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 IPC::Run 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:
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.
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.
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.
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:
A simple boolean indicating if the command executed without errors or not.
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.
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.
This is an array reference containing all the output sent to STDOUT the command generated. The notes from full_buffer apply.
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.
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.
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:
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:
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,
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 IPC::Run when available and suitable.
This variable controls whether IPC::Cmd will try to use IPC::Open3 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.
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.
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.
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.
Neither IPC::Run nor IPC::Open3 can interleave STDOUT and STDERR. For short bursts of output from a program, e.g. this sample,
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.
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.
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.