Term::Shell(3) User Contributed Perl Documentation Term::Shell(3)NAMETerm::Shell - A simple command-line shell framework.
SYNOPSIS
package MyShell;
use base qw(Term::Shell);
sub run_command1 { print "command 1!\n"; }
sub smry_command1 { "what does command1 do?" }
sub help_command1 {
<<'END';
Help on 'command1', whatever that may be...
END
}
sub run_command2 { print "command 2!\n"; }
package main;
my $shell = MyShell->new;
$shell->cmdloop;
DESCRIPTIONTerm::Shell lets you write simple command-line shells. All the boring
details like command-line parsing, terminal handling, and tab
completion are handled for you.
The base class comes with two commands pre-defined: exit and help.
To write a shell with an "exec" command, do something like this:
package MyShell;
use base qw(Term::Shell); # or manually edit @MyShell::ISA.
sub run_exec {
my ($o, $cmd, @args) = @_;
if ($cmd ne $0) {
print "I'm sorry you're leaving us...\n";
}
exec $cmd, @args;
exit 1;
}
When Term::Shell needs to handle the "exec" command, it will invoke
this method. That's all there is to it! You write handlers, and
Term::Shell handles the gory details.
Using Term::Shell Shells
How do you bring your shell to life? Assuming the package "MyShell"
contains your actions, just do this:
use MyShell;
my $shell = MyShell->new;
# Setup code here (if you wish)
# Invoke the shell
$shell->cmdloop;
# Cleanup code here (if you wish)
Most people put the setup code in the shell itself, so you can usually
get away with this:
use MyShell;
MyShell->new->cmdloop;
It's that simple! All the actions and command handlers go in
"MyShell.pm", and your main program is simple. In fact, it's so simple
that some people like to write both the actions and the invocation in
the same file:
package main;
MyShell->new->cmdloop;
package MyShell;
use base qw(Term::Shell);
# Actions here
Adding commands to your shell is just as easy, if not easier.
Adding Commands to Your Shell
For every command "foo", Term::Shell needs a method called "run_foo()",
where 'foo' is what the user will type in. The method will be called
with the Term::Shell object as the first parameter, followed by any
arguments the user typed after the command.
Several prefixes other than "run_" are supported; each prefix tells
Term::Shell to call that handler under different circumstances. The
following list enumerates all the "special" prefixes. Term::Shell will
ignore any method that doesn't start with a prefix listed here.
1. run_foo()
Adds the command "foo" to the list of supported commands. The
method's return value is saved by Term::Shell, but is not used.
The method is called with the Term::Shell object as its first
argument, followed by any arguments the user typed in.
Special case: if you provide a method "run_()", Term::Shell will
call it whenever the user enters a blank line. A blank line is
anything which matches the regular expression "/^\s*$/".
2. help_foo()
Adds the command "foo" to the list of help topics. This means the
user may enter 'help foo' and get a help screen. It should return a
single string to be displayed to the user.
The method is called with the Term::Shell object as its first
argument, followed by any arguments the user typed in after 'help
foo'. You can implement hierarchical help documents by using the
arguments.
If you do not provide a "help_foo()" method, typing 'help foo'
produces an error message.
3. smry_foo()
Should return a one-line summary of "foo", to be displayed in the
help screen.
This method is called with the Term::Shell object as its first
argument, and no other arguments.
If you do not provide a "smry_foo()" method, then the string
'undocumented' is used instead.
4. comp_foo()
Provides custom tab-completion for "foo". That means if the user
types 'foo ' and then hits <TAB>, this method will be called. It
should return an array reference containing a list of possible
completions.
This method is called with the Term::Shell object as its first
argument, followed by the three arguments:
1. $word
The word the user is trying to complete.
2. $line
The line as typed by the user so far.
3. $start
The offset into $line where $word starts.
If you do not provide "comp_foo()", Term::Shell will always return
no completions for "foo".
Special case: if you provide "comp_()", Term::Shell will call it
when the user is trying to complete the name of a command.
Term::Shell provides a default "comp_()" method, which completes
the actions that you have written handlers for. If you want to
provide tab-completion for commands that do not have handlers,
override "comp_()".
5. alias_foo()
Returns a list of aliases for "foo". When one of the aliases is
used instead of "foo", the corresponding handler for "foo" is
called.
6. catch_run()catch_help()catch_comp()catch_smry()
Called when an undefined action is entered by the user. Normally
when the user enters an unrecognized command, Term::Shell will
print an error message and continue.
This method is called with the Term::Shell object, the command
typed by the user, and then the arguments which would normally be
passed to the real handler.
The "catch_" methods may do anything the original function would
have done. If you want, you can implement all the commands in it,
but that means you're doing more work than you have to. Be lazy.
When you want something done right...
You sometimes have to do it yourself. Introducing add_handlers().
Naturally, it adds a handler to the list of defined handlers in the
shell.
Term::Shell can't always find the commands you want to implement by
searching the inheritance tree. Having an AUTOLOAD() method, for
instance, will break this system. In that situation, you may wish to
tell Term::Shell about the extra commands available using
add_handlers():
package MyShell;
use base qw(Term::Shell);
sub AUTOLOAD {
if ($AUTOLOAD =~ /::run_fuzz$/) {
# code for 'fuzz' command
}
elsif ($AUTOLOAD =~ /::run_foozle$/) {
# code for 'foozle' command
}
}
sub init {
my $o = shift;
$o->add_handlers("run_fuzz", "run_foozle");
}
There are other ways to do this. You could write a "catch_run" routine
and do the same thing from there. You'd have to override "comp_" so
that it would complete on "foozle" and "fuzz". The advantage to this
method is that it adds the methods to the list of commands, so they
show up in the help menu and you get completion for free.
Removing Commands from Your Shell
You're probably thinking "just don't write them". But remember, you can
inherit from another shell class, and that parent may define commands
you want to disable. Term::Shell provides a simple method to make
itself forget about commands it already knows about:
1. remove_commands()
Removes all handlers associated with the given command (or list of
commands).
For example, Term::Shell comes with two commands ("exit" and
"help") implemented with seven handlers:
1. smry_exit()
2. help_exit()
3. run_exit()
4. smry_help()
5. help_help()
6. comp_help()
7. run_help()
If you want to create a shell that doesn't implement the "help"
command, your code might look something like this example:
package MyShell;
use base qw(Term::Shell);
sub init {
my $o = shift;
$o->remove_commands("help");
}
# ... define more handlers here ...
2. remove_handlers()
Removes the given handler (or handlers) from the list of defined
commands. You have to specify a full handler name, including the
'run_' prefix. You can obviously specify any of the other prefixes
too.
If you wanted to remove the help for the "exit" command, but
preserve the command itself, your code might look something like
this:
package MyShell;
use base qw(Term::Shell);
sub init {
my $o = shift;
$o->remove_handlers("help_exit");
}
# ... define more handlers here ...
Cover Your Tracks
If you do remove built in commands, you should be careful not to let
Term::Shell print references to them. Messages like this are guaranteed
to confuse people who use your shell:
shell> help
Unknown command 'help'; type 'help' for a list of commands.
Here's the innocuous looking code:
package MyShell;
use base qw(Term::Shell);
sub init {
my $o = shift;
$o->remove_commands("help");
}
MyShell->new->cmdloop;
The problem is that Term::Shell has to print an error message, and by
default it tells the user to use the "help" command to see what's
available. If you remove the "help" command, you still have to clean up
after yourself and tell Term::Shell to change its error messages:
1. msg_unknown_cmd()
Called when the user has entered an unrecognized command, and no
action was available to satisfy it. It receives the object and the
command typed by the user as its arguments. It should return an
error message; by default, it is defined thusly:
sub msg_unknown_cmd {
my ($o, $cmd) = @_;
<<END;
Unknown command '$cmd'; type 'help' for a list of commands.
END
}
2. msg_ambiguous_cmd()
Called when the user has entered a command for which more than
handler exists. (For example, if both "quit" and "query" are
commands, then "qu" is an ambiguous command, because it could be
either.) It receives the object, the command, and the possible
commands which could complete it. It should return an error
message; by default it is defined thusly:
sub msg_ambiguous_cmd {
my ($o, $cmd, @c) = @_;
local $" = "\n\t";
<<END;
Ambiguous command '$cmd': possible commands:
@c
END
}
The Term::Shell API
Shell classes can use any of the methods in this list. Any other
methods in Term::Shell may change.
1. new()
Creates a new Term::Shell object. It currently does not use its
arguments. The arguments are saved in '$o->{API}{args}', in case
you want to use them later.
my $sh = Term::Shell->new(@arbitrary_args);
2. cmd()
cmd($txt);
Invokes $txt as if it had been typed in at the prompt.
$sh->cmd("echo 1 2 3");
3. cmdloop()mainloop()
Repeatedly prompts the user, reads a line, parses it, and invokes a
handler. Uses "cmd()" internally.
MyShell->new->cmdloop;
mainloop() is a synonym for cmdloop(), provided for backwards
compatibility. Earlier (unreleased) versions of Term::Shell have
only provided mainloop(). All documentation and examples use
cmdloop() instead.
4. init()fini()
Do any initialization or cleanup you need at shell creation
(init()) and destruction (fini()) by defining these methods.
No parameters are passed.
5. preloop()postloop()
Do any initialization or cleanup you need at shell startup
(preloop()) and shutdown (postloop()) by defining these methods.
No parameters are passed.
6. precmd()postcmd()
Do any initialization or cleanup before and after calling each
handler.
The parameters are:
1. $handler
A reference to the name of the handler that is about to be
executed.
Passed by reference so you can control which handler will be
called.
2. $cmd
A reference to the command as the user typed it.
Passed by reference so you can set the command. (If the handler
is a "catch_" command, it can be fooled into thinking the user
typed some other command, for example.)
3. $args
The arguments as typed by the user. This is passed as an array
reference so that you can manipulate the arguments received by
the handler.
sub precmd {
my $o = shift;
my ($handler, $cmd, @args) = @_;
# ...
}
7. stoploop()
Sets a flag in the Term::Shell object that breaks out of cmdloop().
Note that cmdloop() resets this flag each time you call it, so code
like this will work:
my $sh = MyShell->new;
$sh->cmdloop; # an interactive session
$sh->cmdloop; # prompts the user again
Term::Shell's built-in run_exit() command just calls stoploop().
8. idle()
If you set "check_idle" to a non-zero number (see "The Term::Shell
Object") then this method is called every "check_idle" seconds. The
idle() method defined in Term::Shell does nothing -- it exists only
to be redefined in subclasses.
package MyShell;
use base qw(Term::Shell);
sub init {
my $o = shift;
$o->{API}{check_idle} = 0.1; # 10/s
}
sub idle {
print "Idle!\n";
}
9. prompt_str()
Returns a string to be used as the prompt. prompt_str() is called
just before calling the readline() method of Term::ReadLine. If you
do not override this method, the string `shell> ' is used.
package MyShell;
use base qw(Term::Shell);
sub prompt_str { "search> " }
10. prompt()Term::Shell provides this method for convenience. It's common for a
handler to ask the user for more information. This method makes it
easy to provide the user with a different prompt and custom
completions provided by you.
The prompt() method takes the following parameters:
1. $prompt
The prompt to display to the user. This can be any string you
want.
2. $default
The default value to provide. If the user enters a blank line
(all whitespace characters) then the this value will be
returned.
Note: unlike ExtUtils::MakeMaker's prompt(), Term::Shell's
prompt() does not modify $prompt to indicate the $default
response. You have to do that yourself.
3. $completions
An optional list of completion values. When the user hits
<TAB>, Term::Shell prints the completions which match what
they've typed so far. Term::Shell does not enforce that the
user's response is one of these values.
4. $casei
An optional boolean value which indicates whether the
completions should be matched case-insensitively or not. A true
value indicates that "FoO" and "foo" should be considered the
same.
prompt() returns the unparsed line to give you maximum flexibility.
If you need the line parsed, use the line_parsed() method on the
return value.
11. cmd_prefix()cmd_suffix()
These methods should return a prefix and suffix for commands,
respectively. For instance, an IRC client will have a prefix of
"/". Most shells have an empty prefix and suffix.
12. page()
page($txt)
Prints $txt through a pager, prompting the user to press a key for
the next screen full of text.
13. line()line_parsed()
Although "run_foo()" is called with the parsed arguments from the
command-line, you may wish to see the raw command-line. This is
available through the line() method. If you want to retrieve the
parsed line again, use line_parsed().
line_parsed() accepts an optional string parameter: the line to
parse. If you have your own line to parse, you can pass it to
line_parsed() and get back a list of arguments. This is useful
inside completion methods, since you don't get a parsed list there.
14. run()
If you want to run another handler from within a handler, and you
have pre-parsed arguments, use run() instead of cmd(). cmd() parses
its parameter, whereas run() takes each element as a separate
parameter.
It needs the name of the action to run and any arguments to pass to
the handler.
Term::Shell uses this method internally to invoke command handlers.
15. help()
If you want to get the raw text of a help message, use help(). It
needs the name of the help topic and any arguments to pass to the
handler.
Term::Shell uses this method internally to invoke help handlers.
16. summary()
If you want to get the summary text of an action, use summary(). It
needs the name of the action.
Term::Shell uses this method internally to display the help page.
17. possible_actions()
You will probably want this method in comp_foo().
possible_actions() takes a word and a list, and returns a list of
possible matches. Term::Shell uses this method internally to decide
which handler to run when the user enters a command.
There are several arguments, but you probably won't use them all in
the simple cases:
1. $needle
The (possible incomplete) word to try to match against the list
of actions (the haystack).
2. $type
The type with which to prefix $action. This is useful when
completing a real action -- you have to specify whether you
want it to look for "run_" or "help_" or something else. If you
leave it blank, it will use $action without prefixing it.
3. $strip
If you pass in a true value here, possible_actions() will
remove an initial $type from the beginning of each result
before returning the results. This is useful if you want to
know what the possible "run_" commands are, but you don't want
to have the "run_" in the final result.
If you do not specify this argument, it uses '0' (the default
is not to strip the results).
4. $haystack
You can pass in a reference to a list of strings here. Each
string will be compared with $needle.
If you do not specify this argument, it uses the list of
handlers. This is how Term::Shell matches commands typed in by
the user with command handlers written by you.
18. print_pairs()
This overloaded beast is used whenever Term::Shell wants to print a
set of keys and values. It handles wrapping long values, indenting
the whole thing, inserting the separator between the key and value,
and all the rest.
There are lots of parameters, but most of them are optional:
1. $keys
A reference to a list of keys to print.
2. $values
A reference to a list of values to print.
3. $sep
The string used to separate the keys and values. If omitted, ':
' is used.
4. $left
The justification to be used to line up the keys. If true, the
keys will be left-justified. If false or omitted, the keys will
be right-justified.
5. $ind
A string used to indent the whole paragraph. Internally,
print_pairs() uses length(), so you shouldn't use tabs in the
indent string. If omitted, the empty string is used (no
indent).
6. $len
An integer which describes the minimum length of the keys.
Normally, print_pairs() calculates the longest key and assigns
the column width to be as wide as the longest key plus the
separator. You can force the column width to be larger using
$len. If omitted, 0 is used.
7. $wrap
A boolean which indicates whether the value should be text-
wrapped using Text::Autoformat. Text is only ever wrapped if it
contains at least one space. If omitted, 0 is used.
8. $cols
An integer describing the number of columns available on the
current terminal. Normally 78 is used, or the environment
variable COLUMNS, but you can override the number here to
simulate a right-indent.
19. term()
Returns the underlying "Term::ReadLine" object used to interact
with the user. You can do powerful things with this object; in
particular, you will cripple Term::Shell's completion scheme if you
change the completion callback function.
20. process_esc()
This method may be overridden to provide shell-like escaping of
backslashes inside quoted strings. It accepts two parameters:
1. $c
The character which was escaped by a backslash.
2. $quote
The quote character used to delimit this string. Either """ or
"'".
This method should return the string which should replace the
backslash and the escaped character.
By default, process_esc() uses escaping rules similar to Perl's
single-quoted string:
1. Escaped backslashes return backslashes. The string "123\\456"
returns "123\456".
2. Escaped quote characters return the quote character (to allow
quote characters in strings). The string "abc\"def" returns
"abc"def".
3. All other backslashes are returned verbatim. The string
"123\456" returns "123\456".
Term::Shell's quote characters cannot be overridden, unless you
override line_parsed(): they are """ or "'". This may change in a
future version of Term::Shell.
21. add_handlers()
See "Adding Commands to Your Shell" for information on
add_handlers().
22. remove_commands()remove_handlers()
See "Removing Commands from Your Shell" for information on
remove_handlers().
The Term::Shell ObjectTerm::Shell creates a hash based Perl object. The object contains
information like what handlers it found, the underlying Term::ReadLine
object, and any arguments passed to the constructor.
This hash is broken into several subhashes. The only two subhashes that
a Shell should ever use are $o->{API} and $o->{SHELL}. The first one
contains all the information that Term::Shell has gathered for you. The
second one is a private area where your Shell can freely store data
that it might need later on.
This section will describe all the Term::Shell object "API" attributes:
The args Attribute
This an array reference containing any arguments passed to the
Term::Shell constructor.
The case_ignore Attribute
This boolean controls whether commands should be matched without regard
to case. If this is true, then typing "FoO" will have the same effect
as typing "foo".
Defaults to true on MSWin32, and false on other platforms.
The class Attribute
The class of the object. This is probably the package containing the
definition of your shell, but if someone subclasses your shell, it's
their class.
The command Attribute
Whenever Term::Shell invokes an action, it stores information about the
action in the "command" attribute. Information about the last "run"
action to be invoked is stored in $o->{API}{command}{run}. The
information itself is stored in a subhash containing these fields:
name
The name of the command, as typed by the user.
found
The a boolean value indicating whether a handler could be found.
handler
The full name of the handler, if found.
Note that this facility only stores information about the last action
to be executed. It's good enough for retrieving the information about
the last handler which ran, but not for much else.
The following example shows a case where "run_foo()" calls "run_add()",
and prints its return value (in this case, 42).
sub run_foo {
my $o = shift;
my $sum = $o->run("add", 21, 21);
print "21 + 21 = ", $sum, "\n";
}
sub run_add {
my $o = shift;
my $sum = 0;
$sum += $_ for @_;
print "add(): sum = $sum\n";
return $sum;
}
At the end of run_foo(), $o->{API}{command}{run}{handler} contains the
string "run_add".
The match_uniq Attribute
This boolean controls whether the user can type in only enough of the
command to make it unambiguous. If true, then if the shell has the
commands "foo" and "bar" defined, the user can type "f" to run "foo",
and "b" to run "bar".
Defaults to true.
The readline Attribute
Which Term::ReadLine module is being used. Currently, this is always
one of "Term::ReadLine::Stub", "Term::ReadLine::Perl", or
"Term::ReadLine::Gnu".
The script Attribute
The name of the script that invoked your shell.
The version Attribute
The version of Term::Shell you are running under.
BUGS AND DEFICIENCIES
There are bound to be some bugs lurking about.
If you find bugs, please send them to "NEILW@cpan.org".
SEE ALSO
For more information about the underlying ReadLine module, see
Term::ReadLine. You may also want to look at Term::ReadLine::Gnu and
Term::ReadLine::Perl.
For more information about the underlying formatter used by
print_pairs(), see Text::Autoformat.
The API for Term::Shell was inspired by (gasp!) a Python package called
"cmd". For more information about this package, please look in the
Python Library Reference, either in your Python distribution or at
http://www.python.org/doc/current/lib/module-cmd.html
AUTHOR
Neil Watkiss (NEILW@cpan.org)
COPYRIGHT
Copyright (c) 2001, Neil Watkiss. All Rights Reserved.
All Rights Reserved. This module is free software. It may be used,
redistributed and/or modified under the same terms as Perl itself.
See http://www.perl.com/perl/misc/Artistic.html
POD ERRORS
Hey! The above document had some coding errors, which are explained
below:
Around line 211:
You forgot a '=back' before '=head2'
Around line 244:
=back without =over
perl v5.14.0 2007-02-23 Term::Shell(3)
