NAME

IPC::Cmd - finding and running system commands made easy

SYNOPSIS

use IPC::Cmd qw[can_run run];

my $full_path = can_run('wget') or warn 'wget is not installed!';


### commands can be arrayrefs or strings ###
my $cmd = "$full_path -b theregister.co.uk";
my $cmd = [$full_path, '-b', 'theregister.co.uk'];

### in scalar context ###
my $buffer;
if( scalar run( command => $cmd,
                verbose => 0,
                buffer  => \$buffer )
) {
    print "fetched webpage successfully\n";
}


### in list context ###
my( $success, $error_code, $full_buf, $stdout_buf, $stderr_buf ) =
        run( command => $cmd, verbose => 0 );

if( $success ) {
    print "this is what the command printed:\n";
    print join "", @$full_buf;
}


### don't have IPC::Cmd be verbose, ie don't print to stdout or
### stderr when running commands -- default is '0'
$IPC::Cmd::VERBOSE = 0;

DESCRIPTION

IPC::Cmd allows you to run commands, interactively if desired, platform independent but have them still work.

The can_run function can tell you if a certain binary is installed and if so where, whereas the run function can actually execute any of the commands you give it and give you a clear return value, as well as adhere to your verbosity settings.

FUNCTIONS

can_run

can_run takes but a single argument: the name of a binary you wish to locate. can_run works much like the unix binary which or the bash command type, which scans through your path, looking for the requested binary .

Unlike which and type, this function is platform independent and will also work on, for example, Win32.

It will return the full path to the binary you asked for if it was found, or undef if it was not.

run

run takes 3 arguments:

command

This is the command to execute. It may be either a string or an array reference. This is a required argument.

See CAVEATS for remarks on how commands are parsed and their limitations.

verbose

This controls whether all output of a command should also be printed to STDOUT/STDERR or should only be trapped in buffers (NOTE: buffers require IPC::Run to be installed or your system able to work with IPC::Open3).

It will default to the global setting of $IPC::Cmd::VERBOSE, which by default is 0.

buffer

This will hold all the output of a command. It needs to be a reference to a scalar. Note that this will hold both the STDOUT and STDERR messages, and you have no way of telling which is which. If you require this distinction, run the run command in list context and inspect the individual buffers.

Of course, this requires that the underlying call supports buffers. See the note on buffers right above.

run will return a simple true or false when called in scalar context. In list context, you will be returned a list of the following items:

success

A simple boolean indicating if the command executed without errors or not.

errorcode

If the first element of the return value (success) was 0, then some error occurred. This second element is the error code the command you requested exited with, if available.

full_buffer

This is an arrayreference containing all the output the command generated. Note that buffers are only available if you have IPC::Run installed, or if your system is able to work with IPC::Open3 -- See below). This element will be undef if this is not the case.

out_buffer

This is an arrayreference containing all the output sent to STDOUT the command generated. Note that buffers are only available if you have IPC::Run installed, or if your system is able to work with IPC::Open3 -- See below). This element will be undef if this is not the case.

error_buffer

This is an arrayreference containing all the output sent to STDERR the command generated. Note that buffers are only available if you have IPC::Run installed, or if your system is able to work with IPC::Open3 -- See below). This element will be undef if this is not the case.

run will try to execute your command using the following logic:

• If you are not on windows 98 and have IPC::Run installed, use that to execute the command. You will have the full output available in buffers, interactive commands are sure to work and you are guaranteed to have your verbosity settings honored cleanly.

• Otherwise, if you are not on MSWin32 or Cygwin, try to execute the command by using IPC::Open3. Buffers will be available, interactive commands will still execute cleanly, and also your verbosity settings will be adhered to nicely;

• Otherwise, if you have the verbose argument set to true, we fall back to a simple system() call. We cannot capture any buffers, but interactive commands will still work.

• Otherwise we will try and temporarily redirect STDERR and STDOUT, do a system() call with your command and then re-open STDERR and STDOUT. This is the method of last resort and will still allow you to execute your commands cleanly. However, no buffers will be available.

Global Variables

The behaviour of IPC::Cmd can be altered by changing the following global variables:

$IPC::Cmd::VERBOSE

This controls whether IPC::Cmd will print any output from the commands to the screen or not. The default is 0;

$IPC::Cmd::USE_IPC_RUN

This variable controls whether IPC::Cmd will try to use IPC::Run when available and suitable. Defaults to true.

$IPC::Cmd::USE_IPC_OPEN3

This variable controls whether IPC::Cmd will try to use IPC::Open3 when available and suitable. Defaults to true.

Caveats

Whitespace

When you provide a string as this argument, the string will be split on whitespace to determine the individual elements of your command. Although this will usually just Do What You Mean, it may break if you have files or commands with whitespace in them.

If you do not wish this to happen, you should provide an array reference, where all parts of your command are already separated out. Note however, if there's extra or spurious whitespace in these parts, the parser or underlying code may not interpret it correctly, and cause an error.

Example: The following code

gzip -cdf foo.tar.gz | tar -xf -

should either be passed as

"gzip -cdf foo.tar.gz | tar -xf -"

or as

['gzip', '-cdf', 'foo.tar.gz', '|', 'tar', '-xf', '-']

But take care not to pass it as, for example

['gzip -cdf foo.tar.gz', '|', 'tar -xf -']

Since this will lead to issues as described above.

IO Redirect

Currently it is too complicated to parse your command for IO Redirections. For capturing STDOUT or STDERR there is a work around however, since you can just inspect your buffers for the contents.

IPC::Run buffer capture bug

Due to a bug in IPC::Run versions upto and including the latest one at the time of writing (0.78), run() calls executed via IPC::Run will not be able to differentiate between STDOUT and STDERR output when special characters are present in the command (like <,>,| and &); All output will be caught in the STDERR buffer.

Note that this is only a problem if you use the long output of run() and not if you provide the buffer option to the command.

If this limitation is not acceptable to you, consider setting the global variable $IPC::Cmd::USE_IPC_RUN to false.

See Also

IPC::Run, IPC::Open3

AUTHOR

This module by Jos Boumans <kane@cpan.org>.

ACKNOWLEDGEMENTS

Thanks to James Mastros and Martijn van der Streek for their help in getting IPC::Open3 to behave nicely.

COPYRIGHT

This module is copyright (c) 2002,2003,2004 Jos Boumans <kane@cpan.org>. All rights reserved.

This library is free software; you may redistribute and/or modify it under the same terms as Perl itself.

cpanm IPC::Cmd

perl -MCPAN -e shell
install IPC::Cmd