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IPC::Cmd(3pm)          Perl Programmers Reference Guide          IPC::Cmd(3pm)




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 "HOW IT WORKS" 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 (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 STDOUT from the executing program.

       "stderr_handler"
           Coderef of a subroutine to call when a portion of data is received
           on STDERR from the executing program.

       "discard_output"
           Discards the buffering of the standard output and standard errors
           for return by run_forked().  With this option you have to use the
           std*_handlers to read what the command outputs.  Useful for
           commands that send a lot of output.

       "terminate_on_parent_sudden_death"
           Enable this option if you wish all spawned processes to be killed
           if the initially spawned process (the parent) is killed or dies
           without waiting for child processes.

       "run_forked" will return a HASHREF with the following keys:

       "exit_code"
           The exit code of the executed program.

       "timeout"
           The number of seconds the program ran for before being terminated,
           or 0 if no timeout occurred.

       "stdout"
           Holds the standard output of the executed command (or empty string
           if there was no STDOUT output or if "discard_output" was used; it's
           always defined!)

       "stderr"
           Holds the standard error of the executed command (or empty string
           if there was no STDERR output or if "discard_output" was used; it's
           always defined!)

       "merged"
           Holds the standard output and error of the executed command merged
           into one stream (or empty string if there was no output at all or
           if "discard_output" was used; it's always defined!)

       "err_msg"
           Holds some explanation in the case of an error.

   $q = QUOTE
       Returns the character used for quoting strings on this platform. This
       is usually a "'" (single quote) on most systems, but some systems use
       different quotes. For example, "Win32" uses """ (double quote).

       You can use it as follows:

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

       This makes sure that "foo bar" is treated as a string, rather than two
       separate arguments to the "echo" function.


HOW IT WORKS

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

       o   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.

       o   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,
           interactive commands will still execute cleanly, and also your
           verbosity settings will be adhered to nicely;

       o   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.

       o   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.

   $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.

   $IPC::Cmd::INSTANCES
       This variable controls whether "can_run" will return all instances of
       the binary it finds in the "PATH" when called in a list context.

       Defaults to false, set to true to enable the described behaviour.

   $IPC::Cmd::ALLOW_NULL_ARGS
       This variable controls whether "run" will remove any empty/null
       arguments it finds in command arguments.

       Defaults to false, so it will remove null arguments. Set to true to
       allow them.


Caveats

       Whitespace and IPC::Open3 / system()
           When using "IPC::Open3" or "system", if you provide a string as the
           "command" argument, it is assumed to be appropriately escaped. You
           can use the "QUOTE" constant to use as a portable quote character
           (see above).  However, if you provide an array reference, special
           rules apply:

           If your command contains special characters (< > | &), it will be
           internally stringified before executing the command, to avoid that
           these special characters are escaped and passed as arguments
           instead of retaining their special meaning.

           However, if the command contained arguments that contained
           whitespace, stringifying the command would lose the significance of
           the whitespace.  Therefore, "IPC::Cmd" will quote any arguments
           containing whitespace in your command if the command is passed as
           an arrayref and contains special characters.

       Whitespace and IPC::Run
           When using "IPC::Run", if you provide a string as the "command"
           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 are extra or spurious whitespaces 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.

       Interleaving STDOUT/STDERR
           Neither IPC::Run nor IPC::Open3 can interleave STDOUT and STDERR.
           For short bursts of output from a program, e.g. this sample,

               for ( 1..4 ) {
                   $_ % 2 ? print STDOUT $_ : print STDERR $_;
               }

           IPC::[Run|Open3] will first read all of STDOUT, then all of STDERR,
           meaning the output looks like '13' on STDOUT and '24' on STDERR,
           instead of

               1
               2
               3
               4

           This has been recorded in rt.cpan.org as bug #37532: Unable to
           interleave STDOUT and STDERR.


See Also

       IPC::Run(3), IPC::Open3(3)


ACKNOWLEDGEMENTS

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

       Thanks to Petya Kohts for the "run_forked" code.


BUG REPORTS

       Please report bugs or other issues to <bug-ipc-cmd@rt.cpan.org>.


AUTHOR

       Original author: Jos Boumans <kane@cpan.org>.  Current maintainer:
       Chris Williams <bingos@cpan.org>.


COPYRIGHT

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



perl v5.26.1                      2017-07-18                     IPC::Cmd(3pm)

perl 5.26.1 - Generated Sun Nov 5 15:43:31 CST 2017
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