IPC::Cmd (3)

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========================================================================

(The comments found at the beginning of the groff file "man3/IPC::Cmd.3perl".)

NAME

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

SYNOPSIS

    use IPC::Cmd qw[can_run run run_forked];

    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,
                    timeout => 20 )
    ) {
        print "fetched webpage successfully: $buffer\n";
    }

    ### in list context ###
    my( $success, $error_message, $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;
    }

    ### run_forked example ###
    my $result = run_forked("$full_path -q -O - theregister.co.uk", {'timeout' => 20});
    if ($result->{'exit_code'} eq 0 && !$result->{'timeout'}) {
        print "this is what wget returned:\n";
        print $result->{'stdout'};
    }

    ### 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 platform independently, interactively if desired, 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

$ipc_run_version = 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.

$ipc_open3_version = 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.

$bool = IPC::Cmd->can_use_run_forked

Utility function that tells you if "IPC::Cmd" is capable of providing "run_forked" on the current platform.

FUNCTIONS

$path = can_run(

PROGRAM

);

"can_run" takes only one 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.

If called in a scalar context it will return the full path to the binary you asked for if it was found, or "undef" if it was not.

If called in a list context and the global variable $INSTANCES is a true value, it will return a list of the full paths to instances of the binary where found in "PATH", or an empty list if it was not found.

$ok | ($ok, $err, $full_buf, $stdout_buff, $stderr_buff) = run( command =>

COMMAND,

[verbose =>

BOOL,

buffer => \$SCALAR, timeout =>

DIGIT

] );

"run" takes 4 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 above.

timeout

Sets the maximum time the command is allowed to run before aborting, using the built-in "alarm()" call. If the timeout is triggered, the "errorcode" in the return value will be set to an object of the "IPC::Cmd::TimeOut" class. See the ``error message'' section below for details.

Defaults to 0, meaning no timeout is set.

"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.

error message

If the first element of the return value ("success") was 0, then some error occurred. This second element is the error message the command you requested exited with, if available. This is generally a pretty printed value of $? or $@. See "perldoc perlvar" for details on what they can contain. If the error was a timeout, the "error message" will be prefixed with the string "IPC::Cmd::TimeOut", the timeout class.

full_buffer

This is an array reference 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). Otherwise, this element will be "undef".

out_buffer

This is an array reference containing all the output sent to

STDOUT

the command generated. The notes from ``full_buffer'' apply.

error_buffer

This is an arrayreference containing all the output sent to

STDERR

the command generated. The notes from ``full_buffer'' apply.

See the ``

section below to see how "IPC::Cmd" decides what modules or function calls to use when issuing a command.

$hashref = run_forked(

COMMAND,

{ child_stdin =>

SCALAR,

timeout =>

DIGIT,

stdout_handler =>

CODEREF,

stderr_handler =>

CODEREF

} );

"run_forked" is used to execute some program or a coderef, optionally feed it with some input, get its return code and output (both stdout and stderr into separate buffers). In addition, it allows to terminate the program if it takes too long to finish.

The important and distinguishing feature of run_forked is execution timeout which at first seems to be quite a simple task but if you think that the program which you're spawning might spawn some children itself (which in their turn could do the same and so on) it turns out to be not a simple issue.

"run_forked" is designed to survive and successfully terminate almost any long running task, even a fork bomb in case your system has the resources to survive during given timeout.

This is achieved by creating separate watchdog process which spawns the specified program in a separate process session and supervises it: optionally feeds it with input, stores its exit code, stdout and stderr, terminates it in case it runs longer than specified.

Invocation requires the command to be executed or a coderef and optionally a hashref of options:

timeout

Specify in seconds how long to run the command before it is killed with

SIG_KILL \fIs0(9), which effectively terminates it and all of its children (direct or indirect).

child_stdin

Specify some text that will be passed into the "STDIN" of the executed program.

stdout_handler

Coderef of a subroutine to call when a portion of data is received on

  use IPC::Cmd qw[run QUOTE];
  my $cmd = q[echo ] . QUOTE . q[foo bar] . QUOTE;