| IPC::Cmd - finding and running system commands made easy |
IPC::Cmd - finding and running system commands made easy
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;
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.
Utility function that tells you if IPC::Run is available.
If the verbose flag is passed, it will print diagnostic messages
if the IPC::Run manpage can not be found or loaded.
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.
Utility function that tells you if IPC::Cmd is capable of
capturing buffers in it's current configuration.
Utility function that tells you if IPC::Cmd is capable of
providing run_forked on the current platform.
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.
run takes 4 arguments:
See Caveats for remarks on how commands are parsed and their limitations.
It will default to the global setting of $IPC::Cmd::VERBOSE,
which by default is 0.
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.
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) 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.
undef.
See the HOW IT WORKS section below to see how IPC::Cmd decides
what modules or function calls to use when issuing a command.
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:
timeoutchild_stdinSTDIN of the executed program.
stdout_handlerstderr_handlerwait_loop_callbackrun_forked waits for the external to finish or fail).
It is useful to stop running external process before it ends
by itself, e.g.
my $r = run_forked("some external command", {
'wait_loop_callback' => sub {
if (condition) {
kill(1, $$);
}
},
'terminate_on_signal' => 'HUP',
});
Combined with stdout_handler and stderr_handler allows terminating
external command based on its output. Could also be used as a timer
without engaging with alarm (signals).
Remember that this code could be called every millisecond (depending on the output which external command generates), so try to make it as lightweight as possible.
discard_outputterminate_on_parent_sudden_deathrun_forked will return a HASHREF with the following keys:
exit_codetimeoutstdoutdiscard_output was used; it's always defined!)
stderrdiscard_output was used; it's always defined!)
mergeddiscard_output was used; it's always defined!)
err_msg
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.
run will try to execute your command using the following logic:
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
the IPC::Open3 manpage. Buffers will be available on all platforms,
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.
The behaviour of IPC::Cmd can be altered by changing the following global variables:
This controls whether IPC::Cmd will print any output from the commands to the screen or not. The default is 0.
This variable controls whether IPC::Cmd will try to use the IPC::Run manpage when available and suitable.
This variable controls whether IPC::Cmd will try to use the IPC::Open3 manpage when available and suitable. Defaults to true.
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.
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.
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.
system()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.
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.
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.
the IPC::Run manpage, the IPC::Open3 manpage
Thanks to James Mastros and Martijn van der Streek for their help in getting the IPC::Open3 manpage to behave nicely.
Thanks to Petya Kohts for the run_forked code.
Please report bugs or other issues to <bug-ipc-cmd@rt.cpan.org>.
Original author: Jos Boumans <kane@cpan.org>. Current maintainer: Chris Williams <bingos@cpan.org>.
This library is free software; you may redistribute and/or modify it under the same terms as Perl itself.
| IPC::Cmd - finding and running system commands made easy |