ksh88(1)

ksh88, rksh -- KornShell, a standard/restricted command and programming language

Synopsis

ksh88 [±aefhikmnprstuvx] [±o option] . . . [-c string] [arg . . .

rksh [±aefhikmnprstuvx] [±o option] . . . [-c string] [arg . . .

Description

ksh88 is a command and programming language that executes commands read from a terminal, or from a file specified by the current ENV variable when ksh88 is called. rksh is a restricted version of the command interpreter ksh88; it is used to set up login names and execution environments whose capabilities are more controlled than those of the standard shell. See ``Invocation'' for the meaning of arguments to the shell.

Definitions

A metacharacter is one of the following characters:

; & ( ) | < > newline space tab

A blank is a tab or a space. An identifier is a sequence of letters, digits, or underscores starting with a letter or underscore. Identifiers are used as names for functions and variables. A word is a sequence of characters separated by one or more non-quoted metacharacters.

A command is a sequence of characters in the syntax of the shell language. The shell reads each command and carries out the desired action either directly or by invoking separate utilities. A special command is a command that is carried out by the shell without creating a separate process. Except for documented side effects, most special commands can be implemented as separate utilities.

Commands

A simple-command is a sequence of blank-separated words which may be preceded by a variable assignment list (see ``Environment'' ). The first word specifies the name of the command to be executed. Except as specified below, the remaining words are passed as arguments to the invoked command. The command name is passed as argument 0 (see exec(2)). The value of a simple-command is its exit status if it terminates normally, or (octal) 200+status if it terminates abnormally (see signal(2) for a list of status values).

A pipeline is a sequence of one or more commands separated by ``|''. The standard output of each command but the last is connected by a pipe(2) to the standard input of the next command. Each command is run as a separate process; the shell waits for the last command to terminate. The exit status of a pipeline is the exit status of the last command.

A list is a sequence of one or more pipelines separated by ``;'', ``&'', ``&&'', or ``||'', and optionally terminated by ``;'', ``&'', or ``|&''. Of these five symbols, ``;'', ``&'', and ``|&'' have equal precedence, which is lower than that of ``&&'' and ``||''. The symbols ``&&'' and ``||'' also have equal precedence. A semicolon (;) causes sequential execution of the preceding pipeline; an ampersand (``&'') causes asynchronous execution of the preceding pipeline (that is, the shell does not wait for that pipeline to finish). The symbol ``|&'' causes asynchronous execution of the preceding command or pipeline with a two-way pipe established to the parent shell. The standard input and output of the spawned command can be written to and read from by the parent shell using the -p option of the special commands read and print described later. The symbol ``&&'' (``||'') causes the list following it to be executed only if the preceding pipeline returns a zero (non-zero) value. An arbitrary number of newlines may appear in a list, instead of a semicolon, to delimit a command.

A command is either a simple-command or one of the following. Unless otherwise stated, the value returned by a command is that of the last simple-command executed in the command.

for identifier [ in word . . . ] ; do list ; done: Each time a for command is executed, identifier is set to the next word taken from the in word list. If in word ... is omitted, then the for command executes the do list once for each positional parameter that is set (see ``Parameter substitution'' below). Execution ends when there are no more words in the list.
select identifier [ in word . . . ] ; do list ; done: A select command prints on standard error (file descriptor 2), the set of words, each preceded by a number. If in word ... is omitted, then the positional parameters are used instead (see ``Parameter substitution''). The PS3 prompt is printed and a line is read from the standard input. If this line consists of the number of one of the listed words, then the value of the parameter identifier is set to the word corresponding to this number. If this line is empty the selection list is printed again. Otherwise the value of the parameter identifier is set to null. The contents of the line read from standard input is saved in the variable REPLY. The list is executed for each selection until a break or end-of-file is encountered.
case word in [ [(]pattern [ | pattern ] . . . ) list ;; ] . . . esac: A case command executes the list associated with the first pattern that matches word. The form of the patterns is the same as that used for file-name generation (see ``Filename generation'').
if list ;then list [ elif list ;then list ] . . . [ ;else list ] ;fi: The list following if is executed and, if it returns a zero exit status, the list following the first then is executed. Otherwise, the list following elif is executed and, if its value is zero, the list following the next then is executed. Failing that, the else list is executed. If no else list or then list is executed, then the if command returns a zero exit status.
while list ;do list ;done
until list ;do list ;done: A while command repeatedly executes the while list and, if the exit status of the last command in the list is zero, executes the do list; otherwise the loop terminates. If no commands in the do list are executed, then the while command returns a zero exit status; until may be used in place of while to negate the loop termination test.
(list): Execute list in a separate environment. Note, that if two adjacent open parentheses are needed for nesting, a space must be inserted to avoid arithmetic evaluation as described below.
{ list;}: list is simply executed. The { must be followed by a space. Note that unlike the metacharacters ``('' and ``)'', ``{'' and ``}'' are reserved words and must be typed at the beginning of a line or after a ``;'' in order to be recognized.
[[expression]]: Evaluates expression and returns a zero exit status when expression is true. See ``Conditional expressions'' for a description of expression.
function identifier { list ;}
identifier () { list ;}: Define a function which is referenced by identifier. The body of the function is the list of commands between { and }. (see ``Functions''). The { must be followed by a space.
time pipeline: The pipeline is executed and the elapsed time as well as the user and system time are printed on standard error.

The following reserved words are only recognized as the first word of a command and when not quoted:

if then else elif fi case esac for while
until do done { } function select time [[]]

Comments

A word beginning with ``#'' causes that word and all the following characters up to a newline to be ignored.

Aliasing

The first word of each command is replaced by the text of an alias if an alias for this word has been defined. An alias name consists of any number of characters excluding meta-characters, quoting characters, file expansion characters, parameter and command substitution characters and ``=''. The replacement string can contain any valid shell script including the metacharacters listed above. The first word of each command in the replaced text, other than any that are in the process of being replaced, will be tested for aliases. If the last character of the alias value is a blank then the word following the alias will also be checked for alias substitution. Aliases can be used to redefine special builtin commands but cannot be used to redefine the reserved words listed above. Aliases can be created, listed, and exported with the alias command and can be removed with the unalias command. Exported aliases remain in effect for scripts invoked by name, but must be reinitialized for separate invocations of the shell (see ``Invocation'' below).

Aliasing is performed when scripts are read, not while they are executed. Therefore, for an alias to take effect the alias definition command has to be executed before the command which references the alias is read.

Aliases are frequently used as a short hand for full path names. An option to the aliasing facility allows the value of the alias to be automatically set to the full pathname of the corresponding command. These aliases are called tracked aliases. The value of a tracked alias is defined the first time the corresponding command is looked up and becomes undefined each time the PATH variable is reset. These aliases remain tracked so that the next subsequent reference will redefine the value.

Several tracked aliases are compiled into the shell. The -h option of the set command makes each referenced command name into a tracked alias.

The following exported aliases are compiled into the shell but can be unset or redefined:

autoload='typeset -fu'
false='let 0'
functions='typeset -f'
hash='alias -t'
history='fc -l'
integer='typeset -i'
nohup='nohup '
r='fc -e -'
true=':'
type='whence -v'

Tilde substitution

After alias substitution is performed, each word is checked to see if it begins with an unquoted ``~''. If it does, then the word up to a / is checked to see if it matches a user name in the /etc/passwd file. If a match is found, the ``~'' and the matched login name is replaced by the login directory of the matched user. This is called a tilde substitution. If no match is found, the original text is left unchanged. A ``~'' by itself, or in front of a ``/'', is replaced by $HOME. A ``~'' followed by a ``+'' or ``-'' is replaced by $PWD and $OLDPWD respectively.

In addition, tilde substitution is attempted when the value of a variable assignment begins with a ``~''.

Command substitution

The standard output from a command enclosed in parentheses preceded by a dollar sign ($()) or a pair of backquotes (``) may be used as part or all of a word; trailing newlines are removed. In the second (archaic) form, the string between the quotes is processed for special quoting characters before the command is executed (see Quoting below). The command substitution $(cat file) can be replaced by the equivalent but faster $(<file). Command substitution of most special commands that do not perform input/output redirection are carried out without creating a separate process.

An arithmetic expression enclosed in double parentheses and preceded by a dollar sign ($(())) is replaced by the value of the arithmetic expression within the double parentheses.

Parameter substitution

A parameter is an identifier, one or more digits, or any of the characters ``

'', ``@'', ``#'', ``?'', ``-'', ``$'', and ``!''. A variable (a parameter denoted by an identifier) has a value and zero or more attributes. Variables can be assigned values and attributes by using the typeset special command. The attributes supported by the shell are described later with the typeset special command. Exported parameters pass values and attributes to the environment.

The shell supports a one-dimensional array facility. An element of an array variable is referenced by a subscript. A subscript is denoted by a ``['', followed by an arithmetic expression (see ``Arithmetic evaluation'') followed by a ``]''. To assign values to an array, use set -A name value ... The value of all subscripts must be in the range of 0 through 1023. Arrays need not be declared. Any reference to a variable with a valid subscript is legal and an array will be created if necessary. Referencing an array without a subscript is equivalent to referencing the element zero.

The value of a variable may also be assigned by writing:

name=value [name=value] ...

If the integer attribute, -i, is set for name the value is subject to arithmetic evaluation as described below.

Positional parameters, parameters denoted by a number, may be assigned values with the set special command. Parameter $0 is set from argument zero when the shell is invoked.

The character $ is used to introduce substitutable parameters.

${parameter}: The shell reads all the characters from ${ to the matching } as part of the same word even if it contains braces or metacharacters. The value, if any, of the parameter is substituted. The braces are required when parameter is followed by a letter, digit, or underscore that is not to be interpreted as part of its name or when a variable is subscripted. If parameter is one or more digits then it is a positional parameter. A positional parameter of more than one digit must be enclosed in braces. If parameter is or @, then all the positional parameters, starting with $1, are substituted (separated by a field separator character). If an array identifier with subscript ``'' or ``@'' is used, then the value for each of the elements is substituted (separated by a field separator character).
${#parameter}: If parameter is or @, the number of positional parameters is substituted. Otherwise, the length of the value of the parameter is substituted.
${#identifier[*]}: The number of elements in the array identifier is substituted.
${parameter:-word}: If parameter is set and is non-null then substitute its value; otherwise substitute word.
${parameter:=word}: If parameter is not set or is null then set it to word; the value of the parameter is then substituted. Positional parameters may not be assigned to in this way.
${parameter:?word}: If parameter is set and is non-null then substitute its value; otherwise, print word and exit from the shell. If word is omitted then a standard message is printed.
${parameter:+word}: If parameter is set and is non-null then substitute word; otherwise substitute nothing.
${parameter#pattern}
${parameter##pattern}: If the shell pattern matches the beginning of the value of parameter, then the value of this substitution is the value of the parameter with the matched portion deleted; otherwise the value of this parameter is substituted. In the first form the smallest matching pattern is deleted and in the second form the largest matching pattern is deleted.
${parameter%pattern}
${parameter%%pattern}: If the shell pattern matches the end of the value of parameter, then the value of this substitution is the value of the parameter with the matched part deleted; otherwise substitute the value of parameter. In the first form the smallest matching pattern is deleted and in the second form the largest matching pattern is deleted.

In the above, word is not evaluated unless it is to be used as the substituted string, so that, in the following example, pwd is executed only if d is not set or is null:

echo ${d:-$(pwd)}

If the colon (:) is omitted from the above expressions, then the shell only checks whether parameter is set or not.

The following parameters are automatically set by the shell:

#: The number of positional parameters in decimal.
-: Flags supplied to the shell on invocation or by the set command.
?: The decimal value returned by the last executed command.
$: The process number of this shell.
_: Initially, the value _ is an absolute pathname of the shell or script being executed as passed in the environment. Subsequently it is assigned the last argument of the previous command. This parameter is not set for commands which are asynchronous. This parameter is also used to hold the name of the matching MAIL file when checking for mail.
!: The process number of the last background command invoked.
ERRNO: The value of errno as set by the most recently failed system call. This value is system dependent and is intended for debugging purposes.
LINENO: The line number of the current line within the script or function being executed.
OLDPWD: The previous working directory set by the cd command.
OPTARG: The value of the last option argument processed by the getopts special command.
OPTIND: The index of the last option argument processed by the getopts special command.
PPID: The process number of the parent of the shell.
PWD: The present working directory set by the cd command. Each time this variable is referenced, a random integer, uniformly distributed between 0 and 32767, is generated. The sequence of random numbers can be initialized by assigning a numeric value to RANDOM.
REPLY: This variable is set by the select statement and by the read special command when no arguments are supplied.
SECONDS: Each time this variable is referenced, the number of seconds since shell invocation is returned. If this variable is assigned a value, then the value returned upon reference will be the value that was assigned plus the number of seconds since the assignment.

The following variables are used by the shell:

CDPATH: The search path for the cd command.
COLUMNS: If this variable is set, the value is used to define the width of the edit window for the shell edit modes and for printing select lists.
EDITOR: If the value of this variable ends in ``gmacs'', or ``vi'' and the VISUAL variable is not set, then the corresponding option (see set in ``Special commands'') will be turned on.
ENV: If this variable is set, then parameter substitution is performed on the value to generate the pathname of the script that will be executed when the shell is invoked (see ``Invocation'' below). This file is typically used for alias and function definitions.
FCEDIT: The default editor name for the fc command.
FPATH: The search path for function definitions. This path is searched when a function with the -u attribute is referenced and when a command is not found. If an executable file is found, then it is read and executed in the current environment.
IFS: Internal field separators--normally space, tab, and newline--used to separate command words that result from command or parameter substitution and for separating words with the special command read. The first character of the IFS variable is used to separate arguments for the ``"$"'' substitution (see ``Quoting'').
HISTFILE: If this variable is set when the shell is invoked, then the value is the pathname of the file that will be used to store the command history (see ``Command re-entry'').
HISTSIZE: If this variable is set when the shell is invoked, then the number of previously entered commands that are accessible by this shell will be greater than or equal to this number. The default is 128.
HOME: The default argument (home directory) for the cd command.
LINES: If this variable is set, the value is used to determine the column length for printing select lists. Select lists will print vertically until about two-thirds of LINES lines are filled.
MAIL: If this variable is set to the name of a mail file and the MAILPATH variable is not set, then the shell informs the user of arrival of mail in the specified file.
MAILCHECK: This variable specifies how often (in seconds) the shell will check for changes in the modification time of any of the files specified by the MAILPATH or MAIL variables. The default value is 600 seconds. When the time has elapsed the shell will check before issuing the next prompt.
MAILPATH: A colon (:) separated list of file names. If this variable is set then the shell informs the user of any modifications to the specified files that have occurred within the last MAILCHECK seconds. Each file name can be followed by a ``?'' and a message that will be printed. The message will undergo parameter substitution with the variable $_ defined as the name of the file that has changed. The default message is you have mail in $_.
PATH: The search path for commands (see ``Execution''). The user may not change PATH if executing under rksh (except in .profile).
PS1: The value of this variable is expanded for parameter substitution to define the primary prompt string which by default is ``$''. The character ``!'' in the primary prompt string is replaced by the command number (see ``Command re-entry'').
PS2: Secondary prompt string, by default ````>'' ''.
PS3: Selection prompt string used within a select loop, by default ``#?''.
PS4: The value of this variable is expanded for parameter substitution and precedes each line of an execution trace. If omitted, the execution trace prompt is ``+''.
SHELL: The pathname of the shell is kept in the environment. At invocation, if the basename of this variable matches the pattern *r*sh, then the shell becomes restricted.
TMOUT: If set to a value greater than zero, the shell will terminate if a command is not entered within the prescribed number of seconds after issuing the PS1 prompt. (Note that the shell can be compiled with a maximum bound for this value which cannot be exceeded.)
VISUAL: If the value of this variable ends in ``gmacs'', or ``vi'' then the corresponding option (see set in special ``Special commands'') will be turned on.

The shell gives default values to PATH, PS1, PS2, MAILCHECK, TMOUT and IFS. HOME, MAIL and SHELL are set by login(1).

Blank interpretation

After parameter and command substitution, the results of substitutions are scanned for the field separator characters (those found in IFS) and split into distinct arguments where such characters are found. Explicit null arguments (``""'' or ``'''') are retained. Implicit null arguments (those resulting from parameters that have no values) are removed.

Filename generation

Following substitution, each command word is scanned for the characters ``

'', ``?'', and ``['' unless the -f option has been set. If one of these characters appears then the word is regarded as a pattern. The word is replaced with lexicographically sorted file names that match the pattern. If no file name is found that matches the pattern, then the word is left unchanged. When a pattern is used for file name generation, the character ``.'' at the start of a file name or immediately following a ``/'', as well as the character ``/'' itself, must be matched explicitly. In other instances of pattern matching the ``/'' and ``.'' are not treated specially.

: Matches any string, including the null string.
?: Matches any single character.
[...]: Matches any one of the enclosed characters. A pair of characters separated by - matches any character lexically between the pair, inclusive. If the first character following the opening [ is a ! then any character not enclosed is matched. A - can be included in the character set by putting it as the first or last character.

A pattern-list is a list of one or more patterns separated from each other with a ``|''. Composite patterns can be formed with one or more of the following:

?(pattern-list): Optionally matches any one of the given patterns.
*(pattern-list): Matches zero or more occurrences of the given patterns.
+(pattern-list): Matches one or more occurrences of the given patterns.
@(pattern-list): Matches exactly one of the given patterns.
!(pattern-list): Matches anything, except one of the given patterns.

Quoting

Each of the metacharacters listed above (see ``Definitions'') has a special meaning to the shell and causes termination of a word unless quoted. A character may be quoted (that is, made to stand for itself) by preceding it with a ``\''. The pair ``\newline'' is removed. All characters enclosed between a pair of single quote marks (``''''), are quoted. A single quote cannot appear within single quotes. Inside double quote marks (``""''), parameter and command substitution occurs and ``\'' quotes the characters ``\'', ```'', ``"'', and ``$''. The meaning of ``$

'' and ``$@'' is identical when not quoted or when used as a variable assignment value or as a file name. However, when used as a command argument, "$" is equivalent to "$1d$2d...", where d is the first character of the IFS variable, whereas ``"$@"'' is equivalent to ``"$1"''d``"$2"''d``...'' Inside backquotes (````'') ``\'' quotes the characters ``\'', ```'', and ``$''. If the grave quotes occur within double quotes then ``\'' also quotes the character ``"''.

The special meaning of reserved words or aliases can be removed by quoting any character of the reserved word. The recognition of function names or special command names listed below cannot be altered by quoting them.

Arithmetic evaluation

An ability to perform integer arithmetic is provided with the special command let. Evaluations are performed using long arithmetic. Constants are of the form [base#]n where base is a decimal number between two and thirty-six representing the arithmetic base and n is a number in that base. If base# is omitted then base 10 is used.

An arithmetic expression uses the same syntax, precedence, and associativity of expression of the C language. All the integral operators, other than ++, --, ?:, and , are supported. Variables can be referenced by name within an arithmetic expression without using the parameter substitution syntax. When a variable is referenced, its value is evaluated as an arithmetic expression.

An internal integer representation of a variable can be specified with the -i option of the typeset special command. Arithmetic evaluation is performed on the value of each assignment to a variable with the -i attribute. If you do not specify an arithmetic base, the first assignment to the variable determines the arithmetic base. This base is used when parameter substitution occurs.

Since many of the arithmetic operators require quoting, an alternative form of the let command is provided. For any command which begins with a ``(('', all the characters until a matching ``))'' are treated as a quoted expression. More precisely, ((. . .)) is equivalent to let ``"''. . .``"''.

Prompting

When used interactively, the shell prompts with the parameter expanded value of PS1 before reading a command. If at any time a newline is typed and further input is needed to complete a command, then the secondary prompt (that is, the value of PS2) is issued.

Conditional expressions

A conditional expression is used with the [[ compound command to test attributes of files and to compare strings. Word splitting and file name generation are not performed on the words between [[ and ]]. Each expression can be constructed from one or more of the following unary or binary expressions:

-a file: True, if file exists.
-b file: True, if file exists and is a block special file.
-c file: True, if file exists and is a character special file.
-d file: True, if file exists and is a directory.
-f file: True, if file exists and is an ordinary file.
-g file: True, if file exists and is has its setgid bit set.
-k file: True, if file exists and is has its sticky bit set.
-n string: True, if length of string is non-zero.
-o option: True, if option named option is on.
-p file: True, if file exists and is a fifo special file or a pipe.
-r file: True, if file exists and is readable by current process.
-s file: True, if file exists and has size greater than zero.
-t fildes: True, if file descriptor number fildes is open and associated with a terminal device.
-u file: True, if file exists and is has its setuid bit set.
-w file: True, if file exists and is writable by current process.
-x file: True, if file exists and is executable by current process. If file exists and is a directory, then the current process has permission to search in the directory.
-z string: True, if length of string is zero.
-L file: True, if file exists and is a symbolic link.
-O file: True, if file exists and is owned by the effective user id of this process.
-G file: True, if file exists and its group matches the effective group id of this process.
-S file: True, if file exists and is a socket.
file1 -nt file2: True, if file1 exists and is newer than file2.
file1 -ot file2: True, if file1 exists and is older than file2.
file1 -ef file2: True, if file1 and file2 exist and refer to the same file.
string = pattern: True, if string matches pattern.
string != pattern: True, if string does not match pattern.
string1 < string2: True, if string1 comes before string2 based on ASCII value of their characters.
string1 > string2: True, if string1 comes after string2 based on ASCII value of their characters.
exp1 -eq exp2: True, if exp1 is equal to exp2.
exp1 -ne exp2: True, if exp1 is not equal to exp2.
exp1 -lt exp2: True, if exp1 is less than exp2.
exp1 -gt exp2: True, if exp1 is greater than exp2.
exp1 -le exp2: True, if exp1 is less than or equal to exp2.
exp1 -ge exp2: True, if exp1 is greater than or equal to exp2.

In each of the above expressions, if file is of the form /dev/fd/n, where n is an integer, then the test applied to the open file whose descriptor number is n.

A compound expression can be constructed from these primitives by using any of the following, listed in decreasing order of precedence.

(expression): True, if expression is true. Used to group expressions.
! expression: True, if expression is false.
expression1 && expression2: True, if expression1 and expression2 are both true.
expression1 || expression2: True, if either expression1 or expression2 is true.

Input/Output

Before a command is executed, its input and output may be redirected using a special notation interpreted by the shell. The following may appear anywhere in a simple-command or may precede or follow a command and are not passed on to the invoked command. Command and parameter substitution occur before word

or digit is used except as noted below. File name generation occurs only if the pattern matches a single file and blank interpretation is not performed.

<word: Use file word as standard input (file descriptor 0).
>word: Use file word as standard output (file descriptor 1). If the file does not exist then it is created. If the file exists, is a regular file, and the noclobber option is on, this causes an error; otherwise, it is truncated to zero length.
>|word: Same as >, except that it overrides the noclobber option.
>>word: Use file word as standard output. If the file exists then output is appended to it (by first seeking to the end-of-file); otherwise, the file is created.
<>word: Open file word for reading and writing as standard input.
<<[-]word: The shell input is read up to a line that is the same as word, or to an end-of-file. No parameter substitution, command substitution or file name generation is performed on word. The resulting document, called a ``here-document'', becomes the standard input. If any character of word is quoted, then no interpretation is placed upon the characters of the document; otherwise, parameter and command substitution occurs, ``\newline'' is ignored, and ``\'' must be used to quote the characters ``\'', ``$'', ```'', and the first character of word. If - is appended to <<, then all leading tabs are stripped from word and from the document.
<&digit: The standard input is duplicated from file descriptor digit (see dup(2)). Similarly for the standard output using >& digit.
``<&-'': The standard input is closed. Similarly for the standard output using ``>&-''.
<&p: The input from the co-process is moved to standard input.
>&p: The output to the co-process is moved to standard output.

If one of the above is preceded by a digit, then the file descriptor number referred to is that specified by the digit (instead of the default 0 or 1). For example:

... 2>&1

means file descriptor 2 is to be opened for writing as a duplicate of file descriptor 1.

The order in which redirections are specified is significant. The shell evaluates each redirection in terms of the (file descriptor, file) association at the time of evaluation. For example:

... 1>fname 2>&1

first associates file descriptor 1 with file fname. It then associates file descriptor 2 with the file associated with file descriptor 1 (that is, fname). If the order of redirections were reversed, file descriptor 2 would be associated with the terminal (assuming file descriptor 1 had been) and then file descriptor 1 would be associated with file fname.

If a command is followed by & and job control is not active, then the default standard input for the command is the empty file /dev/null. Otherwise, the environment for the execution of a command contains the file descriptors of the invoking shell as modified by input/output specifications.

Environment

The environment (see environ(5)) is a list of name-value pairs that is passed to an executed program in the same way as a normal argument list. The names must be identifiers and the values are character strings. The shell interacts with the environment in several ways. On invocation, the shell scans the environment and creates a variable for each name found, giving it the corresponding value and marking it export. Executed commands inherit the environment. If the user modifies the values of these variables or creates new ones, using the export or typeset -x commands they become part of the environment. The environment seen by any executed command is thus composed of any name-value pairs originally inherited by the shell, whose values may be modified by the current shell, plus any additions which must be noted in export or typeset -x commands.

The environment for any simple-command or function may be augmented by prefixing it with one or more variable assignments. A variable assignment argument is a word of the form identifier=value. Thus:

TERM=450 cmd args

and

(export TERM; TERM=450; cmd args)

are equivalent (as far as the above execution of cmd is concerned except for commands listed with one or two daggers, +, in the Special Commands section).

If the -k flag is set, all variable assignment arguments are placed in the environment, even if they occur after the command name. The following first prints a=b c and then c:

echo a=b c
set -k
echo a=b c

This feature is intended for use with scripts written for early versions of the shell and its use in new scripts is strongly discouraged. It is likely to disappear someday.

Functions

The function reserved word, described in ``Commands'' is used to define shell functions. Shell functions are read in and stored internally. Alias names are resolved when the function is read. Functions are executed like commands with the arguments passed as positional parameters (see ``Execution'').

Functions execute in the same process as the caller and share all files and present working directory with the caller. Traps caught by the caller are reset to their default action inside the function. A trap condition that is not caught or ignored by the function causes the function to terminate and the condition to be passed on to the caller. A trap on EXIT set inside a function is executed after the function completes in the environment of the caller. Ordinarily, variables are shared between the calling program and the function. However, the typeset special command used within a function defines local variables whose scope includes the current function and all functions it calls.

The special command return is used to return from function calls. Errors within functions return control to the caller.

Function identifiers can be listed with the -f or +f option of the typeset special command. The text of functions may also be listed with -f. Function can be undefined with the -f option of the unset special command.

Ordinarily, functions are unset when the shell executes a shell script. The -xf option of the typeset command allows a function to be exported to scripts that are executed without a separate invocation of the shell. Functions that need to be defined across separate invocations of the shell should be specified in the ENV file with the -xf option of typeset.

Jobs

If the monitor option of the set command is turned on, an interactive shell associates a job with each pipeline. It keeps a table of current jobs, printed by the jobs command, and assigns them small integer numbers. When a job is started asynchronously with &, the shell prints a line which looks like:

[1] 1234

indicating that the job which was started asynchronously was job number 1 and had one (top-level) process, whose process id was 1234.

If you are running a job and wish to do something else you may hit the key ^Z (<Ctrl>-z) which sends a STOP signal to the current job. The shell will then normally indicate that the job has been stopped, and print another prompt. You can then manipulate the state of this job, putting it in the background with the bg command, or run some other commands and then eventually bring the job back into the foreground with the foreground command fg. A ^Z takes effect immediately and is like an interrupt in that pending output and unread input are discarded when it is typed.

A job being run in the background will stop if it tries to read from the terminal. Background jobs are normally allowed to produce output, but this can be disabled by giving the command stty tostop. If you set this tty option, then background jobs will stop when they try to produce output like they do when they try to read input.

There are several ways to refer to jobs in the shell. A job can be referred to by the process id of any process of the job or by one of the following:

%number: The job with the given number.
%string: Any job whose command line begins with string.
%?string: Any job whose command line contains string.
%%: Current job.
%+: Equivalent to %%.
%-: Previous job.

This shell learns immediately whenever a process changes state. It normally informs you whenever a job becomes blocked so that no further progress is possible, but only just before it prints a prompt. This is done so that it does not otherwise disturb your work.

When the monitor mode is on, each background job that completes triggers any trap set for CHLD.

When you try to leave the shell while jobs are running or stopped, you will be warned that `You have stopped(running) jobs.' You may use the jobs command to see what they are. If you do this or immediately try to exit again, the shell will not warn you a second time, and the stopped jobs will be terminated.

Signals

When a command is run in the background (that is, when it is followed by &) and the job monitor option is active, the command does not receive INTERRUPT or QUIT signals. When a command is run in the background (that is, when it is followed by &) and the job monitor option is not active, the command receives INTERRUPT or QUIT signals but ignores them. Otherwise, signals have the values inherited by the shell from its parent (but see also the trap command below).

Execution

Each time a command is executed, the above substitutions are carried out. If the command name matches one of those listed in ``Special commands'' it is executed within the current shell process. Next, the command name is checked to see if it matches one of the user defined functions. If it does, the positional parameters are saved and then reset to the arguments of the function call. When the function completes or issues a return, the positional parameter list is restored and any trap set on EXIT within the function is executed. The value of a function is the value of the last command executed. A function is also executed in the current shell process. If a command name is not a special command or a user defined function, a process is created and an attempt is made to execute the command via exec(2).

The shell variable PATH defines the search path for the directory containing the command. Alternative directory names are separated by a colon (:). The default path is /usr/bin: (specifying /usr/bin and the current directory in that order). The current directory can be specified by two or more adjacent colons, or by a colon at the beginning or end of the path list. If the command name contains a ``/'' then the search path is not used. Otherwise, each directory in the path is searched for an executable file. If the file has execute permission but is not a directory or an a.out file, it is assumed to be a file containing shell commands. A sub-shell is spawned to read it. All non-exported aliases, functions, and variables, are removed in this case. A parenthesized command is executed in a sub-shell without removing non-exported quantities.

Command re-entry

The text of the last HISTSIZE (default 128) commands entered from a terminal device is saved in a history file. The file $HOME/.sh_history is used if the file denoted by the HISTFILE variable is not set or is not writable. A shell can access the commands of all interactive shells which use the same named HISTFILE. The special command fc is used to list or edit a portion of this file. The portion of the file to be edited or listed can be selected by number or by giving the first character or characters of the command. A single command or range of commands can be specified. If you do not specify an editor program as an argument to fc then the value of the variable FCEDIT is used. If FCEDIT is not defined then /usr/bin/ed is used. The edited command(s) is printed and re-executed upon leaving the editor. The editor name - is used to skip the editing phase and to re-execute the command. In this case a substitution variable of the form old=new can be used to modify the command before execution. For example, if r is aliased to 'fc -e -' then typing `r bad=good c' will re-execute the most recent command which starts with the letter ``c'', replacing the first occurrence of the string ``bad'' with the string ``good''.

In-line editing options

Normally, each command line entered from a terminal device is simply typed followed by a newline (<Return> or <LINE FEED>). If the gmacs, or vi option is active, the user can edit the command line. To be in any of these edit modes set the corresponding option. An editing option is automatically selected each time the VISUAL or EDITOR variable is assigned a value ending in any of these option names.

The editing features require that the user's terminal accept <Return> as carriage return without line feed and that a space (`') must overwrite the current character on the screen.

The editing modes implement a concept where the user is looking through a window at the current line. The window width is the value of COLUMNS if it is defined, otherwise 80. If the line is longer than the window width minus two, a mark is displayed at the end of the window to notify the user. As the cursor moves and reaches the window boundaries the window will be centered about the cursor. The mark is a ``>'' (<``,'' ``*'') if the line extends on the right (left, both) side(s) of the window.

The search commands in each edit mode provide access to the history file. Only strings are matched, not patterns, although a leading ``^'' in the string restricts the match to begin at the first character in the line.

vi editing mode

There are two typing modes. Initially, when you enter a command you are in the input mode. To edit, the user enters control mode by typing ESC (``\033'') and moves the cursor to the point needing correction and then inserts or deletes characters or words as needed. Most control commands accept an optional repeat count prior to the command.

When in vi mode on most systems, canonical processing is initially enabled and the command will be echoed again if the speed is 1200 baud or greater and it contains any control characters or less than one second has elapsed since the prompt was printed. The ESC character terminates canonical processing for the remainder of the command and the user can then modify the command line. This scheme has the advantages of canonical processing with the type-ahead echoing of raw mode.

If the option viraw is also set, the terminal will always have canonical processing disabled.

input edit commands

By default the editor is in input mode.

erase: (User defined erase character as defined by the stty command, usually ^H or #.) Delete previous character.
^W: Delete the previous blank separated word.
^D: Terminate the shell.
^V: Escape next character. Editing characters, the user's erase or kill characters may be entered in a command line or in a search string if preceded by a ^V. The ^V removes the next character's editing features (if any).
\: Escape the next erase or kill character.

motion edit commands

These commands will move the cursor.

[count]l: Cursor forward (right) one character.
[count]w: Cursor forward one alpha-numeric word.
[count]W: Cursor to the beginning of the next word that follows a blank.
[count]e: Cursor to end of word.
[count]E: Cursor to end of the current blank delimited word.
[count]h: Cursor backward (left) one character.
[count]b: Cursor backward one word.
[count]B: Cursor to preceding blank separated word.
[count]|: Cursor to column count.
[count]fc: Find the next character c in the current line.
[count]Fc: Find the previous character c in the current line.
[count]tc: Equivalent to f followed by h.
[count]Tc: Equivalent to F followed by l.
[count];: Repeats count times, the last single character find command, f, F, t, or T.
[count],: Reverses the last single character find command count times.
0: Cursor to start of line.
^: Cursor to first non-blank character in line.
$: Cursor to end of line.

search edit commands

These commands access your command history.

[count]k: Fetch previous command. Each time k is entered the previous command back in time is accessed.
[count]-: Equivalent to k.
[count]j: Fetch next command. Each time j is entered the next command forward in time is accessed.
[count]+: Equivalent to j.
[count]G: The command number count is fetched. The default is the least recent history command.
/string: Search backward through history for a previous command containing string. String is terminated by a <Return> or <NEW LINE>. If string is preceded by a ``^'', the matched line must begin with string. If string is null the previous string will be used.
?string: Same as / except that search will be in the forward direction.
n: Search for next match of the last pattern to / or ? commands.
N: Search for next match of the last pattern to / or ?, but in reverse direction. Search history for the string entered by the previous / command.

text modification edit commands

These commands will modify the line.

a: Enter input mode and enter text after the current character.
A: Append text to the end of the line. Equivalent to $a.
[count]cmotion
c[count]motion: Delete current character through the character that motion would move the cursor to and enter input mode. If motion is c, the entire line will be deleted and input mode entered.
C: Delete the current character through the end of line and enter input mode. Equivalent to c$.
S: Equivalent to cc.
D: Delete the current character through the end of line. Equivalent to d$.
[count]dmotion
d[count]motion: Delete current character through the character that motion would move to. If motion is d, the entire line will be deleted.
i: Enter input mode and insert text before the current character.
I: Insert text before the beginning of the line. Equivalent to 0i.
[count]P: Place the previous text modification before the cursor.
[count]p: Place the previous text modification after the cursor.
R: Enter input mode and replace characters on the screen with characters you type overlay fashion.
[count]rc: Replace the count character(s) starting at the current cursor position with c, and advance the cursor.
[count]x: Delete current character.
[count]X: Delete preceding character.
[count].: Repeat the previous text modification command.
[count]~: Invert the case of the count character(s) starting at the current cursor position and advance the cursor.
[count]_: Causes the count word of the previous command to be appended and input mode entered. The last word is used if count is omitted.
*: Causes an * to be appended to the current word and file name generation attempted. If no match is found, it rings the bell. Otherwise, the word is replaced by the matching pattern and input mode is entered.
\: Filename completion. Replaces the current word with the longest common prefix of all filenames matching the current word with an asterisk appended. If the match is unique, a ``/'' is appended if the file is a directory and a space is appended if the file is not a directory.

other edit commands

Miscellaneous commands.

[count]ymotion
y[count]motion: Yank current character through character that motion would move the cursor to and puts them into the delete buffer. The text and cursor are unchanged.
Y: Yanks from current position to end of line. Equivalent to y$.
u: Undo the last text modifying command.
U: Undo all the text modifying commands performed on the line.
[count]v: Returns the command fc -e ${VISUAL:-${EDITOR:-vi}} count in the input buffer. If count is omitted, then the current line is used.
^L: Line feed and print current line. Has effect only in control mode.
^J: (New line) Execute the current line, regardless of mode.
^M: (Return) Execute the current line, regardless of mode.
#: Sends the line after inserting a # in front of the line. Useful for causing the current line to be inserted in the history without being executed.
=: List the file names that match the current word if an asterisk were appended it.
@letter: Your alias list is searched for an alias by the name _letter and if an alias of this name is defined, its value will be inserted on the input queue for processing.

Emacs editing mode

This mode is entered by enabling either the emacs or gmacs option. The only difference between these two modes is the way they handle ^T. To edit, the user moves the cursor to the point needing correction and then inserts or deletes characters or words as needed. All the editing commands are control characters or escape sequences. The notation for control characters is caret (^) followed by the character. For example, ^F is the notation for <Ctrl>-f. This is entered by depressing <f> while holding down the <Ctrl> (control) key. (The notation ^? indicates the <Del> (delete) key.)

The notation for escape sequences is M- followed by a character. For example, M-f (pronounced Meta f) is entered by depressing ESC (ascii ``\033'') followed by <f>. (M-F would be the notation for ESC followed by SHIFT (capital) <F>.)

All edit commands operate from any place on the line (not just at the beginning). Neither the <Return> nor the <LINE FEED> key is entered after edit commands except when noted.

^F: Move cursor forward (right) one character.
M-f: Move cursor forward one word. (The emacs editor's idea of a word is a string of characters consisting of only letters, digits and underscores.)
^B: Move cursor backward (left) one character.
M-b: Move cursor backward one word.
^A: Move cursor to start of line.
^E: Move cursor to end of line.
^]char: Move cursor forward to character char on current line.
M-^]char: Move cursor back to character char on current line.
^X^X: Interchange the cursor and mark.
erase: (User defined erase character as defined by the stty(1) command, usually ^H or #.) Delete previous character.
^D: Delete current character.
M-d: Delete current word.
M-^H: (Meta-backspace) Delete previous word.
M-h: Delete previous word.
M-^?: (Meta-<Del>) Delete previous word (if your interrupt character is ^? (<Del>, the default) then this command will not work).
^T: Transpose current character with previous character in emacs mode. Transpose two previous characters in gmacs mode.
^C: Capitalize current character.
M-c: Capitalize current word.
M-l: Change the current word to lower case.
^K: Delete from the cursor to the end of the line. If preceded by a numerical parameter whose value is less than the current cursor position, then delete from given position up to the cursor. If preceded by a numerical parameter whose value is greater than the current cursor position, then delete from cursor up to given cursor position.
^W: Kill from the cursor to the mark.
M-p: Push the region from the cursor to the mark on the stack. (User defined kill character as defined by the stty command, usually ^U or @.) Kill the entire current line. If two kill characters are entered in succession, all kill characters from then on cause a line feed (useful when using paper terminals).
^Y: Restore last item removed from line. (Yank item back to the line.)
^L: Line feed and print current line.
^@: (Null character) Set mark.
M-space: (Meta space) Set mark.
^J: (New line) Execute the current line.
^M: (Return) Execute the current line.
eof: End-of-file character, normally ^D, is processed as an End-of-file only if the current line is null.
^P: Fetch previous command. Each time ^P is entered the previous command back in time is accessed. Moves back one line when not on the first line of a multi-line command.
M-<: Fetch the least recent (oldest) history line.
M->: Fetch the most recent (youngest) history line.
^N: Fetch next command line. Each time ^N is entered the next command line forward in time is accessed.
^Rstring: Reverse search history for a previous command line containing string. If a parameter of zero is given, the search is forward. String is terminated by a <Return> or <NEW LINE>. If string is preceded by a ^, the matched line must begin with string. If string is omitted, then the next command line containing the most recent string is accessed. In this case a parameter of zero reverses the direction of the search.
^O: Operate - Execute the current line and fetch the next line relative to current line from the history file.
M-digits: (Escape) Define numeric parameter, the digits are taken as a parameter to the next command. The commands that accept a parameter are ^F, ^B, erase, ^C, ^D, ^K, ^R, ^P, ^N, ^], M-., M-^], M-_, M-b, M-c, M-d, M-f, M-h M-l and M-^H.
M-letter: Soft-key - Your alias list is searched for an alias by the name _letter and if an alias of this name is defined, its value will be inserted on the input queue. The letter must not be one of the above meta-functions.
M-[letter: Soft-key - Your alias list is searched for an alias by the name __letter and if an alias of this name is defined, its value will be inserted on the input queue. The can be used to program functions keys on many terminals.
M-.: The last word of the previous command is inserted on the line. If preceded by a numeric parameter, the value of this parameter determines which word to insert rather than the last word.
M-_: Same as M-..
M-*: Attempt file name generation on the current word. An asterisk is appended if the word doesn't match any file or contain any special pattern characters.
M-ESC: File name completion. Replaces the current word with the longest common prefix of all filenames matching the current word with an asterisk appended. If the match is unique, a ``/'' is appended if the file is a directory and a space is appended if the file is not a directory.
M-=: List files matching current word pattern if an asterisk were appended.
^U: Multiply parameter of next command by 4.
\: Escape next character. Editing characters, the user's erase, kill and interrupt (normally ``^?'') characters may be entered in a command line or in a search string if preceded by a ``\''. The ``\'' removes the next character's editing features (if any).
^V: Display version of the shell.
M-#: Insert a ``#'' at the beginning of the line and execute it. This causes a comment to be inserted in the history file.

Special commands

The following simple-commands are executed in the shell process. Input/Output redirection is permitted. Unless otherwise indicated, the output is written on file descriptor 1 and the exit status, when there is no syntax error, is zero. Commands that are preceded by one or two + are treated specially in the following ways:

Variable assignment lists preceding the command remain in effect when the command completes.
I/O redirections are processed after variable assignments.
Errors cause a script that contains them to abort.
Words, following a command preceded by ++ that are in the format of a variable assignment, are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed.
The command only expands parameters.
Read the complete file then execute the commands. The commands are executed in the current shell environment. The search path specified by PATH is used to find the directory containing file. If any arguments arg are given, they become the positional parameters. Otherwise the positional parameters are unchanged. The exit status is the exit status of the last command executed.
alias with no arguments prints the list of aliases in the form name=value on standard output. An alias is defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution. The -t flag is used to set and list tracked aliases. The value of a tracked alias is the full pathname corresponding to the given name. The value becomes undefined when the value of PATH is reset but the aliases remain tracked. Without the -t flag, for each name in the argument list for which no value is given, the name and value of the alias is printed. The -x flag is used to set or print exported aliases. An exported alias is defined for scripts invoked by name. The exit status is non-zero if a name is given, but no value, for which no alias has been defined.
This command is only on systems that support job control. Puts each specified job into the background. The current job is put in the background if job is not specified. See ``Jobs'' for a description of the format of job.
Exit from the enclosing for, while, until or select loop, if any. If n is specified then break n levels.
Resume the next iteration of the enclosing for, while, until or select loop. If n is specified then resume at the n-th enclosing loop.
This command can be in either of two forms. In the first form it changes the current directory to arg. If arg is - the directory is changed to the previous directory. The shell variable HOME is the default arg. The variable PWD is set to the current directory. The shell variable CDPATH defines the search path for the directory containing arg. Alternative directory names are separated by a colon (:). The default path is <null> (specifying the current directory). Note that the current directory is specified by a null path name, which can appear immediately after the equal sign or between the colon delimiters anywhere else in the path list. If arg begins with a / then the search path is not used. Otherwise, each directory in the path is searched for arg.
The second form of cd substitutes the string new for the string old in the current directory name, PWD and tries to change to this new directory.
The cd command may not be executed by rksh.
See echo(1) for usage and description.
The arguments are read as input to the shell and the resulting command(s) executed.
If arg is given, the command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments may appear and affect the current process. If no arguments are given the effect of this command is to modify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are opened with this mechanism are closed when invoking another program.
Causes the shell to exit with the exit status specified by n. If n is omitted then the exit status is that of the last command executed. An end-of-file will also cause the shell to exit except for a shell which has the ignoreeof option (see set below) turned on.
The given names are marked for automatic export to the environment of subsequently-executed commands.
In the first form, a range of commands from first to last is selected from the last HISTSIZE commands that were typed at the terminal. The arguments first and last may be specified as a number or as a string. A string is used to locate the most recent command starting with the given string. A negative number is used as an offset to the current command number. If the flag -l, is selected, the commands are listed on standard output. Otherwise, the editor program ename is invoked on a file containing these keyboard commands. If ename is not supplied, then the value of the variable FCEDIT (default /usr/bin/ed) is used as the editor. When editing is complete, the edited command(s) is executed. If last is not specified then it will be set to first. If first is not specified the default is the previous command for editing and -16 for listing. The flag -r reverses the order of the commands and the flag -n suppresses command numbers when listing. In the second form the command is re-executed after the substitution old=new is performed.
This command is only on systems that support job control. Each job specified is brought to the foreground. Otherwise, the current job is brought into the foreground. See Jobs for a description of the format of job.
Checks arg for legal options. If arg is omitted, the positional parameters are used. An option argument begins with a + or a -. An option not beginning with + or - or the argument -- ends the options. optstring contains the letters that getopts recognizes. If a letter is followed by a :, that option is expected to have an argument. The options can be separated from the argument by blanks.
getopts places the next option letter it finds inside variable name each time it is invoked with a + prepended when arg begins with a +. The index of the next arg is stored in OPTIND. The option argument, if any, gets stored in OPTARG.
A leading : in optstring causes getopts to store the letter of an invalid option in OPTARG, and to set name to ``?'' for an unknown option and to ``:'' when a required option is missing. Otherwise, getopts prints an error message. The exit status is non-zero when there are no more options.
Lists information about each given job; or all active jobs if job is omitted. The -l flag lists process ids in addition to the normal information. The -n flag only displays jobs that have stopped or exited since last notified. The -p flag causes only the process group to be listed. See ``Jobs'' for a description of the format of job.
Sends either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are either given by number or by names (as given in /usr/include/signal.h, stripped of the prefix SIG). If the signal being sent is TERM (terminate) or HUP (hangup), then the job or process will be sent a CONT (continue) signal if it is stopped. The argument job can the process id of a process that is not a member of one of the active jobs. See ``Jobs'' for a description of the format of job. In the second form, kill -l, the signal numbers and names are listed.
Each arg is a separate ``arithmetic expression'' to be evaluated. See ``Arithmetic evaluation'' for a description of arithmetic expression evaluation.
The exit status is 0 if the value of the last expression is non-zero, and 1 otherwise.
Equivalent to exec /usr/bin/newgrp arg . . .
The shell output mechanism. With no flags or with flag - or -- the arguments are printed on standard output as described by echo(1). In raw mode, -R or -r, the escape conventions of echo are ignored. The -R option will print all subsequent arguments and options other than -n. The -p option causes the arguments to be written onto the pipe of the process spawned with |& instead of standard output. The -s option causes the arguments to be written onto the history file instead of standard output. The -u flag can be used to specify a one digit file descriptor unit number n on which the output will be placed. The default is 1. If the flag -n is used, no newline is added to the output.
Equivalent to print -r - $PWD
The shell input mechanism. One line is read and is broken up into fields using the characters in IFS as separators. In raw mode, -r, a ``\'' at the end of a line does not signify line continuation. The first field is assigned to the first name, the second field to the second name, and so on, with leftover fields assigned to the last name. The -p option causes the input line to be taken from the input pipe of a process spawned by the shell using |&. If the -s flag is present, the input will be saved as a command in the history file. The flag -u can be used to specify a one digit file descriptor unit to read from. The file descriptor can be opened with the exec special command. The default value of n is 0. If name is omitted then REPLY is used as the default name. The exit status is 0 unless an end-of-file is encountered. An end-of-file with the -p option causes cleanup for this process so that another can be spawned. If the first argument contains a ``?'', the remainder of this word is used as a prompt on standard error when the shell is interactive. The exit status is 0 unless an end-of-file is encountered.
The given names are marked readonly and these names cannot be changed by subsequent assignment.
Causes a shell function to return to the invoking script with the return status specified by n. If n is omitted then the return status is that of the last command executed. If return is invoked while not in a function or a . script, then it is the same as an exit.
The flags for this command have meaning as follows:

-A
Array assignment. Unset the variable name and assign values sequentially from the list arg. If +A is used, the variable name is not unset first.

-a
All subsequent variables that are defined are automatically exported.

-e
If a command has a non-zero exit status, execute the ERR trap, if set, and exit. This mode is disabled while reading profiles.

-f
Disables file name generation.

-h
Each command becomes a tracked alias when first encountered.

-k
All variable assignment arguments are placed in the environment for a command, not just those that precede the command name.

-m
Background jobs will run in a separate process group and a line will print upon completion. The exit status of background jobs is reported in a completion message. On systems with job control, this flag is turned on automatically for interactive shells.

-n
Read commands and check them for syntax errors, but do not execute them. Ignored for interactive shells.

-o
The following argument can be one of the following option names:

allexport
Same as -a.

errexit
Same as -e.

bgnice
All background jobs are run at a lower priority. This is the default mode.

emacs
Puts you in an emacs style in-line editor for command entry.

gmacs
Puts you in a gmacs style in-line editor for command entry.

ignoreeof
The shell will not exit on end-of-file. The command exit must be used.

keyword
Same as -k.

markdirs
All directory names resulting from file name generation have a trailing ``/'' appended.

monitor
Same as -m.

noclobber
Prevents redirection > from truncating existing files. Require >| to truncate a file when turned on.

noexec
Same as -n.

noglob
Same as -f.

nolog
Do not save function definitions in history file.

nounset
Same as -u.

privileged
Same as -p.

verbose
Same as -v.

trackall
Same as -h.

vi
Puts you in insert mode of a vi style in-line editor until you hit escape character ``033''. This puts you in move mode. A return sends the line.

viraw
Each character is processed as it is typed in vi mode.

xtrace
Same as -x.
If no option name is supplied then the current option settings are printed.

-p
Disables processing of the $HOME/.profile file and uses the file /etc/suid_profile instead of the ENV file. This mode is on whenever the effective uid (gid) is not equal to the real uid (gid). When the -p flag is not present, the shell will set the effective uid and gid to the real uid and gid if they don't match and if the effective uid is <100. When the effective uid is >=100, the effective gid is not set to the real gid. When the effective uid is <100 and is set to the real uid and ksh88 is invoked without -p flag, set -p and set +p have no effect.

-s
Sort the positional parameters lexicographically.

-t
Exit after reading and executing one command.

-u
Treat unset parameters as an error when substituting.

-v
Print shell input lines as they are read.

-x
Print commands and their arguments as they are executed.

-
Turns off -x and -v flags and stops examining arguments for flags.

--
Do not change any of the flags; useful in setting $1 to a value beginning with -. If no arguments follow this flag then the positional parameters are unset.
Using + rather than - causes these flags to be turned off. These flags can also be used upon invocation of the shell. The current set of flags may be found in $-. Unless -A is specified, the remaining arguments are positional parameters and are assigned, in order, to $1 $2 .... If no arguments are given then the names and values of all variables are printed on the standard output.
The positional parameters from $n+1 ... are renamed $1 ... , default n is 1. The parameter n can be any arithmetic expression that evaluates to a non-negative number less than or equal to $#.
Print the accumulated user and system times for the shell and for processes run from the shell.
arg is a command to be read and executed when the shell receives signal(s) sig. (Note that arg is scanned once when the trap is set and once when the trap is taken.) Each sig can be given as a number or as the name of the signal. Trap commands are executed in order of signal number. Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective. If arg is omitted or is -, then all trap(s) sig are reset to their original values. If arg is the null string then this signal is ignored by the shell and by the commands it invokes. If sig is ERR then arg will be executed whenever a command has a non-zero exit status. sig is DEBUG then arg will be executed after each command. If sig is 0 or EXIT and the trap statement is executed inside the body of a function, then the command arg is executed after the function completes. If sig is 0 or EXIT for a trap set outside any function then the command arg is executed on exit from the shell. The trap command with no arguments prints a list of commands associated with each signal number.
Sets attributes and values for shell variables. When invoked inside a function, a new instance of the variable name is created. The parameter value and type are restored when the function completes. The following list of attributes may be specified:

-H
This flag provides UNIX to host-name file mapping on non-UNIX machines.

-L
Left justify and remove leading blanks from value. If n is non-zero it defines the width of the field, otherwise it is determined by the width of the value of first assignment. When the variable is assigned to, it is filled on the right with blanks or truncated, if necessary, to fit into the field. Leading zeros are removed if the -Z flag is also set. The -R flag is turned off.

-R
Right justify and fill with leading blanks. If n is non-zero it defines the width of the field, otherwise it is determined by the width of the value of first assignment. The field is left filled with blanks or truncated from the end if the variable is reassigned. The L flag is turned off.

-Z
Right justify and fill with leading zeros if the first non-blank character is a digit and the -L flag has not been set. If n is non-zero it defines the width of the field, otherwise it is determined by the width of the value of first assignment.

-f
The names refer to function names rather than variable names. No assignments can be made and the only other valid flags are -t, -u and -x. The flag -t turns on execution tracing for this function. The flag -u causes this function to be marked undefined. The FPATH variable will be searched to find the function definition when the function is referenced. The flag -x allows the function definition to remain in effect across shell procedures invoked by name.

-i
Variable is an integer. This makes arithmetic faster. If n is non-zero it defines the output arithmetic base, otherwise the first assignment determines the output base.

-l
All upper-case characters converted to lower-case. The upper-case flag, -u is turned off.

-r
The given names are marked readonly and these names cannot be changed by subsequent assignment.

-t
Tags the variables. Tags are user definable and have no special meaning to the shell.

-u
All lower-case characters are converted to upper-case characters. The lower-case flag, -l is turned off.

-x
The given names are marked for automatic export to the environment of subsequently-executed commands.
Using + rather than - causes these flags to be turned off. If no name arguments are given but flags are specified, a list of names (and optionally the values) of the variables which have these flags set is printed. (Using + rather than - keeps the values from being printed.) If no names and flags are given, the names and attributes of all variables are printed.
ulimit prints or sets hard or soft resource limits. These limits are described in getrlimit(2).
If limit is not present, ulimit prints the specified limits. Any number of limits may be printed at one time. The -a option prints all limits.
If limit is present, ulimit sets the specified limit to limit. The string unlimited requests the largest valid limit. Limits may be set for only one resource at a time. Any user may set a soft limit to any value below the hard limit. Any user may lower a hard limit. Only a privileged user may raise a hard limit; see su(1M).
The -H option specifies a hard limit. The -S option specifies a soft limit. If neither option is specified, ulimit will set both limits and print the soft limit.
The following options specify the resource whose limits are to be printed or set. If no option is specified, the file size limit is printed or set.

-c
maximum core file size (in 512-byte blocks)

-d
maximum size of data segment or heap (in kbytes)

-f
maximum file size (in 512-byte blocks)

-n
maximum file descriptor plus 1

-s
maximum size of stack segment (in kbytes)

-t
maximum CPU time (in seconds)

-v
maximum size of virtual memory (in kbytes)

If no option is given, -f is assumed.
The user file-creation mask is set to mask (see umask(2)). mask can either be an octal number or a symbolic value as described in chmod(1). If a symbolic value is given, the new umask value is the complement of the result of applying mask to the complement of the previous umask value. If mask is omitted, the current value of the mask is printed.
The variables given by the list of names are removed from the alias list.
The variables given by the list of names are unassigned, that is, their values and attributes are erased. Read-only variables cannot be unset. If the flag, -f, is set, then the names refer to function names. Unsetting ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT, and _ removes their special meaning even if they are subsequently assigned to.
Wait for the specified job and report its termination status. If job is not given then all currently active child processes are waited for. The exit status from this command is that of the process waited for. See ``Jobs'' for a description of the format of job.
For each name, indicate how it would be interpreted if used as a command name.

-v
produces a more verbose report.

-p
does a path search for name even if name is an alias, a function, or a reserved word.

Invocation

If the shell is invoked by exec(2), and the first character of argument zero ($0) is -, then the shell is assumed to be a login shell and commands are read from /etc/profile and then from either .profile in the current directory or $HOME/.profile, if either file exists. Next, commands are read from the file named by performing parameter substitution on the value of the environment variable ENV if the file exists. If the -s flag is not present and arg is, then a path search is performed on the first arg to determine the name of the script to execute. The script arg must have read permission and any setuid and setgid settings will be ignored. Commands are then read as described below; the following flags are interpreted by the shell when it is invoked:

-c string: If the -c flag is present then commands are read from string.
-s: If the -s flag is present or if no arguments remain then commands are read from the standard input. Shell output, except for the output of the Special commands listed above, is written to file descriptor 2.
-i: If the -i flag is present or if the shell input and output are attached to a terminal (as told by ioctl(2)) then this shell is interactive. In this case TERM is ignored (so that kill 0 does not kill an interactive shell) and INTR is caught and ignored (so that wait is interruptible). In all cases, QUIT is ignored by the shell.
-r: If the -r flag is present the shell is a restricted shell.

The remaining flags and arguments are described under the set command above.

rksh only

rksh is used to set up login names and execution environments whose capabilities are more controlled than those of the standard shell. The actions of rksh are identical to those of sh, except that the following are disallowed:

changing directory (see cd(1))
setting the value of SHELL, ENV, or PATH
specifying path or command names containing ``/''
redirecting output (>, >|, <>, and >>).

The restrictions above are enforced after .profile and the ENV files are interpreted.

When a command to be executed is found to be a shell procedure, rksh invokes ksh88 to execute it. Thus, it is possible to provide to the end-user shell procedures that have access to the full power of the standard shell, while imposing a limited menu of commands; this scheme assumes that the end-user does not have write and execute permissions in the same directory.

The net effect of these rules is that the writer of the .profile has complete control over user actions, by performing guaranteed setup actions and leaving the user in an appropriate directory (probably not the login directory).

The system administrator often sets up a directory of commands (that is, /usr/rbin) that can be safely invoked by rksh.

Files

/etc/passwd
/etc/profile
/etc/suid_profile
$HOME/.profile
/tmp/sh
/dev/null
/usr/lib/locale/locale/LC_MESSAGES/uxue: language-specific message file (See LANG on environ(5).)

Exit codes

Errors detected by the shell, such as syntax errors, cause the shell to return a non-zero exit status. Otherwise, the shell returns the exit status of the last command executed (see also the exit command above). If the shell is being used non-interactively then execution of the shell file is abandoned. Run time errors detected by the shell are reported by printing the command or function name and the error condition. If the line number that the error occurred on is greater than one, then the line number is also printed in square brackets ([]) after the command or function name.

References

a.out(4), cat(1), cd(1), chmod(1), cut(1), dup(2), echo(1), env(1), environ(5), exec(2), fork(2), ioctl(2), lseek(2), newgrp(1M), paste(1), pipe(2), profile(4), rand(3C), signal(2), stty(1), test(1), ulimit(2), umask(1), umask(2), vi(1), wait(2)

Morris I. Bolsky and David G. Korn, The KornShell Command and Programming Language, Prentice Hall, 1989

Notices

If a command which is a tracked alias is executed, and then a command with the same name is installed in a directory in the search path before the directory where the original command was found, the shell will continue to exec the original command. Use the -t option of the alias command to correct this situation.

Some very old shell scripts contain a ``^'' as a synonym for the pipe character ``|''.

Using the fc built-in command within a compound command will cause the whole command to disappear from the history file.

The built-in command . file reads the whole file before any commands are executed. Therefore, alias and unalias commands in the file will not apply to any functions defined in the file.

Traps are not processed while a job is waiting for a foreground process. Thus, a trap on CHLD won't be executed until the foreground job terminates.