Content-type: text/html Man page of IPC::Cmd

IPC::Cmd

Section: Perl Programmers Reference Guide (3perl)
Updated: 2007-12-18
Index Return to Main Contents
 

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: $buffer\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;
    }

    ### check for features
    print "IPC::Open3 available: "  . IPC::Cmd->can_use_ipc_open3;      
    print "IPC::Run available: "    . IPC::Cmd->can_use_ipc_run;      
    print "Can capture buffer: "    . IPC::Cmd->can_capture_buffer;     

    ### 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.  

CLASS METHODS

 

$bool = IPC::Cmd->can_use_ipc_run( [VERBOSE] )

Utility function that tells you if "IPC::Run" is available. If the verbose flag is passed, it will print diagnostic messages if "IPC::Run" can not be found or loaded.  

$bool = IPC::Cmd->can_use_ipc_open3( [VERBOSE] )

Utility function that tells you if "IPC::Open3" is available. If the verbose flag is passed, it will print diagnostic messages if "IPC::Open3" can not be found or loaded.  

$bool = IPC::Cmd->can_capture_buffer

Utility function that tells you if "IPC::Cmd" is capable of capturing buffers in it's current configuration.  

FUNCTIONS

 

$path = can_run( PROGRAM );

"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.  

$ok | ($ok, $err, $full_buf, $stdout_buff, $stderr_buff) = run( command => COMMAND, [verbose => BOOL, buffer => \$SCALAR] );

"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.

See the "HOW IT WORKS" Section below to see how "IPC::Cmd" decides what modules or function calls to use when issuing a command.  

HOW IT WORKS

"run" will try to execute your command using the following logic:
If you have "IPC::Run" installed, and the variable $IPC::Cmd::USE_IPC_RUN is set to true (See the "GLOBAL VARIABLES" Section) 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 the variable $IPC::Cmd::USE_IPC_OPEN3 is set to true (See the "GLOBAL VARIABLES" Section), try to execute the command using "IPC::Open3". Buffers will be available on all platforms except "Win32", 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 if you are on "Win32".  

$IPC::Cmd::USE_IPC_OPEN3

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

$IPC::Cmd::WARN

This variable controls whether run time warnings should be issued, like the failure to load an "IPC::*" module you explicitly requested.

Defaults to true. Turn this off at your own risk.  

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.
 

See Also

"IPC::Run", "IPC::Open3"  

ACKNOWLEDGEMENTS

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

BUG REPORTS

Please report bugs or other issues to <[email protected]>.  

AUTHOR

This module by Jos Boumans <[email protected]>.  

COPYRIGHT

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


 

Index

NAME
SYNOPSIS
DESCRIPTION
CLASS METHODS
$bool = IPC::Cmd->can_use_ipc_run( [VERBOSE] )
$bool = IPC::Cmd->can_use_ipc_open3( [VERBOSE] )
$bool = IPC::Cmd->can_capture_buffer
FUNCTIONS
$path = can_run( PROGRAM );
$ok | ($ok, $err, $full_buf, $stdout_buff, $stderr_buff) = run( command => COMMAND, [verbose => BOOL, buffer => \$SCALAR] );
HOW IT WORKS
Global Variables
$IPC::Cmd::VERBOSE
$IPC::Cmd::USE_IPC_RUN
$IPC::Cmd::USE_IPC_OPEN3
$IPC::Cmd::WARN
Caveats
See Also
ACKNOWLEDGEMENTS
BUG REPORTS
AUTHOR
COPYRIGHT

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Time: 04:14:15 GMT, September 24, 2010