empty field.
Example: If IFS is set to “<space>:”, and VAR is set to
“<space>A<space>:<space><space>B::D”, the substitution for $VAR results
in four fields: ‘A’, ‘B’, ‘’ (an empty field), and ‘D’. Note that if the
IFS parameter is set to the empty string, no field splitting is done; if
it is unset, the default value of space, tab, and newline is used.
Also, note that the field splitting applies only to the immediate result
of the substitution. Using the previous example, the substitution for
$VAR:E results in the fields: ‘A’, ‘B’, ‘’, and ‘D:E’, not ‘A’, ‘B’, ‘’,
‘D’, and ‘E’. This behavior is POSIX compliant, but incompatible with
some other shell implementations which do field splitting on the word
which contained the substitution or use IFS as a general whitespace
delimiter.
The results of substitution are, unless otherwise specified, also subject
to brace expansion and file name expansion (see the relevant sections
below).
A command substitution is replaced by the output generated by the speci‐
fied command which is run in a subshell. For $(command) and ${|command;}
and ${ command;} substitutions, normal quoting rules are used when
command is parsed; however, for the deprecated `command` form, a ‘\’ fol‐
lowed by any of ‘$’, ‘`’, ‘"’ (currently, and violating POSIX), or ‘\’ is
stripped (a ‘\’ followed by any other character is unchanged). As a spe‐
cial case in command substitutions, a command of the form <file is inter‐
preted to mean substitute the contents of file. Note that $(<foo) has
the same effect as $(cat foo).
Note that some shells do not use a recursive parser for command substitu‐
tions, leading to failure for certain constructs; to be portable, use as
workaround ‘x=$(cat) <<"EOF"’ (or the newline-keeping ‘x=<<"EOF"’ exten‐
sion) instead to merely slurp the string. IEEE Std 1003.1 (“POSIX.1”)
recommends to use case statements of the form ‘x=$(case $foo in (bar)
echo $bar ;; (*) echo $baz ;; esac)’ instead, which would work but not
serve as example for this portability issue.
x=$(case $foo in bar) echo $bar ;; *) echo $baz ;; esac)
# above fails to parse on old shells; below is the workaround
x=$(eval $(cat)) <<"EOF"
case $foo in bar) echo $bar ;; *) echo $baz ;; esac
EOF
Arithmetic substitutions are replaced by the value of the specified
expression. For example, the command print $((2+3*4)) displays 14. See
Arithmetic expressions for a description of an expression.
Parameters
Parameters are shell variables; they can be assigned values and their
values can be accessed using a parameter substitution. A parameter name
is either one of the special single punctuation or digit character param‐
eters described below, or a letter followed by zero or more letters or
digits (‘_’ counts as a letter). The latter form can be treated as
arrays by appending an array index of the form [expr] where expr is an
arithmetic expression. Array indices in mksh are limited to the range 0
through 4294967295, inclusive. That is, they are a 32-bit unsigned inte‐
ger.
Parameter substitutions take the form $name, ${name}, or ${name[expr]}
where name is a parameter name. Substitution of all array elements with
${name[*]} and ${name[@]} works equivalent to $* and $@ for positional
parameters. If substitution is performed on a parameter (or an array
parameter element) that is not set, a null string is substituted unless
the nounset option (set -o nounset or set -u) is set, in which case an
error occurs.
Parameters can be assigned values in a number of ways. First, the shell
implicitly sets some parameters like ‘#’, ‘PWD’, and ‘$’; this is the
only way the special single character parameters are set. Second, param‐
eters are imported from the shell's environment at startup. Third,
parameters can be assigned values on the command line: for example,
FOO=bar sets the parameter “FOO” to “bar”; multiple parameter assignments
can be given on a single command line and they can be followed by a sim‐
ple-command, in which case the assignments are in effect only for the
duration of the command (such assignments are also exported; see below
for the implications of this). Note that both the parameter name and the
‘=’ must be unquoted for the shell to recognise a parameter assignment.
The construct FOO+=baz is also recognised; the old and new values are
immediately concatenated. The fourth way of setting a parameter is with
the export, global, readonly, and typeset commands; see their descrip‐
tions in the Command execution section. Fifth, for and select loops set
parameters as well as the getopts, read, and set -A commands. Lastly,
parameters can be assigned values using assignment operators inside
arithmetic expressions (see Arithmetic expressions below) or using the
${name=value} form of the parameter substitution (see below).
Parameters with the export attribute (set using the export or typeset -x
commands, or by parameter assignments followed by simple commands) are
put in the environment (see environ(7)) of commands run by the shell as
name=value pairs. The order in which parameters appear in the environ‐
ment of a command is unspecified. When the shell starts up, it extracts
parameters and their values from its environment and automatically sets
the export attribute for those parameters.
Modifiers can be applied to the ${name} form of parameter substitution:
${name:-word}
If name is set and not NULL, it is substituted; otherwise, word
is substituted.
${name:+word}
If name is set and not NULL, word is substituted; otherwise,
nothing is substituted.
${name:=word}
If name is set and not NULL, it is substituted; otherwise, it is
assigned word and the resulting value of name is substituted.
${name:?word}
If name is set and not NULL, it is substituted; otherwise, word
is printed on standard error (preceded by name:) and an error
occurs (normally causing termination of a shell script, function,
or script sourced using the ‘.’ built-in). If word is omitted,
the string “parameter null or not set” is used instead. Cur‐
rently a bug, if word is a variable which expands to the null
string, the error message is also printed.
Note that, for all of the above, word is actually considered quoted, and
special parsing rules apply. The parsing rules also differ on whether
the expression is double-quoted: word then uses double-quoting rules,
except for the double quote itself (‘"’) and the closing brace, which, if
backslash escaped, gets quote removal applied.
In the above modifiers, the ‘:’ can be omitted, in which case the condi‐
tions only depend on name being set (as opposed to set and not NULL). If
word is needed, parameter, command, arithmetic, and tilde substitution
are performed on it; if word is not needed, it is not evaluated.
The following forms of parameter substitution can also be used (if name
is an array, the element with the key “0” will be substituted in scalar
context):
${#name}
The number of positional parameters if name is ‘*’, ‘@’, or not
specified; otherwise the length (in characters) of the string
value of parameter name.
${#name[*]}
${#name[@]}
The number of elements in the array name.
${%name}
The width (in screen columns) of the string value of parameter
name, or -1 if ${name} contains a control character.
${!name}
The name of the variable referred to by name. This will be name
except when name is a name reference (bound variable), created by
the nameref command (which is an alias for typeset -n).
${!name[*]}
${!name[@]}
The names of indices (keys) in the array name.
${name#pattern}
${name##pattern}
If pattern matches the beginning of the value of parameter name,
the matched text is deleted from the result of substitution. A
single ‘#’ results in the shortest match, and two of them result
in the longest match. Cannot be applied to a vector (${*} or
${@} or ${array[*]} or ${array[@]}).
${name%pattern}
${name%%pattern}
Like ${..#..} substitution, but it deletes from the end of the
value. Cannot be applied to a vector.
${name/pattern/string}
${name/#pattern/string}
${name/%pattern/string}
${name//pattern/string}
The longest match of pattern in the value of parameter name is
replaced with string (deleted if string is empty; the trailing
slash (‘/’) may be omitted in that case). A leading slash fol‐
lowed by ‘#’ or ‘%’ causes the pattern to be anchored at the
beginning or end of the value, respectively; empty unanchored
patterns cause no replacement; a single leading slash or use of a
pattern that matches the empty string causes the replacement to
happen only once; two leading slashes cause all occurrences of
matches in the value to be replaced. Cannot be applied to a vec‐
tor. Inefficiently implemented, may be slow.
${name:pos:len}
The first len characters of name, starting at position pos, are
substituted. Both pos and :len are optional. If pos is nega‐
tive, counting starts at the end of the string; if it is omitted,
it defaults to 0. If len is omitted or greater than the length
of the remaining string, all of it is substituted. Both pos and
len are evaluated as arithmetic expressions. Currently, pos must
start with a space, opening parenthesis or digit to be recog‐
nised. Cannot be applied to a vector.
${name@#}
The hash (using the BAFH algorithm) of the expansion of name.
This is also used internally for the shell's hashtables.
${name@Q}
A quoted expression safe for re-entry, whose value is the value
of the name parameter, is substituted.
Note that pattern may need extended globbing pattern (@(...)), single
('...') or double ("...") quote escaping unless -o sh is set.
The following special parameters are implicitly set by the shell and can‐
not be set directly using assignments:
! Process ID of the last background process started. If no back‐
ground processes have been started, the parameter is not set.
# The number of positional parameters ($1, $2, etc.).
$ The PID of the shell, or the PID of the original shell if it is a
subshell. Do NOT use this mechanism for generating temporary
file names; see mktemp(1) instead.
- The concatenation of the current single letter options (see the
set command below for a list of options).
? The exit status of the last non-asynchronous command executed.
If the last command was killed by a signal, $? is set to 128 plus
the signal number, but at most 255.
0 The name of the shell, determined as follows: the first argument
to mksh if it was invoked with the -c option and arguments were
given; otherwise the file argument, if it was supplied; or else
the basename the shell was invoked with (i.e. argv[0]). $0 is
also set to the name of the current script or the name of the
current function, if it was defined with the function keyword
(i.e. a Korn shell style function).
1 .. 9 The first nine positional parameters that were supplied to the
shell, function, or script sourced using the ‘.’ built-in. Fur‐
ther positional parameters may be accessed using ${number}.
* All positional parameters (except 0), i.e. $1, $2, $3, ...
If used outside of double quotes, parameters are separate words
(which are subjected to word splitting); if used within double
quotes, parameters are separated by the first character of the
IFS parameter (or the empty string if IFS is NULL).
@ Same as $*, unless it is used inside double quotes, in which case
a separate word is generated for each positional parameter. If
there are no positional parameters, no word is generated. $@ can
be used to access arguments, verbatim, without losing NULL argu‐
ments or splitting arguments with spaces.
The following parameters are set and/or used by the shell:
_ (underscore) When an external command is executed by the
shell, this parameter is set in the environment of the new
process to the path of the executed command. In interactive
use, this parameter is also set in the parent shell to the
last word of the previous command.
BASHPID The PID of the shell or subshell.
CDPATH Like PATH, but used to resolve the argument to the cd built-
in command. Note that if CDPATH is set and does not contain
‘.’ or an empty string element, the current directory is not
searched. Also, the cd built-in command will display the
resulting directory when a match is found in any search path
other than the empty path.
COLUMNS Set to the number of columns on the terminal or window.
Always set, defaults to 80, unless the value as reported by
stty(1) is non-zero and sane enough (minimum is 12x3); simi‐
lar for LINES. This parameter is used by the interactive
line editing modes, and by the select, set -o, and kill -l
commands to format information columns. Importing from the
environment or unsetting this parameter removes the binding
to the actual terminal size in favour of the provided value.
ENV If this parameter is found to be set after any profile files
are executed, the expanded value is used as a shell startup
file. It typically contains function and alias definitions.
ERRNO Integer value of the shell's errno variable. It indicates
the reason the last system call failed. Not yet imple‐
mented.
EXECSHELL If set, this parameter is assumed to contain the shell that
is to be used to execute commands that execve(2) fails to
execute and which do not start with a “#!shell” sequence.
FCEDIT The editor used by the fc command (see below).
FPATH Like PATH, but used when an undefined function is executed
to locate the file defining the function. It is also
searched when a command can't be found using PATH. See
Functions below for more information.
HISTFILE The name of the file used to store command history. When
assigned to or unset, the file is opened, history is trun‐
cated then loaded from the file; subsequent new commands
(possibly consisting of several lines) are appended once
they successfully compiled. Also, several invocations of
the shell will share history if their HISTFILE parameters
all point to the same file.
Note: If HISTFILE is unset or empty, no history file is
used. This is different from AT&T UNIX ksh.
HISTSIZE The number of commands normally stored for history. The
default is 2047. Do not set this value to insanely high
values such as 1000000000 because mksh can then not allocate
enough memory for the history and will not start.
HOME The default directory for the cd command and the value sub‐
stituted for an unqualified ~ (see Tilde expansion below).
IFS Internal field separator, used during substitution and by
the read command, to split values into distinct arguments;
normally set to space, tab, and newline. See Substitution
above for details.
Note: This parameter is not imported from the environment
when the shell is started.
KSHEGID The effective group id of the shell.
KSHGID The real group id of the shell.
KSHUID The real user id of the shell.
KSH_VERSION The name and version of the shell (read-only). See also the
version commands in Emacs editing mode and Vi editing mode
sections, below.
LINENO The line number of the function or shell script that is cur‐
rently being executed.
LINES Set to the number of lines on the terminal or window.
Always set, defaults to 24. See COLUMNS.
EPOCHREALTIME
Time since the epoch, as returned by gettimeofday(2), for‐
matted as decimal tv_sec followed by a dot (‘.’) and tv_usec
padded to exactly six decimal digits.
OLDPWD The previous working directory. Unset if cd has not suc‐
cessfully changed directories since the shell started, or if
the shell doesn't know where it is.
OPTARG When using getopts, it contains the argument for a parsed
option, if it requires one.
OPTIND The index of the next argument to be processed when using
getopts. Assigning 1 to this parameter causes getopts to
process arguments from the beginning the next time it is
invoked.
PATH A colon (semicolon on OS/2) separated list of directories
that are searched when looking for commands and files
sourced using the ‘.’ command (see below). An empty string
resulting from a leading or trailing colon, or two adjacent
colons, is treated as a ‘.’ (the current directory).
PGRP The process ID of the shell's process group leader.
PIPESTATUS An array containing the errorlevel (exit status) codes, one
by one, of the last pipeline run in the foreground.
PPID The process ID of the shell's parent.
PS1 The primary prompt for interactive shells. Parameter, com‐
mand, and arithmetic substitutions are performed, and ‘!’ is
replaced with the current command number (see the fc command
below). A literal ‘!’ can be put in the prompt by placing
‘!!’ in PS1.
The default prompt is ‘$ ’ for non-root users, ‘# ’ for
root. If mksh is invoked by root and PS1 does not contain a
‘#’ character, the default value will be used even if PS1
already exists in the environment.
The mksh distribution comes with a sample dot.mkshrc con‐
taining a sophisticated example, but you might like the fol‐
lowing one (note that ${HOSTNAME:=$(hostname)} and the root-
vs-user distinguishing clause are (in this example) executed
at PS1 assignment time, while the $USER and $PWD are escaped
and thus will be evaluated each time a prompt is displayed):
PS1='${USER:=$(id -un)}'"@${HOSTNAME:=$(hostname)}:\$PWD $(
if (( USER_ID )); then print \$; else print \#; fi) "
Note that since the command-line editors try to figure out
how long the prompt is (so they know how far it is to the
edge of the screen), escape codes in the prompt tend to mess
things up. You can tell the shell not to count certain
sequences (such as escape codes) by prefixing your prompt
with a character (such as Ctrl-A) followed by a carriage
return and then delimiting the escape codes with this char‐
acter. Any occurrences of that character in the prompt are
not printed. By the way, don't blame me for this hack; it's
derived from the original ksh88(1), which did print the
delimiter character so you were out of luck if you did not
have any non-printing characters.
Since Backslashes and other special characters may be inter‐
preted by the shell, to set PS1 either escape the backslash
itself, or use double quotes. The latter is more practical.
This is a more complex example, avoiding to directly enter
special characters (for example with ^V in the emacs editing
mode), which embeds the current working directory, in
reverse video (colour would work, too), in the prompt
string:
x=$(print \\001)
PS1="$x$(print \\r)$x$(tput so)$x\$PWD$x$(tput se)$x> "
Due to a strong suggestion from David G. Korn, mksh now also
supports the following form:
PS1=$'\1\r\1\e[7m\1$PWD\1\e[0m\1> '
PS2 Secondary prompt string, by default ‘> ’, used when more
input is needed to complete a command.
PS3 Prompt used by the select statement when reading a menu
selection. The default is ‘#? ’.
PS4 Used to prefix commands that are printed during execution
tracing (see the set -x command below). Parameter, command,
and arithmetic substitutions are performed before it is
printed. The default is ‘+ ’. You may want to set it to
‘[$EPOCHREALTIME] ’ instead, to include timestamps.
PWD The current working directory. May be unset or NULL if the
shell doesn't know where it is.
RANDOM Each time RANDOM is referenced, it is assigned a number
between 0 and 32767 from a Linear Congruential PRNG first.
REPLY Default parameter for the read command if no names are
given. Also used in select loops to store the value that is
read from standard input.
SECONDS The number of seconds since the shell started or, if the
parameter has been assigned an integer value, the number of
seconds since the assignment plus the value that was
assigned.
TMOUT If set to a positive integer in an interactive shell, it
specifies the maximum number of seconds the shell will wait
for input after printing the primary prompt (PS1). If the
time is exceeded, the shell exits.
TMPDIR The directory temporary shell files are created in. If this
parameter is not set, or does not contain the absolute path
of a writable directory, temporary files are created in
/tmp.
USER_ID The effective user id of the shell.
Tilde expansion
Tilde expansion which is done in parallel with parameter substitution, is
done on words starting with an unquoted ‘~’. The characters following
the tilde, up to the first ‘/’, if any, are assumed to be a login name.
If the login name is empty, ‘+’, or ‘-’, the value of the HOME, PWD, or
OLDPWD parameter is substituted, respectively. Otherwise, the password
file is searched for the login name, and the tilde expression is substi‐
tuted with the user's home directory. If the login name is not found in
the password file or if any quoting or parameter substitution occurs in
the login name, no substitution is performed.
In parameter assignments (such as those preceding a simple-command or
those occurring in the arguments of alias, export, global, readonly, and
typeset), tilde expansion is done after any assignment (i.e. after the
equals sign) or after an unquoted colon (‘:’); login names are also
delimited by colons.
The home directory of previously expanded login names are cached and re-
used. The alias -d command may be used to list, change, and add to this
cache (e.g. alias -d fac=/usr/local/facilities; cd ~fac/bin).
Brace expansion (alternation)
Brace expressions take the following form:
prefix{str1,...,strN}suffix
The expressions are expanded to N words, each of which is the concatena‐
tion of prefix, stri, and suffix (e.g. “a{c,b{X,Y},d}e” expands to four
words: “ace”, “abXe”, “abYe”, and “ade”). As noted in the example, brace
expressions can be nested and the resulting words are not sorted. Brace
expressions must contain an unquoted comma (‘,’) for expansion to occur
(e.g. {} and {foo} are not expanded). Brace expansion is carried out
after parameter substitution and before file name generation.
File name patterns
A file name pattern is a word containing one or more unquoted ‘?’, ‘*’,
‘+’, ‘@’, or ‘!’ characters or “[..]” sequences. Once brace expansion
has been performed, the shell replaces file name patterns with the sorted
names of all the files that match the pattern (if no files match, the
word is left unchanged). The pattern elements have the following mean‐
ing:
? Matches any single character.
* Matches any sequence of octets.
[..] Matches any of the octets inside the brackets. Ranges of octets
can be specified by separating two octets by a ‘-’ (e.g. “[a0-9]”
matches the letter ‘a’ or any digit). In order to represent
itself, a ‘-’ must either be quoted or the first or last octet in
the octet list. Similarly, a ‘]’ must be quoted or the first
octet in the list if it is to represent itself instead of the end
of the list. Also, a ‘!’ appearing at the start of the list has
special meaning (see below), so to represent itself it must be
quoted or appear later in the list.
[!..] Like [..], except it matches any octet not inside the brackets.
*(pattern|...|pattern)
Matches any string of octets that matches zero or more occur‐
rences of the specified patterns. Example: The pattern
*(foo|bar) matches the strings “”, “foo”, “bar”, “foobarfoo”,
etc.
+(pattern|...|pattern)
Matches any string of octets that matches one or more occurrences
of the specified patterns. Example: The pattern +(foo|bar)
matches the strings “foo”, “bar”, “foobar”, etc.
?(pattern|...|pattern)
Matches the empty string or a string that matches one of the
specified patterns. Example: The pattern ?(foo|bar) only matches
the strings “”, “foo”, and “bar”.
@(pattern|...|pattern)
Matches a string that matches one of the specified patterns.
Example: The pattern @(foo|bar) only matches the strings “foo”
and “bar”.
!(pattern|...|pattern)
Matches any string that does not match one of the specified pat‐
terns. Examples: The pattern !(foo|bar) matches all strings
except “foo” and “bar”; the pattern !(*) matches no strings; the
pattern !(?)* matches all strings (think about it).
Note that complicated globbing, especially with alternatives, is slow;
using separate comparisons may (or may not) be faster.
Note that mksh (and pdksh) never matches ‘.’ and ‘..’, but AT&T UNIX ksh,
Bourne sh, and GNU bash do.
Note that none of the above pattern elements match either a period (‘.’)
at the start of a file name or a slash (‘/’), even if they are explicitly
used in a [..] sequence; also, the names ‘.’ and ‘..’ are never matched,
even by the pattern ‘.*’.
If the markdirs option is set, any directories that result from file name
generation are marked with a trailing ‘/’.
Input/output redirection
When a command is executed, its standard input, standard output, and
standard error (file descriptors 0, 1, and 2, respectively) are normally
inherited from the shell. Three exceptions to this are commands in pipe‐
lines, for which standard input and/or standard output are those set up
by the pipeline, asynchronous commands created when job control is dis‐
abled, for which standard input is initially set to be from /dev/null,
and commands for which any of the following redirections have been speci‐
fied:
>file Standard output is redirected to file. If file does not
exist, it is created; if it does exist, is a regular file,
and the noclobber option is set, an error occurs; otherwise,
the file is truncated. Note that this means the command cmd
<foo >foo will open foo for reading and then truncate it when
it opens it for writing, before cmd gets a chance to actually
read foo.
>|file Same as >, except the file is truncated, even if the
noclobber option is set.
>>file Same as >, except if file exists it is appended to instead of
being truncated. Also, the file is opened in append mode, so
writes always go to the end of the file (see open(2)).
<file Standard input is redirected from file, which is opened for
reading.
<>file Same as <, except the file is opened for reading and writing.
<<marker After reading the command line containing this kind of redi‐
rection (called a “here document”), the shell copies lines
from the command source into a temporary file until a line
matching marker is read. When the command is executed, stan‐
dard input is redirected from the temporary file. If marker
contains no quoted characters, the contents of the temporary
file are processed as if enclosed in double quotes each time
the command is executed, so parameter, command, and arith‐
metic substitutions are performed, along with backslash (‘\’)
escapes for ‘$’, ‘`’, ‘\’, and ‘\newline’, but not for ‘"’.
If multiple here documents are used on the same command line,
they are saved in order.
If no marker is given, the here document ends at the next <<
and substitution will be performed. If marker is only a set
of either single “''” or double ‘""’ quotes with nothing in
between, the here document ends at the next empty line and
substitution will not be performed.
<<-marker Same as <<, except leading tabs are stripped from lines in
the here document.
<<<word Same as <<, except that word is the here document. This is
called a here string.
<&fd Standard input is duplicated from file descriptor fd. fd can
be a number, indicating the number of an existing file
descriptor; the letter ‘p’, indicating the file descriptor
associated with the output of the current co-process; or the
character ‘-’, indicating standard input is to be closed.
Note that fd is limited to a single digit in most shell
implementations.
>&fd Same as <&, except the operation is done on standard output.
&>file Same as >file 2>&1. This is a deprecated (legacy) GNU bash
extension supported by mksh which also supports the preceding
explicit fd number, for example, 3&>file is the same as
3>file 2>&3 in mksh but a syntax error in GNU bash.
&>|file, &>>file, &>&fd
Same as >|file, >>file, or >&fd, followed by 2>&1, as above.
These are mksh extensions.
In any of the above redirections, the file descriptor that is redirected
(i.e. standard input or standard output) can be explicitly given by pre‐
ceding the redirection with a number (portably, only a single digit).
Parameter, command, and arithmetic substitutions, tilde substitutions,
and (if the shell is interactive) file name generation are all performed
on the file, marker, and fd arguments of redirections. Note, however,
that the results of any file name generation are only used if a single
file is matched; if multiple files match, the word with the expanded file
name generation characters is used. Note that in restricted shells,
redirections which can create files cannot be used.
For simple-commands, redirections may appear anywhere in the command; for
compound-commands (if statements, etc.), any redirections must appear at
the end. Redirections are processed after pipelines are created and in
the order they are given, so the following will print an error with a
line number prepended to it:
$ cat /foo/bar 2>&1 >/dev/null | pr -n -t
File descriptors created by I/O redirections are private to the shell.
Arithmetic expressions
Integer arithmetic expressions can be used with the let command, inside
$((..)) expressions, inside array references (e.g. name[expr]), as
numeric arguments to the test command, and as the value of an assignment
to an integer parameter. Warning: This also affects implicit conversion
to integer, for example as done by the let command. Never use unchecked
user input, e.g. from the environment, in arithmetics!
Expressions are calculated using signed arithmetic and the mksh_ari_t
type (a 32-bit signed integer), unless they begin with a sole ‘#’ charac‐
ter, in which case they use mksh_uari_t (a 32-bit unsigned integer).
Expressions may contain alpha-numeric parameter identifiers, array refer‐
ences, and integer constants and may be combined with the following C
operators (listed and grouped in increasing order of precedence):
Unary operators:
+ - ! ~ ++ --
Binary operators:
,
= += -= *= /= %= <<<= >>>= <<= >>= &= ^= |=
||
&&
|
^
&
== !=
< <= > >=
<<< >>> << >>
+ -
* / %
Ternary operators:
?: (precedence is immediately higher than assignment)
Grouping operators:
( )
Integer constants and expressions are calculated using an exactly 32-bit
wide, signed or unsigned, type with silent wraparound on integer over‐
flow. Integer constants may be specified with arbitrary bases using the
notation base#number, where base is a decimal integer specifying the
base, and number is a number in the specified base. Additionally,
base-16 integers may be specified by prefixing them with ‘0x’
(case-insensitive) in all forms of arithmetic expressions, except as
numeric arguments to the test built-in command. Prefixing numbers with a
sole digit zero (‘0’) does not cause interpretation as octal, as that's
unsafe to do.
As a special mksh extension, numbers to the base of one are treated as
either (8-bit transparent) ASCII or Unicode codepoints, depending on the
shell's utf8-mode flag (current setting). The AT&T UNIX ksh93 syntax of
“'x'” instead of “1#x” is also supported. Note that NUL bytes (integral
value of zero) cannot be used. An unset or empty parameter evaluates to
0 in integer context. In Unicode mode, raw octets are mapped into the
range EF80..EFFF as in OPTU-8, which is in the PUA and has been assigned
by CSUR for this use. If more than one octet in ASCII mode, or a
sequence of more than one octet not forming a valid and minimal CESU-8
sequence is passed, the behaviour is undefined (usually, the shell aborts
with a parse error, but rarely, it succeeds, e.g. on the sequence C2 20).
That's why you should always use ASCII mode unless you know that the
input is well-formed UTF-8 in the range of 0000..FFFD if you use this
feature, as opposed to read -a.
The operators are evaluated as follows:
unary +
Result is the argument (included for completeness).
unary -
Negation.
! Logical NOT; the result is 1 if argument is zero, 0 if not.
~ Arithmetic (bit-wise) NOT.
++ Increment; must be applied to a parameter (not a literal or
other expression). The parameter is incremented by 1.
When used as a prefix operator, the result is the incre‐
mented value of the parameter; when used as a postfix oper‐
ator, the result is the original value of the parameter.
-- Similar to ++, except the parameter is decremented by 1.
, Separates two arithmetic expressions; the left-hand side is
evaluated first, then the right. The result is the value
of the expression on the right-hand side.
= Assignment; the variable on the left is set to the value on
the right.
+= -= *= /= %= <<<= >>>= <<= >>= &= ^= |=
Assignment operators. <var><op>=<expr> is the same as
<var>=<var><op><expr>, with any operator precedence in
<expr> preserved. For example, “var1 *= 5 + 3” is the same
as specifying “var1 = var1 * (5 + 3)”.
|| Logical OR; the result is 1 if either argument is non-zero,
0 if not. The right argument is evaluated only if the left
argument is zero.
&& Logical AND; the result is 1 if both arguments are non-
zero, 0 if not. The right argument is evaluated only if
the left argument is non-zero.
| Arithmetic (bit-wise) OR.
^ Arithmetic (bit-wise) XOR (exclusive-OR).
& Arithmetic (bit-wise) AND.
== Equal; the result is 1 if both arguments are equal, 0 if
not.
!= Not equal; the result is 0 if both arguments are equal, 1
if not.
< Less than; the result is 1 if the left argument is less
than the right, 0 if not.
<= > >=
Less than or equal, greater than, greater than or equal.
See <.
<<< >>>
Rotate left (right); the result is similar to shift (see
<<) except that the bits shifted out at one end are shifted
in at the other end, instead of zero or sign bits.
<< >> Shift left (right); the result is the left argument with
its bits shifted left (right) by the amount given in the
right argument.
+ - * /
Addition, subtraction, multiplication, and division.
% Remainder; the result is the symmetric remainder of the
division of the left argument by the right. To get the
mathematical modulus of “a mod b”, use the formula “(a % b
+ b) % b”.
<arg1>?<arg2>:<arg3>
If <arg1> is non-zero, the result is <arg2>; otherwise the
result is <arg3>. The non-result argument is not evalu‐
ated.
Co-processes
A co-process (which is a pipeline created with the ‘|&’ operator) is an
asynchronous process that the shell can both write to (using print -p)
and read from (using read -p). The input and output of the co-process
can also be manipulated using >&p and <&p redirections, respectively.
Once a co-process has been started, another can't be started until the
co-process exits, or until the co-process's input has been redirected
using an exec n>&p redirection. If a co-process's input is redirected in
this way, the next co-process to be started will share the output with
the first co-process, unless the output of the initial co-process has
been redirected using an exec n<&p redirection.
Some notes concerning co-processes:
· The only way to close the co-process's input (so the co-process reads
an end-of-file) is to redirect the input to a numbered file descrip‐
tor and then close that file descriptor: exec 3>&p; exec 3>&-
· In order for co-processes to share a common output, the shell must
keep the write portion of the output pipe open. This means that end-
of-file will not be detected until all co-processes sharing the co-
process's output have exited (when they all exit, the shell closes
its copy of the pipe). This can be avoided by redirecting the output
to a numbered file descriptor (as this also causes the shell to close
its copy). Note that this behaviour is slightly different from the
original Korn shell which closes its copy of the write portion of the
co-process output when the most recently started co-process (instead
of when all sharing co-processes) exits.
· print -p will ignore SIGPIPE signals during writes if the signal is
not being trapped or ignored; the same is true if the co-process
input has been duplicated to another file descriptor and print -un is
used.
Functions
Functions are defined using either Korn shell function function-name syn‐
tax or the Bourne/POSIX shell function-name() syntax (see below for the
difference between the two forms). Functions are like .‐scripts (i.e.
scripts sourced using the ‘.’ built-in) in that they are executed in the
current environment. However, unlike .‐scripts, shell arguments (i.e.
positional parameters $1, $2, etc.) are never visible inside them. When
the shell is determining the location of a command, functions are
searched after special built-in commands, before builtins and the PATH is
searched.
An existing function may be deleted using unset -f function-name. A list
of functions can be obtained using typeset +f and the function defini‐
tions can be listed using typeset -f. The autoload command (which is an
alias for typeset -fu) may be used to create undefined functions: when an
undefined function is executed, the shell searches the path specified in
the FPATH parameter for a file with the same name as the function which,
if found, is read and executed. If after executing the file the named
function is found to be defined, the function is executed; otherwise, the
normal command search is continued (i.e. the shell searches the regular
built-in command table and PATH). Note that if a command is not found
using PATH, an attempt is made to autoload a function using FPATH (this
is an undocumented feature of the original Korn shell).
Functions can have two attributes, “trace” and “export”, which can be set
with typeset -ft and typeset -fx, respectively. When a traced function
is executed, the shell's xtrace option is turned on for the function's
duration. The “export” attribute of functions is currently not used. In
the original Korn shell, exported functions are visible to shell scripts
that are executed.
Since functions are executed in the current shell environment, parameter
assignments made inside functions are visible after the function com‐
pletes. If this is not the desired effect, the typeset command can be
used inside a function to create a local parameter. Note that AT&T UNIX
ksh93 uses static scoping (one global scope, one local scope per func‐
tion) and allows local variables only on Korn style functions, whereas
mksh uses dynamic scoping (nested scopes of varying locality). Note that
special parameters (e.g. $$, $!) can't be scoped in this way.
The exit status of a function is that of the last command executed in the
function. A function can be made to finish immediately using the return
command; this may also be used to explicitly specify the exit status.
Functions defined with the function reserved word are treated differently
in the following ways from functions defined with the () notation:
· The $0 parameter is set to the name of the function (Bourne-style
functions leave $0 untouched).
· Parameter assignments preceding function calls are not kept in the
shell environment (executing Bourne-style functions will keep assign‐
ments).
· OPTIND is saved/reset and restored on entry and exit from the func‐
tion so getopts can be used properly both inside and outside the
function (Bourne-style functions leave OPTIND untouched, so using
getopts inside a function interferes with using getopts outside the
function).
· Shell options (set -o) have local scope, i.e. changes inside a func‐
tion are reset upon its exit.
In the future, the following differences may also be added:
· A separate trap/signal environment will be used during the execution
of functions. This will mean that traps set inside a function will
not affect the shell's traps and signals that are not ignored in the
shell (but may be trapped) will have their default effect in a func‐
tion.
· The EXIT trap, if set in a function, will be executed after the func‐
tion returns.
Command execution
After evaluation of command-line arguments, redirections, and parameter
assignments, the type of command is determined: a special built-in com‐
mand, a function, a normal builtin, or the name of a file to execute
found using the PATH parameter. The checks are made in the above order.
Special built-in commands differ from other commands in that the PATH
parameter is not used to find them, an error during their execution can
cause a non-interactive shell to exit, and parameter assignments that are
specified before the command are kept after the command completes. Regu‐
lar built-in commands are different only in that the PATH parameter is
not used to find them.
The original ksh and POSIX differ somewhat in which commands are consid‐
ered special or regular.
POSIX special built-in utilities:
., :, break, continue, eval, exec, exit, export, readonly, return, set,
shift, times, trap, unset
Additional mksh commands keeping assignments:
builtin, global, source, typeset, wait
Builtins that are not special:
[, alias, bg, bind, cat, cd, command, echo, false, fc, fg, getopts, jobs,
kill, let, print, pwd, read, realpath, rename, sleep, suspend, test,
true, ulimit, umask, unalias, whence
Once the type of command has been determined, any command-line parameter
assignments are performed and exported for the duration of the command.
The following describes the special and regular built-in commands and
builtin-like reserved words:
. file [arg ...]
This is called the “dot” command. Execute the commands in file in
the current environment. The file is searched for in the directo‐
ries of PATH. If arguments are given, the positional parameters
may be used to access them while file is being executed. If no
arguments are given, the positional parameters are those of the
environment the command is used in.
: [...]
The null command. Exit status is set to zero.
[ expression ]
See test.
alias [-d | -t [-r] | +-x] [-p] [+] [name [=value] ...]
Without arguments, alias lists all aliases. For any name without
a value, the existing alias is listed. Any name with a value
defines an alias (see Aliases above).
When listing aliases, one of two formats is used. Normally,
aliases are listed as name=value, where value is quoted. If
options were preceded with ‘+’, or a lone ‘+’ is given on the com‐
mand line, only name is printed.
The -d option causes directory aliases which are used in tilde
expansion to be listed or set (see Tilde expansion above).
If the -p option is used, each alias is prefixed with the string
“alias ”.
The -t option indicates that tracked aliases are to be listed/set
(values specified on the command line are ignored for tracked
aliases). The -r option indicates that all tracked aliases are to
be reset.
The -x option sets (+x clears) the export attribute of an alias,
or, if no names are given, lists the aliases with the export
attribute (exporting an alias has no effect).
bg [job ...]
Resume the specified stopped job(s) in the background. If no jobs
are specified, %+ is assumed. See Job control below for more
information.
bind [-l]
The current bindings are listed. If the -l flag is given, bind
instead lists the names of the functions to which keys may be
bound. See Emacs editing mode for more information.
bind [-m] string=[substitute] ...
bind string=[editing-command] ...
The specified editing command is bound to the given string, which
should consist of a control character optionally preceded by one
of the two prefix characters and optionally succeded by a tilde
character. Future input of the string will cause the editing com‐
mand to be immediately invoked. If the -m flag is given, the
specified input string will afterwards be immediately replaced by
the given substitute string which may contain editing commands but
not other macros. If a tilde postfix is given, a tilde trailing
the one or two prefices and the control character is ignored, any
other trailing character will be processed afterwards.
Control characters may be written using caret notation i.e. ^X
represents Ctrl-X. Note that although only two prefix characters
(usually ESC and ^X) are supported, some multi-character sequences
can be supported.
The following default bindings show how the arrow keys, the home,
end and delete key on a BSD wsvt25, xterm-xfree86 or GNU screen
terminal are bound (of course some escape sequences won't work out
quite this nicely):
bind '^X'=prefix-2
bind '^[['=prefix-2
bind '^XA'=up-history
bind '^XB'=down-history
bind '^XC'=forward-char
bind '^XD'=backward-char
bind '^X1~'=beginning-of-line
bind '^X7~'=beginning-of-line
bind '^XH'=beginning-of-line
bind '^X4~'=end-of-line
bind '^X8~'=end-of-line
bind '^XF'=end-of-line
bind '^X3~'=delete-char-forward
break [level]
Exit the levelth inner-most for, select, until, or while loop.
level defaults to 1.
builtin [--] command [arg ...]
Execute the built-in command command.
cat [-u] [file ...]
Read files sequentially, in command line order, and write them to
standard output. If a file is a single dash (‘-’) or absent, read
from standard input. For direct builtin calls, the POSIX -u
option is supported as a no-op. For calls from shell, if any
options are given, an external cat(1) utility is preferred over
the builtin.
cd [-L] [dir]
cd -P [-e] [dir]
chdir [-eLP] [dir]
Set the working directory to dir. If the parameter CDPATH is set,
it lists the search path for the directory containing dir. A NULL
path means the current directory. If dir is found in any compo‐
nent of the CDPATH search path other than the NULL path, the name
of the new working directory will be written to standard output.
If dir is missing, the home directory HOME is used. If dir is
‘-’, the previous working directory is used (see the OLDPWD param‐
eter).
If the -L option (logical path) is used or if the physical option
isn't set (see the set command below), references to ‘..’ in dir
are relative to the path used to get to the directory. If the -P
option (physical path) is used or if the physical option is set,
‘..’ is relative to the filesystem directory tree. The PWD and
OLDPWD parameters are updated to reflect the current and old work‐
ing directory, respectively. If the -e option is set for physical
filesystem traversal, and PWD could not be set, the exit code is
1; greater than 1 if an error occurred, 0 otherwise.
cd [-eLP] old new
chdir [-eLP] old new
The string new is substituted for old in the current directory,
and the shell attempts to change to the new directory.
command [-pVv] cmd [arg ...]
If neither the -v nor -V option is given, cmd is executed exactly
as if command had not been specified, with two exceptions:
firstly, cmd cannot be a shell function; and secondly, special
built-in commands lose their specialness (i.e. redirection and
utility errors do not cause the shell to exit, and command assign‐
ments are not permanent).
If the -p option is given, a default search path is used instead
of the current value of PATH, the actual value of which is system
dependent.
If the -v option is given, instead of executing cmd, information
about what would be executed is given (and the same is done for
arg ...). For builtins, functions and keywords, their names are
simply printed; for aliases, a command that defines them is
printed; for utilities found by searching the PATH parameter, the
full path of the command is printed. If no command is found (i.e.
the path search fails), nothing is printed and command exits with
a non-zero status. The -V option is like the -v option, except it
is more verbose.
continue [level]
Jumps to the beginning of the levelth inner-most for, select,
until, or while loop. level defaults to 1.
echo [-Een] [arg ...]
Warning: this utility is not portable; use the Korn shell builtin
print instead.
Prints its arguments (separated by spaces) followed by a newline,
to the standard output. The newline is suppressed if any of the
arguments contain the backslash sequence ‘\c’. See the print com‐
mand below for a list of other backslash sequences that are recog‐
nised.
The options are provided for compatibility with BSD shell scripts.
The -n option suppresses the trailing newline, -e enables back‐
slash interpretation (a no-op, since this is normally done), and
-E suppresses backslash interpretation.
If the posix or sh option is set or this is a direct builtin call,
only the first argument is treated as an option, and only if it is
exactly “-n”. Backslash interpretation is disabled.
eval command ...
The arguments are concatenated (with spaces between them) to form
a single string which the shell then parses and executes in the
current environment.
exec [-a argv0] [-c] [command [arg ...]]
The command is executed without forking, replacing the shell
process. This is currently absolute, i.e. exec never returns,
even if the command is not found. The -a option permits setting a
different argv[0] value, and -c clears the environment before exe‐
cuting the child process, except for the _ variable and direct
assignments.
If no command is given except for I/O redirection, the I/O redi‐
rection is permanent and the shell is not replaced. Any file
descriptors greater than 2 which are opened or dup(2)'d in this
way are not made available to other executed commands (i.e. com‐
mands that are not built-in to the shell). Note that the Bourne
shell differs here; it does pass these file descriptors on.
exit [status]
The shell exits with the specified exit status. If status is not
specified, the exit status is the current value of the $? parame‐
ter.
export [-p] [parameter[=value]]
Sets the export attribute of the named parameters. Exported
parameters are passed in the environment to executed commands. If
values are specified, the named parameters are also assigned.
If no parameters are specified, all parameters with the export
attribute set are printed one per line; either their names, or, if
a ‘-’ with no option letter is specified, name=value pairs, or,
with -p, export commands suitable for re-entry.
false A command that exits with a non-zero status.
fc [-e editor | -l [-n]] [-r] [first [last]]
first and last select commands from the history. Commands can be
selected by history number (negative numbers go backwards from the
current, most recent, line) or a string specifying the most recent
command starting with that string. The -l option lists the com‐
mand on standard output, and -n inhibits the default command num‐
bers. The -r option reverses the order of the list. Without -l,
the selected commands are edited by the editor specified with the
-e option, or if no -e is specified, the editor specified by the
FCEDIT parameter (if this parameter is not set, /bin/ed is used),
and then executed by the shell.
fc -e - | -s [-g] [old=new] [prefix]
Re-execute the selected command (the previous command by default)
after performing the optional substitution of old with new. If -g
is specified, all occurrences of old are replaced with new. The
meaning of -e - and -s is identical: re-execute the selected com‐
mand without invoking an editor. This command is usually accessed
with the predefined: alias r='fc -e -'
fg [job ...]
Resume the specified job(s) in the foreground. If no jobs are
specified, %+ is assumed. See Job control below for more informa‐
tion.
getopts optstring name [arg ...]
Used by shell procedures to parse the specified arguments (or
positional parameters, if no arguments are given) and to check for
legal options. optstring contains the option letters that getopts
is to recognise. If a letter is followed by a colon, the option
is expected to have an argument. Options that do not take argu‐
ments may be grouped in a single argument. If an option takes an
argument and the option character is not the last character of the
argument it is found in, the remainder of the argument is taken to
be the option's argument; otherwise, the next argument is the
option's argument.
Each time getopts is invoked, it places the next option in the
shell parameter name and the index of the argument to be processed
by the next call to getopts in the shell parameter OPTIND. If the
option was introduced with a ‘+’, the option placed in name is
prefixed with a ‘+’. When an option requires an argument, getopts
places it in the shell parameter OPTARG.
When an illegal option or a missing option argument is encoun‐
tered, a question mark or a colon is placed in name (indicating an
illegal option or missing argument, respectively) and OPTARG is
set to the option character that caused the problem. Furthermore,
if optstring does not begin with a colon, a question mark is
placed in name, OPTARG is unset, and an error message is printed
to standard error.
When the end of the options is encountered, getopts exits with a
non-zero exit status. Options end at the first (non-option argu‐
ment) argument that does not start with a ‘-’, or when a ‘--’
argument is encountered.
Option parsing can be reset by setting OPTIND to 1 (this is done
automatically whenever the shell or a shell procedure is invoked).
Warning: Changing the value of the shell parameter OPTIND to a
value other than 1, or parsing different sets of arguments without
resetting OPTIND, may lead to unexpected results.
global ...
See typeset.
hash [-r] [name ...]
Without arguments, any hashed executable command pathnames are
listed. The -r option causes all hashed commands to be removed
from the hash table. Each name is searched as if it were a com‐
mand name and added to the hash table if it is an executable com‐
mand.
jobs [-lnp] [job ...]
Display information about the specified job(s); if no jobs are
specified, all jobs are displayed. The -n option causes informa‐
tion to be displayed only for jobs that have changed state since
the last notification. If the -l option is used, the process ID
of each process in a job is also listed. The -p option causes
only the process group of each job to be printed. See Job control
below for the format of job and the displayed job.
kill [-s signame | -signum | -signame] { job | pid | pgrp } ...
Send the specified signal to the specified jobs, process IDs, or
process groups. If no signal is specified, the TERM signal is
sent. If a job is specified, the signal is sent to the job's
process group. See Job control below for the format of job.
kill -l [exit-status ...]
Print the signal name corresponding to exit-status. If no argu‐
ments are specified, a list of all the signals, their numbers, and
a short description of them are printed.
let [expression ...]
Each expression is evaluated (see Arithmetic expressions above).
If all expressions are successfully evaluated, the exit status is
0 (1) if the last expression evaluated to non-zero (zero). If an
error occurs during the parsing or evaluation of an expression,
the exit status is greater than 1. Since expressions may need to
be quoted, (( expr )) is syntactic sugar for { let 'expr'; }.
let] Internally used alias for let.
mknod [-m mode] name b|c major minor
mknod [-m mode] name p
Create a device special file. The file type may be b (block type
device), c (character type device), or p (named pipe, FIFO). The
file created may be modified according to its mode (via the -m
option), major (major device number), and minor (minor device num‐
ber). This is not normally part of mksh; however, distributors
may have added this as builtin as a speed hack.
print [-nprsu[n] | -R [-en]] [argument ...]
print prints its arguments on the standard output, separated by
spaces and terminated with a newline. The -n option suppresses
the newline. By default, certain C escapes are translated. These
include these mentioned in Backslash expansion above, as well as
‘\c’, which is equivalent to using the -n option. Backslash
expansion may be inhibited with the -r option. The -s option
prints to the history file instead of standard output; the -u
option prints to file descriptor n (n defaults to 1 if omitted);
and the -p option prints to the co-process (see Co-processes
above).
The -R option is used to emulate, to some degree, the BSD echo(1)
command which does not process ‘\’ sequences unless the -e option
is given. As above, the -n option suppresses the trailing new‐
line.
printf format [arguments ...]
Formatted output. Approximately the same as the printf(1), util‐
ity, except it uses the same Backslash expansion and I/O code and
does not handle floating point as the rest of mksh. An external
utility is preferred over the builtin. This is not normally part
of mksh; however, distributors may have added this as builtin as a
speed hack. Do not use in new code.
pwd [-LP]
Print the present working directory. If the -L option is used or
if the physical option isn't set (see the set command below), the
logical path is printed (i.e. the path used to cd to the current
directory). If the -P option (physical path) is used or if the
physical option is set, the path determined from the filesystem
(by following ‘..’ directories to the root directory) is printed.
read [-A | -a] [-d x] [-N z | -n z] [-p | -u[n]] [-t n] [-rs] [p ...]
Reads a line of input, separates the input into fields using the
IFS parameter (see Substitution above), and assigns each field to
the specified parameters p. If no parameters are specified, the
REPLY parameter is used to store the result. With the -A and -a
options, only no or one parameter is accepted. If there are more
parameters than fields, the extra parameters are set to the empty
string or 0; if there are more fields than parameters, the last
parameter is assigned the remaining fields (including the word
separators).
The options are as follows:
-A Store the result into the parameter p (or REPLY) as array
of words.
-a Store the result without word splitting into the parameter
p (or REPLY) as array of characters (wide characters if the
utf8-mode option is enacted, octets otherwise); the code‐
points are encoded as decimal numbers by default.
-d x Use the first byte of x, NUL if empty, instead of the ASCII
newline character as input line delimiter.
-N z Instead of reading till end-of-line, read exactly z bytes.
If EOF or a timeout occurs, a partial read is returned with
exit status 1.
-n z Instead of reading till end-of-line, read up to z bytes but
return as soon as any bytes are read, e.g. from a slow ter‐
minal device, or if EOF or a timeout occurs.
-p Read from the currently active co-process, see Co-processes
above for details on this.
-u[n] Read from the file descriptor n (defaults to 0, i.e. stan‐
dard input). The argument must immediately follow the
option character.
-t n Interrupt reading after n seconds (specified as positive
decimal value with an optional fractional part). The exit
status of read is 1 if the timeout occurred, but partial
reads may still be returned.
-r Normally, the ASCII backslash character escapes the special
meaning of the following character and is stripped from the
input; read does not stop when encountering a backslash-
newline sequence and does not store that newline in the
result. This option enables raw mode, in which backslashes
are not processed.
-s The input line is saved to the history.
If the input is a terminal, both the -N and -n options set it into
raw mode; they read an entire file if -1 is passed as z argument.
The first parameter may have a question mark and a string appended
to it, in which case the string is used as a prompt (printed to
standard error before any input is read) if the input is a tty(4)
(e.g. read nfoo?'number of foos: ').
If no input is read or a timeout occurred, read exits with a non-
zero status.
Another handy set of tricks: If read is run in a loop such as
while read foo; do ...; done then leading whitespace will be
removed (IFS) and backslashes processed. You might want to use
while IFS= read -r foo; do ...; done for pristine I/O. Similar‐
ily, when using the -a option, use of the -r option might be pru‐
dent; the same applies for:
find . -type f -print0 |& \
while IFS= read -d '' -pr filename; do
print -r -- "found <${filename#./}>"
done
The inner loop will be executed in a subshell and variable changes
cannot be propagated if executed in a pipeline:
bar | baz | while read foo; do ...; done
Use co-processes instead:
bar | baz |&
while read -p foo; do ...; done
exec 3>&p; exec 3>&-
readonly [-p] [parameter [=value] ...]
Sets the read-only attribute of the named parameters. If values
are given, parameters are set to them before setting the
attribute. Once a parameter is made read-only, it cannot be unset
and its value cannot be changed.
If no parameters are specified, the names of all parameters with
the read-only attribute are printed one per line, unless the -p
option is used, in which case readonly commands defining all read-
only parameters, including their values, are printed.
realpath [--] name
Prints the resolved absolute pathname corresponding to name. If
name ends with a slash (‘/’), it's also checked for existence and
whether it is a directory; otherwise, realpath returns 0 if the
pathname either exists or can be created immediately, i.e. all but
the last component exist and are directories.
rename [--] from to
Renames the file from to to. Both must be complete pathnames and
on the same device. This builtin is intended for emergency situa‐
tions where /bin/mv becomes unusable, and directly calls
rename(2).
return [status]
Returns from a function or . script, with exit status status. If
no status is given, the exit status of the last executed command
is used. If used outside of a function or . script, it has the
same effect as exit. Note that mksh treats both profile and ENV
files as . scripts, while the original Korn shell only treats pro‐
files as . scripts.
set [+-abCefhiklmnprsUuvXx] [+-o option] [+-A name] [--] [arg ...]
The set command can be used to set (-) or clear (+) shell options,
set the positional parameters, or set an array parameter. Options
can be changed using the +-o option syntax, where option is the
long name of an option, or using the +-letter syntax, where letter
is the option's single letter name (not all options have a single
letter name). The following table lists both option letters (if
they exist) and long names along with a description of what the
option does:
-A name
Sets the elements of the array parameter name to arg ... If
-A is used, the array is reset (i.e. emptied) first; if +A is
used, the first N elements are set (where N is the number of
arguments); the rest are left untouched.
An alternative syntax for the command set -A foo -- a b c
which is compatible to GNU bash and also supported by AT&T
UNIX ksh93 is: foo=(a b c); foo+=(d e)
-a | -o allexport
All new parameters are created with the export attribute.
-b | -o notify
Print job notification messages asynchronously, instead of
just before the prompt. Only used if job control is enabled
(-m).
-C | -o noclobber
Prevent > redirection from overwriting existing files.
Instead, >| must be used to force an overwrite. Note that
this is not safe to use for creation of temporary files or
lockfiles due to a TOCTOU in a check allowing one to redirect
output to /dev/null or other device files even in noclobber
mode.
-e | -o errexit
Exit (after executing the ERR trap) as soon as an error
occurs or a command fails (i.e. exits with a non-zero sta‐
tus). This does not apply to commands whose exit status is
explicitly tested by a shell construct such as if, until,
while, or ! statements. For && or ||, only the status of the
last command is tested.
-f | -o noglob
Do not expand file name patterns.
-h | -o trackall
Create tracked aliases for all executed commands (see Aliases
above). Enabled by default for non-interactive shells.
-i | -o interactive
The shell is an interactive shell. This option can only be
used when the shell is invoked. See above for a description
of what this means.
-k | -o keyword
Parameter assignments are recognised anywhere in a command.
-l | -o login
The shell is a login shell. This option can only be used
when the shell is invoked. See above for a description of
what this means.
-m | -o monitor
Enable job control (default for interactive shells).
-n | -o noexec
Do not execute any commands. Useful for checking the syntax
of scripts (ignored if interactive).
-p | -o privileged
The shell is a privileged shell. It is set automatically if,
when the shell starts, the real UID or GID does not match the
effective UID (EUID) or GID (EGID), respectively. See above
for a description of what this means.
-r | -o restricted
The shell is a restricted shell. This option can only be
used when the shell is invoked. See above for a description
of what this means.
-s | -o stdin
If used when the shell is invoked, commands are read from
standard input. Set automatically if the shell is invoked
with no arguments.
When -s is used with the set command it causes the specified
arguments to be sorted before assigning them to the posi‐
tional parameters (or to array name, if -A is used).
-U | -o utf8-mode
Enable UTF-8 support in the Emacs editing mode and internal
string handling functions. This flag is disabled by default,
but can be enabled by setting it on the shell command line;
is enabled automatically for interactive shells if requested
at compile time, your system supports setlocale(LC_CTYPE, "")
and optionally nl_langinfo(CODESET), or the LC_ALL, LC_CTYPE,
or LANG environment variables, and at least one of these
returns something that matches “UTF-8” or “utf8” case-insen‐
sitively; for direct builtin calls depending on the aforemen‐
tioned environment variables; or for stdin or scripts, if the
input begins with a UTF-8 Byte Order Mark.
In near future, locale tracking will be implemented, which
means that set -+U is changed whenever one of the POSIX
locale-related environment variables changes.
-u | -o nounset
Referencing of an unset parameter, other than “$@” or “$*”,
is treated as an error, unless one of the ‘-’, ‘+’, or ‘=’
modifiers is used.
-v | -o verbose
Write shell input to standard error as it is read.
-X | -o markdirs
Mark directories with a trailing ‘/’ during file name genera‐
tion.
-x | -o xtrace
Print command trees when they are executed, preceded by the
value of PS4.
-o bgnice
Background jobs are run with lower priority.
-o braceexpand
Enable brace expansion (a.k.a. alternation). This is enabled
by default. If disabled, tilde expansion after an equals
sign is disabled as a side effect.
-o emacs
Enable BRL emacs-like command-line editing (interactive
shells only); see Emacs editing mode.
-o gmacs
Enable gmacs-like command-line editing (interactive shells
only). Currently identical to emacs editing except that
transpose-chars (^T) acts slightly differently.
-o ignoreeof
The shell will not (easily) exit when end-of-file is read;
exit must be used. To avoid infinite loops, the shell will
exit if EOF is read 13 times in a row.
-o inherit-xtrace
Do not reset -o xtrace upon entering functions. This is
enabled by default.
-o nohup
Do not kill running jobs with a SIGHUP signal when a login
shell exits. Currently set by default, but this may change
in the future to be compatible with AT&T UNIX ksh, which
doesn't have this option, but does send the SIGHUP signal.
-o nolog
No effect. In the original Korn shell, this prevents func‐
tion definitions from being stored in the history file.
-o physical
Causes the cd and pwd commands to use “physical” (i.e. the
filesystem's) ‘..’ directories instead of “logical” directo‐
ries (i.e. the shell handles ‘..’, which allows the user to
be oblivious of symbolic links to directories). Clear by
default. Note that setting this option does not affect the
current value of the PWD parameter; only the cd command
changes PWD. See the cd and pwd commands above for more
details.
-o pipefail
Make the exit status of a pipeline (before logically comple‐
menting) the rightmost non-zero errorlevel, or zero if all
commands exited with zero.
-o posix
Behave closer to the standards (see POSIX mode for details).
Automatically enabled if the basename of the shell invocation
begins with “sh” and this autodetection feature is compiled
in (not in MirBSD). As a side effect, setting this flag
turns off braceexpand mode, which can be turned back on manu‐
ally, and sh mode (unless both are enabled at the same time).
-o sh
Enable /bin/sh (kludge) mode (see SH mode). Automatically
enabled if the basename of the shell invocation begins with
“sh” and this autodetection feature is compiled in (not in
MirBSD). As a side effect, setting this flag turns off
braceexpand mode, which can be turned back on manually, and
posix mode (unless both are enabled at the same time).
-o vi
Enable vi(1)-like command-line editing (interactive shells
only). See Vi editing mode for documentation and limita‐
tions.
-o vi-esccomplete
In vi command-line editing, do command and file name comple‐
tion when escape (^[) is entered in command mode.
-o vi-tabcomplete
In vi command-line editing, do command and file name comple‐
tion when tab (^I) is entered in insert mode. This is the
default.
-o viraw
No effect. In the original Korn shell, unless viraw was set,
the vi command-line mode would let the tty(4) driver do the
work until ESC (^[) was entered. mksh is always in viraw
mode.
These options can also be used upon invocation of the shell. The
current set of options (with single letter names) can be found in
the parameter ‘$-’. set -o with no option name will list all the
options and whether each is on or off; set +o will print the long
names of all options that are currently on.
Remaining arguments, if any, are positional parameters and are
assigned, in order, to the positional parameters (i.e. $1, $2,
etc.). If options end with ‘--’ and there are no remaining argu‐
ments, all positional parameters are cleared. If no options or
arguments are given, the values of all names are printed. For
unknown historical reasons, a lone ‘-’ option is treated specially
– it clears both the -v and -x options.
shift [number]
The positional parameters number+1, number+2, etc. are renamed to
‘1’, ‘2’, etc. number defaults to 1.
sleep seconds
Suspends execution for a minimum of the seconds specified as posi‐
tive decimal value with an optional fractional part. Signal
delivery may continue execution earlier.
source file [arg ...]
Like . (“dot”), except that the current working directory is
appended to the search path (GNU bash extension).
suspend
Stops the shell as if it had received the suspend character from
the terminal. It is not possible to suspend a login shell unless
the parent process is a member of the same terminal session but is
a member of a different process group. As a general rule, if the
shell was started by another shell or via su(1), it can be sus‐
pended.
test expression
[ expression ]
test evaluates the expression and returns zero status if true, 1
if false, or greater than 1 if there was an error. It is normally
used as the condition command of if and while statements. Sym‐
bolic links are followed for all file expressions except -h and
-L.
The following basic expressions are available:
-a file file exists.
-b file file is a block special device.
-c file file is a character special device.
-d file file is a directory.
-e file file exists.
-f file file is a regular file.
-G file file's group is the shell's effective group ID.
-g file file's mode has the setgid bit set.
-H file file is a context dependent directory (only
useful on HP-UX).
-h file file is a symbolic link.
-k file file's mode has the sticky(8) bit set.
-L file file is a symbolic link.
-O file file's owner is the shell's effective user ID.
-o option Shell option is set (see the set command above
for a list of options). As a non-standard
extension, if the option starts with a ‘!’, the
test is negated; the test always fails if
option doesn't exist (so [ -o foo -o -o !foo ]
returns true if and only if option foo exists).
The same can be achieved with [ -o ?foo ] like
in AT&T UNIX ksh93. option can also be the
short flag led by either ‘-’ or ‘+’ (no logical
negation), for example ‘-x’ or ‘+x’ instead of
‘xtrace’.
-p file file is a named pipe (FIFO).
-r file file exists and is readable.
-S file file is a unix(4)-domain socket.
-s file file is not empty.
-t fd File descriptor fd is a tty(4) device.
-u file file's mode has the setuid bit set.
-w file file exists and is writable.
-x file file exists and is executable.
file1 -nt file2 file1 is newer than file2 or file1 exists and
file2 does not.
file1 -ot file2 file1 is older than file2 or file2 exists and
file1 does not.
file1 -ef file2 file1 is the same file as file2.
string string has non-zero length.
-n string string is not empty.
-z string string is empty.
string = string Strings are equal.
string == string Strings are equal.
string > string First string operand is greater than second
string operand.
string < string First string operand is less than second string
operand.
string != string Strings are not equal.
number -eq number Numbers compare equal.
number -ne number Numbers compare not equal.
number -ge number Numbers compare greater than or equal.
number -gt number Numbers compare greater than.
number -le number Numbers compare less than or equal.
number -lt number Numbers compare less than.
The above basic expressions, in which unary operators have prece‐
dence over binary operators, may be combined with the following
operators (listed in increasing order of precedence):
expr -o expr Logical OR.
expr -a expr Logical AND.
! expr Logical NOT.
( expr ) Grouping.
Note that a number actually may be an arithmetic expression, such
as a mathematical term or the name of an integer variable:
x=1; [ "x" -eq 1 ] evaluates to true
Note that some special rules are applied (courtesy of POSIX) if
the number of arguments to test or inside the brackets [ ... ] is
less than five: if leading ‘!’ arguments can be stripped such that
only one to three arguments remain, then the lowered comparison is
executed; (thanks to XSI) parentheses \( ... \) lower four- and
three-argument forms to two- and one-argument forms, respectively;
three-argument forms ultimately prefer binary operations, followed
by negation and parenthesis lowering; two- and four-argument forms
prefer negation followed by parenthesis; the one-argument form
always implies -n.
Note: A common mistake is to use “if [ $foo = bar ]” which fails
if parameter “foo” is NULL or unset, if it has embedded spaces
(i.e. IFS octets), or if it is a unary operator like ‘!’ or ‘-n’.
Use tests like “if [ x"$foo" = x"bar" ]” instead, or the double-
bracket operator “if [[ $foo = bar ]]” or, to avoid pattern match‐
ing (see [[ above): “if [[ $foo = "$bar" ]]”
The [[ ... ]] construct is not only more secure to use but also
often faster.
time [-p] [pipeline]
If a pipeline is given, the times used to execute the pipeline are
reported. If no pipeline is given, then the user and system time
used by the shell itself, and all the commands it has run since it
was started, are reported. The times reported are the real time
(elapsed time from start to finish), the user CPU time (time spent
running in user mode), and the system CPU time (time spent running
in kernel mode). Times are reported to standard error; the format
of the output is:
0m0.00s real 0m0.00s user 0m0.00s system
If the -p option is given the output is slightly longer:
real 0.00
user 0.00
sys 0.00
It is an error to specify the -p option unless pipeline is a sim‐
ple command.
Simple redirections of standard error do not affect the output of
the time command:
$ time sleep 1 2>afile
$ { time sleep 1; } 2>afile
Times for the first command do not go to “afile”, but those of the
second command do.
times Print the accumulated user and system times used both by the shell
and by processes that the shell started which have exited. The
format of the output is:
0m0.00s 0m0.00s
0m0.00s 0m0.00s
trap n [signal ...]
If the first operand is a decimal unsigned integer, this resets
all specified signals to the default action, i.e. is the same as
calling trap with a minus sign (‘-’) as handler, followed by the
arguments (n [signal ...]), all of which are treated as signals.
trap [handler signal ...]
Sets a trap handler that is to be executed when any of the speci‐
fied signals are received. handler is either an empty string,
indicating the signals are to be ignored, a minus sign (‘-’),
indicating that the default action is to be taken for the signals
(see signal(3)), or a string containing shell commands to be exe‐
cuted at the first opportunity (i.e. when the current command com‐
pletes, or before printing the next PS1 prompt) after receipt of
one of the signals. signal is the name of a signal (e.g. PIPE or
ALRM) or the number of the signal (see the kill -l command above).
There are two special signals: EXIT (also known as 0), which is
executed when the shell is about to exit, and ERR, which is exe‐
cuted after an error occurs; an error is something that would
cause the shell to exit if the set -e or set -o errexit option
were set. EXIT handlers are executed in the environment of the
last executed command.
Note that, for non-interactive shells, the trap handler cannot be
changed for signals that were ignored when the shell started.
With no arguments, the current state of the traps that have been
set since the shell started is shown as a series of trap commands.
Note that the output of trap cannot be usefully piped to another
process (an artifact of the fact that traps are cleared when sub‐
processes are created).
The original Korn shell's DEBUG trap and the handling of ERR and
EXIT traps in functions are not yet implemented.
true A command that exits with a zero value.
global [[+-alpnrtUux] [-L[n]] [-R[n]] [-Z[n]] [-i[n]] | -f [-tux]] [name
[=value] ...]
typeset [[+-alpnrtUux] [-LRZ[n]] [-i[n]] | -f [-tux]] [name [=value] ...]
Display or set parameter attributes. With no name arguments,
parameter attributes are displayed; if no options are used, the
current attributes of all parameters are printed as typeset com‐
mands; if an option is given (or ‘-’ with no option letter), all
parameters and their values with the specified attributes are
printed; if options are introduced with ‘+’, parameter values are
not printed.
If name arguments are given, the attributes of the named parame‐
ters are set (-) or cleared (+). Values for parameters may
optionally be specified. For name[*], the change affects the
entire array, and no value may be specified.
If typeset is used inside a function, any parameters specified are
localised. This is not done by the otherwise identical global.
Note: This means that mksh 's global command is not equivalent to
other programming languages' as it does not allow a function
called from another function to access a parameter at truly global
scope, but only prevents putting an accessed one into local scope.
When -f is used, typeset operates on the attributes of functions.
As with parameters, if no name arguments are given, functions are
listed with their values (i.e. definitions) unless options are
introduced with ‘+’, in which case only the function names are
reported.
-a Indexed array attribute.
-f Function mode. Display or set functions and their
attributes, instead of parameters.
-i[n] Integer attribute. n specifies the base to use when dis‐
playing the integer (if not specified, the base given in
the first assignment is used). Parameters with this
attribute may be assigned values containing arithmetic
expressions.
-L[n] Left justify attribute. n specifies the field width. If
n is not specified, the current width of a parameter (or
the width of its first assigned value) is used. Leading
whitespace (and zeros, if used with the -Z option) is
stripped. If necessary, values are either truncated or
space padded to fit the field width.
-l Lower case attribute. All upper case characters in values
are converted to lower case. (In the original Korn shell,
this parameter meant “long integer” when used with the -i
option.)
-n Create a bound variable (name reference): any access to
the variable name will access the variable value in the
current scope (this is different from AT&T UNIX ksh93!)
instead. Also different from AT&T UNIX ksh93 is that
value is lazily evaluated at the time name is accessed.
This can be used by functions to access variables whose
names are passed as parametres, instead of using eval.
-p Print complete typeset commands that can be used to re-
create the attributes and values of parameters.
-R[n] Right justify attribute. n specifies the field width. If
n is not specified, the current width of a parameter (or
the width of its first assigned value) is used. Trailing
whitespace is stripped. If necessary, values are either
stripped of leading characters or space padded to make
them fit the field width.
-r Read-only attribute. Parameters with this attribute may
not be assigned to or unset. Once this attribute is set,
it cannot be turned off.
-t Tag attribute. Has no meaning to the shell; provided for
application use.
For functions, -t is the trace attribute. When functions
with the trace attribute are executed, the xtrace (-x)
shell option is temporarily turned on.
-U Unsigned integer attribute. Integers are printed as
unsigned values (combine with the -i option). This option
is not in the original Korn shell.
-u Upper case attribute. All lower case characters in values
are converted to upper case. (In the original Korn shell,
this parameter meant “unsigned integer” when used with the
-i option which meant upper case letters would never be
used for bases greater than 10. See the -U option.)
For functions, -u is the undefined attribute. See
Functions above for the implications of this.
-x Export attribute. Parameters (or functions) are placed in
the environment of any executed commands. Exported func‐
tions are not yet implemented.
-Z[n] Zero fill attribute. If not combined with -L, this is the
same as -R, except zero padding is used instead of space
padding. For integers, the number instead of the base is
padded.
If any of the -i, -L, -l, -R, -U, -u, or -Z options are changed,
all others from this set are cleared, unless they are also given
on the same command line.
ulimit [-aBCcdefHilMmnOPpqrSsTtVvw] [value]
Display or set process limits. If no options are used, the file
size limit (-f) is assumed. value, if specified, may be either an
arithmetic expression or the word “unlimited”. The limits affect
the shell and any processes created by the shell after a limit is
imposed. Note that some systems may not allow limits to be
increased once they are set. Also note that the types of limits
available are system dependent – some systems have only the -f
limit.
-a Display all limits; unless -H is used, soft limits are dis‐
played.
-B n Set the socket buffer size to n kibibytes.
-C n Set the number of cached threads to n.
-c n Impose a size limit of n blocks on the size of core dumps.
-d n Impose a size limit of n kibibytes on the size of the data
area.
-e n Set the maximum niceness to n.
-f n Impose a size limit of n blocks on files written by the
shell and its child processes (files of any size may be
read).
-H Set the hard limit only (the default is to set both hard
and soft limits).
-i n Set the number of pending signals to n.
-l n Impose a limit of n kibibytes on the amount of locked
(wired) physical memory.
-M n Set the AIO locked memory to n kibibytes.
-m n Impose a limit of n kibibytes on the amount of physical
memory used.
-n n Impose a limit of n file descriptors that can be open at
once.
-O n Set the number of AIO operations to n.
-P n Limit the number of threads per process to n.
-p n Impose a limit of n processes that can be run by the user
at any one time.
-q n Limit the size of POSIX message queues to n bytes.
-r n Set the maximum real-time priority to n.
-S Set the soft limit only (the default is to set both hard
and soft limits).
-s n Impose a size limit of n kibibytes on the size of the stack
area.
-T n Impose a time limit of n real seconds to be used by each
process.
-t n Impose a time limit of n CPU seconds spent in user mode to
be used by each process.
-V n Set the number of vnode monitors on Haiku to n.
-v n Impose a limit of n kibibytes on the amount of virtual mem‐
ory (address space) used.
-w n Impose a limit of n kibibytes on the amount of swap space
used.
As far as ulimit is concerned, a block is 512 bytes.
umask [-S] [mask]
Display or set the file permission creation mask, or umask (see
umask(2)). If the -S option is used, the mask displayed or set is
symbolic; otherwise, it is an octal number.
Symbolic masks are like those used by chmod(1). When used, they
describe what permissions may be made available (as opposed to
octal masks in which a set bit means the corresponding bit is to
be cleared). For example, “ug=rwx,o=” sets the mask so files will
not be readable, writable, or executable by “others”, and is
equivalent (on most systems) to the octal mask “007”.
unalias [-adt] [name ...]
The aliases for the given names are removed. If the -a option is
used, all aliases are removed. If the -t or -d options are used,
the indicated operations are carried out on tracked or directory
aliases, respectively.
unset [-fv] parameter ...
Unset the named parameters (-v, the default) or functions (-f).
With parameter[*], attributes are kept, only values are unset.
The exit status is non-zero if any of the parameters have the
read-only attribute set, zero otherwise.
wait [job ...]
Wait for the specified job(s) to finish. The exit status of wait
is that of the last specified job; if the last job is killed by a
signal, the exit status is 128 + the number of the signal (see
kill -l exit-status above); if the last specified job can't be
found (because it never existed, or had already finished), the
exit status of wait is 127. See Job control below for the format
of job. wait will return if a signal for which a trap has been
set is received, or if a SIGHUP, SIGINT, or SIGQUIT signal is
received.
If no jobs are specified, wait waits for all currently running
jobs (if any) to finish and exits with a zero status. If job mon‐
itoring is enabled, the completion status of jobs is printed (this
is not the case when jobs are explicitly specified).
whence [-pv] [name ...]
For each name, the type of command is listed (reserved word,
built-in, alias, function, tracked alias, or executable). If the
-p option is used, a path search is performed even if name is a
reserved word, alias, etc. Without the -v option, whence is simi‐
lar to command -v except that whence will find reserved words and
won't print aliases as alias commands. With the -v option, whence
is the same as command -V. Note that for whence, the -p option
does not affect the search path used, as it does for command. If
the type of one or more of the names could not be determined, the
exit status is non-zero.
Job control
Job control refers to the shell's ability to monitor and control jobs
which are processes or groups of processes created for commands or pipe‐
lines. At a minimum, the shell keeps track of the status of the back‐
ground (i.e. asynchronous) jobs that currently exist; this information
can be displayed using the jobs commands. If job control is fully
enabled (using set -m or set -o monitor), as it is for interactive
shells, the processes of a job are placed in their own process group.
Foreground jobs can be stopped by typing the suspend character from the
terminal (normally ^Z), jobs can be restarted in either the foreground or
background using the fg and bg commands, and the state of the terminal is
saved or restored when a foreground job is stopped or restarted, respec‐
tively.
Note that only commands that create processes (e.g. asynchronous com‐
mands, subshell commands, and non-built-in, non-function commands) can be
stopped; commands like read cannot be.
When a job is created, it is assigned a job number. For interactive
shells, this number is printed inside “[..]”, followed by the process IDs
of the processes in the job when an asynchronous command is run. A job
may be referred to in the bg, fg, jobs, kill, and wait commands either by
the process ID of the last process in the command pipeline (as stored in
the $! parameter) or by prefixing the job number with a percent sign
(‘%’). Other percent sequences can also be used to refer to jobs:
%+ | %% | % The most recently stopped job, or, if there are no stopped
jobs, the oldest running job.
%- The job that would be the %+ job if the latter did not
exist.
%n The job with job number n.
%?string The job with its command containing the string string (an
error occurs if multiple jobs are matched).
%string The job with its command starting with the string string
(an error occurs if multiple jobs are matched).
When a job changes state (e.g. a background job finishes or foreground
job is stopped), the shell prints the following status information:
[number] flag status command
where...
number is the job number of the job;
flag is the ‘+’ or ‘-’ character if the job is the %+ or %- job,
respectively, or space if it is neither;
status indicates the current state of the job and can be:
Done [number]
The job exited. number is the exit status of the job
which is omitted if the status is zero.
Running The job has neither stopped nor exited (note that
running does not necessarily mean consuming CPU time
– the process could be blocked waiting for some
event).
Stopped [signal]
The job was stopped by the indicated signal (if no
signal is given, the job was stopped by SIGTSTP).
signal-description [“core dumped”]
The job was killed by a signal (e.g. memory fault,
hangup); use kill -l for a list of signal descrip‐
tions. The “core dumped” message indicates the
process created a core file.
command is the command that created the process. If there are multiple
processes in the job, each process will have a line showing its
command and possibly its status, if it is different from the
status of the previous process.
When an attempt is made to exit the shell while there are jobs in the
stopped state, the shell warns the user that there are stopped jobs and
does not exit. If another attempt is immediately made to exit the shell,
the stopped jobs are sent a SIGHUP signal and the shell exits. Simi‐
larly, if the nohup option is not set and there are running jobs when an
attempt is made to exit a login shell, the shell warns the user and does
not exit. If another attempt is immediately made to exit the shell, the
running jobs are sent a SIGHUP signal and the shell exits.
POSIX mode
Entering set -o posix mode will cause mksh to behave even more POSIX com‐
pliant in places where the defaults or opinions differ. Note that mksh
will still operate with unsigned 32-bit arithmetics; use lksh if arith‐
metics on the host long data type, complete with ISO C Undefined Behav‐
iour, are required; refer to the lksh(1) manual page for details. Most
other historic, AT&T UNIX ksh-compatible, or opinionated differences can
be disabled by using this mode; these are:
· The GNU bash I/O redirection &>file is no longer supported.
· File descriptors created by I/O redirections are inherited by child
processes.
· Numbers with a leading digit zero are interpreted as octal.
· The echo builtin does not interpret backslashes and only supports the
exact option “-n”.
· ... (list is incomplete and may change for R53)
SH mode
Compatibility mode; intended for use with legacy scripts that cannot eas‐
ily be fixed; the changes are as follows:
· The GNU bash I/O redirection &>file is no longer supported.
· File descriptors created by I/O redirections are inherited by child
processes.
· The echo builtin does not interpret backslashes and only supports the
exact option “-n”.
· ... (list is incomplete and may change for R53)
Interactive input line editing
The shell supports three modes of reading command lines from a tty(4) in
an interactive session, controlled by the emacs, gmacs, and vi options
(at most one of these can be set at once). The default is emacs. Edit‐
ing modes can be set explicitly using the set built-in. If none of these
options are enabled, the shell simply reads lines using the normal tty(4)
driver. If the emacs or gmacs option is set, the shell allows emacs-like
editing of the command; similarly, if the vi option is set, the shell
allows vi-like editing of the command. These modes are described in
detail in the following sections.
In these editing modes, if a line is longer than the screen width (see
the COLUMNS parameter), a ‘>’, ‘+’, or ‘<’ character is displayed in the
last column indicating that there are more characters after, before and
after, or before the current position, respectively. The line is
scrolled horizontally as necessary.
Completed lines are pushed into the history, unless they begin with an
IFS octet or IFS white space, or are the same as the previous line.
Emacs editing mode
When the emacs option is set, interactive input line editing is enabled.
Warning: This mode is slightly different from the emacs mode in the orig‐
inal Korn shell. In this mode, various editing commands (typically bound
to one or more control characters) cause immediate actions without wait‐
ing for a newline. Several editing commands are bound to particular con‐
trol characters when the shell is invoked; these bindings can be changed
using the bind command.
The following is a list of available editing commands. Each description
starts with the name of the command, suffixed with a colon; an [n] (if
the command can be prefixed with a count); and any keys the command is
bound to by default, written using caret notation e.g. the ASCII ESC
character is written as ^[. These control sequences are not case sensi‐
tive. A count prefix for a command is entered using the sequence ^[n,
where n is a sequence of 1 or more digits. Unless otherwise specified,
if a count is omitted, it defaults to 1.
Note that editing command names are used only with the bind command.
Furthermore, many editing commands are useful only on terminals with a
visible cursor. The default bindings were chosen to resemble correspond‐
ing Emacs key bindings. The user's tty(4) characters (e.g. ERASE) are
bound to reasonable substitutes and override the default bindings.
abort: ^C, ^G
Abort the current command, empty the line buffer and set the exit
state to interrupted.
auto-insert: [n]
Simply causes the character to appear as literal input. Most
ordinary characters are bound to this.
backward-char: [n] ^B, ^XD, ANSI-CurLeft, PC-CurLeft
Moves the cursor backward n characters.
backward-word: [n] ^[b, ANSI-Ctrl-CurLeft, ANSI-Alt-CurLeft
Moves the cursor backward to the beginning of the word; words
consist of alphanumerics, underscore (‘_’), and dollar sign (‘$’)
characters.
beginning-of-history: ^[<
Moves to the beginning of the history.
beginning-of-line: ^A, ANSI-Home, PC-Home
Moves the cursor to the beginning of the edited input line.
capitalise-word: [n] ^[C, ^[c
Uppercase the first character in the next n words, leaving the
cursor past the end of the last word.
clear-screen: ^[^L
Prints a compile-time configurable sequence to clear the screen
and home the cursor, redraws the entire prompt and the currently
edited input line. The default sequence works for almost all
standard terminals.
comment: ^[#
If the current line does not begin with a comment character, one
is added at the beginning of the line and the line is entered (as
if return had been pressed); otherwise, the existing comment
characters are removed and the cursor is placed at the beginning
of the line.
complete: ^[^[
Automatically completes as much as is unique of the command name
or the file name containing the cursor. If the entire remaining
command or file name is unique, a space is printed after its com‐
pletion, unless it is a directory name in which case ‘/’ is
appended. If there is no command or file name with the current
partial word as its prefix, a bell character is output (usually
causing a beep to be sounded).
complete-command: ^X^[
Automatically completes as much as is unique of the command name
having the partial word up to the cursor as its prefix, as in the
complete command above.
complete-file: ^[^X
Automatically completes as much as is unique of the file name
having the partial word up to the cursor as its prefix, as in the
complete command described above.
complete-list: ^I, ^[=
Complete as much as is possible of the current word, and list the
possible completions for it. If only one completion is possible,
match as in the complete command above. Note that ^I is usually
generated by the TAB (tabulator) key.
delete-char-backward: [n] ERASE, ^?, ^H
Deletes n characters before the cursor.
delete-char-forward: [n] ANSI-Del, PC-Del
Deletes n characters after the cursor.
delete-word-backward: [n] WERASE, ^[^?, ^[^H, ^[h
Deletes n words before the cursor.
delete-word-forward: [n] ^[d
Deletes characters after the cursor up to the end of n words.
down-history: [n] ^N, ^XB, ANSI-CurDown, PC-CurDown
Scrolls the history buffer forward n lines (later). Each input
line originally starts just after the last entry in the history
buffer, so down-history is not useful until either
search-history, search-history-up or up-history has been per‐
formed.
downcase-word: [n] ^[L, ^[l
Lowercases the next n words.
edit-line: [n] ^Xe
Edit line n or the current line, if not specified, interactively.
The actual command executed is fc -e ${VISUAL:-${EDITOR:-vi}} n.
end-of-history: ^[>
Moves to the end of the history.
end-of-line: ^E, ANSI-End, PC-End
Moves the cursor to the end of the input line.
eot: ^_
Acts as an end-of-file; this is useful because edit-mode input
disables normal terminal input canonicalization.
eot-or-delete: [n] ^D
Acts as eot if alone on a line; otherwise acts as
delete-char-forward.
error: (not bound)
Error (ring the bell).
exchange-point-and-mark: ^X^X
Places the cursor where the mark is and sets the mark to where
the cursor was.
expand-file: ^[*
Appends a ‘*’ to the current word and replaces the word with the
result of performing file globbing on the word. If no files
match the pattern, the bell is rung.
forward-char: [n] ^F, ^XC, ANSI-CurRight, PC-CurRight
Moves the cursor forward n characters.
forward-word: [n] ^[f, ANSI-Ctrl-CurRight, ANSI-Alt-CurRight
Moves the cursor forward to the end of the nth word.
goto-history: [n] ^[g
Goes to history number n.
kill-line: KILL
Deletes the entire input line.
kill-region: ^W
Deletes the input between the cursor and the mark.
kill-to-eol: [n] ^K
Deletes the input from the cursor to the end of the line if n is
not specified; otherwise deletes characters between the cursor
and column n.
list: ^[?
Prints a sorted, columnated list of command names or file names
(if any) that can complete the partial word containing the cur‐
sor. Directory names have ‘/’ appended to them.
list-command: ^X?
Prints a sorted, columnated list of command names (if any) that
can complete the partial word containing the cursor.
list-file: ^X^Y
Prints a sorted, columnated list of file names (if any) that can
complete the partial word containing the cursor. File type indi‐
cators are appended as described under list above.
newline: ^J, ^M
Causes the current input line to be processed by the shell. The
current cursor position may be anywhere on the line.
newline-and-next: ^O
Causes the current input line to be processed by the shell, and
the next line from history becomes the current line. This is
only useful after an up-history, search-history or
search-history-up.
no-op: QUIT
This does nothing.
prefix-1: ^[
Introduces a 2-character command sequence.
prefix-2: ^X, ^[[, ^[O
Introduces a 2-character command sequence.
prev-hist-word: [n] ^[., ^[_
The last word, or, if given, the nth word (zero-based) of the
previous (on repeated execution, second-last, third-last, etc.)
command is inserted at the cursor. Use of this editing command
trashes the mark.
quote: ^^, ^V
The following character is taken literally rather than as an
editing command.
redraw: ^L
Reprints the last line of the prompt string and the current input
line on a new line.
search-character-backward: [n] ^[^]
Search backward in the current line for the nth occurrence of the
next character typed.
search-character-forward: [n] ^]
Search forward in the current line for the nth occurrence of the
next character typed.
search-history: ^R
Enter incremental search mode. The internal history list is
searched backwards for commands matching the input. An initial
‘^’ in the search string anchors the search. The escape key will
leave search mode. Other commands, including sequences of escape
as prefix-1 followed by a prefix-1 or prefix-2 key will be exe‐
cuted after leaving search mode. The abort (^G) command will
restore the input line before search started. Successive
search-history commands continue searching backward to the next
previous occurrence of the pattern. The history buffer retains
only a finite number of lines; the oldest are discarded as neces‐
sary.
search-history-up: ANSI-PgUp, PC-PgUp
Search backwards through the history buffer for commands whose
beginning match the portion of the input line before the cursor.
When used on an empty line, this has the same effect as
up-history.
search-history-down: ANSI-PgDn, PC-PgDn
Search forwards through the history buffer for commands whose
beginning match the portion of the input line before the cursor.
When used on an empty line, this has the same effect as
down-history. This is only useful after an up-history,
search-history or search-history-up.
set-mark-command: ^[<space>
Set the mark at the cursor position.
transpose-chars: ^T
If at the end of line, or if the gmacs option is set, this
exchanges the two previous characters; otherwise, it exchanges
the previous and current characters and moves the cursor one
character to the right.
up-history: [n] ^P, ^XA, ANSI-CurUp, PC-CurUp
Scrolls the history buffer backward n lines (earlier).
upcase-word: [n] ^[U, ^[u
Uppercase the next n words.
version: ^[^V
Display the version of mksh. The current edit buffer is restored
as soon as a key is pressed. The restoring keypress is pro‐
cessed, unless it is a space.
yank: ^Y
Inserts the most recently killed text string at the current cur‐
sor position.
yank-pop: ^[y
Immediately after a yank, replaces the inserted text string with
the next previously killed text string.
Vi editing mode
Note: The vi command-line editing mode is orphaned, yet still functional.
It is 8-bit clean but specifically does not support UTF-8 or MBCS.
The vi command-line editor in mksh has basically the same commands as the
vi(1) editor with the following exceptions:
· You start out in insert mode.
· There are file name and command completion commands: =, \, *, ^X, ^E,
^F, and, optionally, <tab> and <esc>.
· The _ command is different (in mksh, it is the last argument command;
in vi(1) it goes to the start of the current line).
· The / and G commands move in the opposite direction to the j command.
· Commands which don't make sense in a single line editor are not
available (e.g. screen movement commands and ex(1)-style colon (:)
commands).
Like vi(1), there are two modes: “insert” mode and “command” mode. In
insert mode, most characters are simply put in the buffer at the current
cursor position as they are typed; however, some characters are treated
specially. In particular, the following characters are taken from cur‐
rent tty(4) settings (see stty(1)) and have their usual meaning (normal
values are in parentheses): kill (^U), erase (^?), werase (^W), eof (^D),
intr (^C), and quit (^\). In addition to the above, the following char‐
acters are also treated specially in insert mode:
^E Command and file name enumeration (see below).
^F Command and file name completion (see below). If used twice in
a row, the list of possible completions is displayed; if used a
third time, the completion is undone.
^H Erases previous character.
^J | ^M End of line. The current line is read, parsed, and executed by
the shell.
^V Literal next. The next character typed is not treated specially
(can be used to insert the characters being described here).
^X Command and file name expansion (see below).
<esc> Puts the editor in command mode (see below).
<tab> Optional file name and command completion (see ^F above),
enabled with set -o vi-tabcomplete.
In command mode, each character is interpreted as a command. Characters
that don't correspond to commands, are illegal combinations of commands,
or are commands that can't be carried out, all cause beeps. In the fol‐
lowing command descriptions, an [n] indicates the command may be prefixed
by a number (e.g. 10l moves right 10 characters); if no number prefix is
used, n is assumed to be 1 unless otherwise specified. The term “current
position” refers to the position between the cursor and the character
preceding the cursor. A “word” is a sequence of letters, digits, and
underscore characters or a sequence of non-letter, non-digit, non-under‐
score, and non-whitespace characters (e.g. “ab2*&^” contains two words)
and a “big-word” is a sequence of non-whitespace characters.
Special mksh vi commands:
The following commands are not in, or are different from, the normal vi
file editor:
[n]_ Insert a space followed by the nth big-word from the last
command in the history at the current position and enter
insert mode; if n is not specified, the last word is
inserted.
# Insert the comment character (‘#’) at the start of the cur‐
rent line and return the line to the shell (equivalent to
I#^J).
[n]g Like G, except if n is not specified, it goes to the most
recent remembered line.
[n]v Edit line n using the vi(1) editor; if n is not specified,
the current line is edited. The actual command executed is
fc -e ${VISUAL:-${EDITOR:-vi}} n.
* and ^X Command or file name expansion is applied to the current big-
word (with an appended ‘*’ if the word contains no file glob‐
bing characters) – the big-word is replaced with the result‐
ing words. If the current big-word is the first on the line
or follows one of the characters ‘;’, ‘|’, ‘&’, ‘(’, or ‘)’,
and does not contain a slash (‘/’), then command expansion is
done; otherwise file name expansion is done. Command expan‐
sion will match the big-word against all aliases, functions,
and built-in commands as well as any executable files found
by searching the directories in the PATH parameter. File
name expansion matches the big-word against the files in the
current directory. After expansion, the cursor is placed
just past the last word and the editor is in insert mode.
[n]\, [n]^F, [n]<tab>, and [n]<esc>
Command/file name completion. Replace the current big-word
with the longest unique match obtained after performing com‐
mand and file name expansion. <tab> is only recognised if
the vi-tabcomplete option is set, while <esc> is only recog‐
nised if the vi-esccomplete option is set (see set -o). If n
is specified, the nth possible completion is selected (as
reported by the command/file name enumeration command).
= and ^E Command/file name enumeration. List all the commands or
files that match the current big-word.
^V Display the version of mksh. The current edit buffer is
restored as soon as a key is pressed. The restoring keypress
is ignored.
@c Macro expansion. Execute the commands found in the alias c.
Intra-line movement commands:
[n]h and [n]^H
Move left n characters.
[n]l and [n]<space>
Move right n characters.
0 Move to column 0.
^ Move to the first non-whitespace character.
[n]| Move to column n.
$ Move to the last character.
[n]b Move back n words.
[n]B Move back n big-words.
[n]e Move forward to the end of the word, n times.
[n]E Move forward to the end of the big-word, n times.
[n]w Move forward n words.
[n]W Move forward n big-words.
% Find match. The editor looks forward for the nearest parenthe‐
sis, bracket, or brace and then moves the cursor to the matching
parenthesis, bracket, or brace.
[n]fc Move forward to the nth occurrence of the character c.
[n]Fc Move backward to the nth occurrence of the character c.
[n]tc Move forward to just before the nth occurrence of the character
c.
[n]Tc Move backward to just before the nth occurrence of the character
c.
[n]; Repeats the last f, F, t, or T command.
[n], Repeats the last f, F, t, or T command, but moves in the opposite
direction.
Inter-line movement commands:
[n]j, [n]+, and [n]^N
Move to the nth next line in the history.
[n]k, [n]-, and [n]^P
Move to the nth previous line in the history.
[n]G Move to line n in the history; if n is not specified, the number
of the first remembered line is used.
[n]g Like G, except if n is not specified, it goes to the most recent
remembered line.
[n]/string
Search backward through the history for the nth line containing
string; if string starts with ‘^’, the remainder of the string
must appear at the start of the history line for it to match.
[n]?string
Same as /, except it searches forward through the history.
[n]n Search for the nth occurrence of the last search string; the
direction of the search is the same as the last search.
[n]N Search for the nth occurrence of the last search string; the
direction of the search is the opposite of the last search.
ANSI-CurUp, PC-PgUp
Take the characters from the beginning of the line to the current
cursor position as search string and do a backwards history
search for lines beginning with this string; keep the cursor
position. This works only in insert mode and keeps it enabled.
Edit commands
[n]a Append text n times; goes into insert mode just after the current
position. The append is only replicated if command mode is re-
entered i.e. <esc> is used.
[n]A Same as a, except it appends at the end of the line.
[n]i Insert text n times; goes into insert mode at the current posi‐
tion. The insertion is only replicated if command mode is re-
entered i.e. <esc> is used.
[n]I Same as i, except the insertion is done just before the first
non-blank character.
[n]s Substitute the next n characters (i.e. delete the characters and
go into insert mode).
S Substitute whole line. All characters from the first non-blank
character to the end of the line are deleted and insert mode is
entered.
[n]cmove-cmd
Change from the current position to the position resulting from n
move-cmds (i.e. delete the indicated region and go into insert
mode); if move-cmd is c, the line starting from the first non-
blank character is changed.
C Change from the current position to the end of the line (i.e.
delete to the end of the line and go into insert mode).
[n]x Delete the next n characters.
[n]X Delete the previous n characters.
D Delete to the end of the line.
[n]dmove-cmd
Delete from the current position to the position resulting from n
move-cmds; move-cmd is a movement command (see above) or d, in
which case the current line is deleted.
[n]rc Replace the next n characters with the character c.
[n]R Replace. Enter insert mode but overwrite existing characters
instead of inserting before existing characters. The replacement
is repeated n times.
[n]~ Change the case of the next n characters.
[n]ymove-cmd
Yank from the current position to the position resulting from n
move-cmds into the yank buffer; if move-cmd is y, the whole line
is yanked.
Y Yank from the current position to the end of the line.
[n]p Paste the contents of the yank buffer just after the current
position, n times.
[n]P Same as p, except the buffer is pasted at the current position.
Miscellaneous vi commands
^J and ^M
The current line is read, parsed, and executed by the shell.
^L and ^R
Redraw the current line.
[n]. Redo the last edit command n times.
u Undo the last edit command.
U Undo all changes that have been made to the current line.
PC Home, End, Del, and cursor keys
They move as expected, both in insert and command mode.
intr and quit
The interrupt and quit terminal characters cause the current line
to be deleted and a new prompt to be printed.
FILES
~/.mkshrc User mkshrc profile (non-privileged interactive
shells); see Startup files. The location can be
changed at compile time (for embedded systems); AOSP
Android builds use /system/etc/mkshrc.
~/.profile User profile (non-privileged login shells); see
Startup files near the top of this manual.
/etc/profile System profile (login shells); see Startup files.
/etc/shells Shell database.
/etc/suid_profile Suid profile (privileged shells); see Startup files.
Note: On Android, /system/etc/ contains the system and suid profile.
SEE ALSO
awk(1), cat(1), ed(1), getopt(1), lksh(1), sed(1), sh(1), stty(1),
dup(2), execve(2), getgid(2), getuid(2), mknod(2), mkfifo(2), open(2),
pipe(2), rename(2), wait(2), getopt(3), nl_langinfo(3), setlocale(3),
signal(3), system(3), tty(4), shells(5), environ(7), script(7), utf-8(7),
mknod(8)
https://www.mirbsd.org/ksh-chan.htm
Morris Bolsky, The KornShell Command and Programming Language, Prentice
Hall PTR, xvi + 356 pages, 1989, ISBN 978-0-13-516972-8 (0-13-516972-0).
Morris I. Bolsky and David G. Korn, The New KornShell Command and
Programming Language (2nd Edition), Prentice Hall PTR, xvi + 400 pages,
1995, ISBN 978-0-13-182700-4 (0-13-182700-6).
Stephen G. Kochan and Patrick H. Wood, UNIX Shell Programming, Sams, 3rd
Edition, xiii + 437 pages, 2003, ISBN 978-0-672-32490-1 (0-672-32490-3).
IEEE Inc., IEEE Standard for Information Technology – Portable Operating
System Interface (POSIX), IEEE Press, Part 2: Shell and Utilities,
xvii + 1195 pages, 1993, ISBN 978-1-55937-255-8 (1-55937-255-9).
Bill Rosenblatt, Learning the Korn Shell, O'Reilly, 360 pages, 1993, ISBN
978-1-56592-054-5 (1-56592-054-6).
Bill Rosenblatt and Arnold Robbins, Learning the Korn Shell, Second
Edition, O'Reilly, 432 pages, 2002, ISBN 978-0-596-00195-7
(0-596-00195-9).
Barry Rosenberg, KornShell Programming Tutorial, Addison-Wesley
Professional, xxi + 324 pages, 1991, ISBN 978-0-201-56324-5
(0-201-56324-X).
AUTHORS
The MirBSD Korn Shell is developed by mirabilos <m@mirbsd.org> as part of
The MirOS Project. This shell is based on the public domain 7th edition
Bourne shell clone by Charles Forsyth, who kindly agreed to, in countries
where the Public Domain status of the work may not be valid, grant a
copyright licence to the general public to deal in the work without
restriction and permission to sublicence derivates under the terms of any
(OSI approved) Open Source licence, and parts of the BRL shell by Doug A.
Gwyn, Doug Kingston, Ron Natalie, Arnold Robbins, Lou Salkind, and oth‐
ers. The first release of pdksh was created by Eric Gisin, and it was
subsequently maintained by John R. MacMillan, Simon J. Gerraty, and
Michael Rendell. The effort of several projects, such as Debian and
OpenBSD, and other contributors including our users, to improve the shell
is appreciated. See the documentation, CVS, and web site for details.
The BSD daemon is Copyright © Marshall Kirk McKusick. The complete
legalese is at: https://www.mirbsd.org/TaC-mksh.txt
CAVEATS
mksh has a different scope model from AT&T UNIX ksh, which leads to sub‐
tile differences in semantics for identical builtins. This can cause
issues with a nameref to suddenly point to a local variable by accident;
fixing this is hard.
The parts of a pipeline, like below, are executed in subshells. Thus,
variable assignments inside them are not visible in the surrounding exe‐
cution environment. Use co-processes instead.
foo | bar | read baz # will not change $baz
foo | bar |& read -p baz # will, however, do so
mksh provides a consistent set of 32-bit integer arithmetics, both signed
and unsigned, with defined wraparound and sign of the result of a remain‐
der operation, even (defying POSIX) on 36-bit and 64-bit systems.
mksh provides a consistent, clear interface normally. This may deviate
from POSIX in historic or opinionated places. set -o posix (see POSIX
mode for details) will cause the shell to behave more conformant.
For the purpose of POSIX, mksh supports only the “C” locale. mksh's
utf8-mode only supports the Unicode BMP (Basic Multilingual Plane) and
maps raw octets into the U+EF80..U+EFFF wide character range; compare
Arithmetic expressions. The following POSIX sh code toggles the
utf8-mode option dependent on the current POSIX locale for mksh to allow
using the UTF-8 mode, within the constraints outlined above, in code por‐
table across various shell implementations:
case ${KSH_VERSION:-} in
*MIRBSD KSH*|*LEGACY KSH*)
case ${LC_ALL:-${LC_CTYPE:-${LANG:-}}} in
*[Uu][Tt][Ff]8*|*[Uu][Tt][Ff]-8*) set -U ;;
*) set +U ;;
esac ;;
esac
In near future, (Unicode) locale tracking will be implemented though.
BUGS
Suspending (using ^Z) pipelines like the one below will only suspend the
currently running part of the pipeline; in this example, “fubar” is imme‐
diately printed on suspension (but not later after an fg).
$ /bin/sleep 666 && echo fubar
The truncation process involved when changing HISTFILE does not free old
history entries (leaks memory) and leaks old entries into the new history
if their line numbers are not overwritten by same-numer entries from the
persistent history file; truncating the on-disc file to HISTSIZE lines
has always been broken and prone to history file corruption when multiple
shells are accessing the file; the rollover process for the in-memory
portion of the history is slow, should use memmove(3).
Handling of backslash plus double-quote inside the (deprecated) `command`
form of command substitution when the substitution itself is also inside
double quotes currently deliberately violates POSIX even in -o posix mode
until Austin group bug 1015 has been resolved either way, as the current
wording of the standard prohibits the current and historic practice of
several shells which several scripts (admittedly wrongly) depend on.
This document attempts to describe mksh R52b and up, compiled without any
options impacting functionality, such as MKSH_SMALL, when not called as
/bin/sh which, on some systems only, enables set -o posix or set -o sh
automatically (whose behaviour differs across targets), for an operating
environment supporting all of its advanced needs.
Please report bugs in mksh to the MirOS mailing list at
<miros-mksh@mirbsd.org> or in the #!/bin/mksh (or #ksh) IRC channel at
irc.freenode.net (Port 6697 SSL, 6667 unencrypted), or at:
https://launchpad.net/mksh
MirBSD January 20, 2016 MirBSD
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