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

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,
			   timeout => 20 )
	   ) {
	       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
   $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.

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, 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 right 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 "errorcode"
	   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 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.

   $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
       seperate arguments to the "echo" function.

       __END__

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 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 and "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 loose the significance
	   of the whitespace.  Therefor, "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'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.

       Interleaving STDOUT/STDERR
	   Neither IPC::Run nor IPC::Open3 can interleave STDOUT and STDERR.
	   For short bursts of output from a program, ie 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 1 line on each, namely '13' on STDOUT
	   and '24' on STDERR.

	   It should have been 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", "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 <bug-ipc-cmd@rt.cpan.org>.

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

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

perl v5.10.1			  2009-06-23			   IPC::Cmd(3)
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