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IPC::System::Simple - phpMan
IPC::System::Simple(3pm) User Contributed Perl Documentation IPC::System::Simple(3pm)
NAME
IPC::System::Simple - Run commands simply, with detailed diagnostics
SYNOPSIS
use IPC::System::Simple qw(system systemx capture capturex);
system("some_command"); # Command succeeds or dies!
system("some_command",@args); # Succeeds or dies, avoids shell if @args
systemx("some_command",@args); # Succeeds or dies, NEVER uses the shell
# Capture the output of a command (just like backticks). Dies on error.
my $output = capture("some_command");
# Just like backticks in list context. Dies on error.
my @output = capture("some_command");
# As above, but avoids the shell if @args is non-empty
my $output = capture("some_command", @args);
# As above, but NEVER invokes the shell.
my $output = capturex("some_command", @args);
my @output = capturex("some_command", @args);
DESCRIPTION
Calling Perl's in-built "system()" function is easy, determining if it was successful is
hard. Let's face it, $? isn't the nicest variable in the world to play with, and even if
you do check it, producing a well-formatted error string takes a lot of work.
"IPC::System::Simple" takes the hard work out of calling external commands. In fact, if
you want to be really lazy, you can just write:
use IPC::System::Simple qw(system);
and all of your "system" commands will either succeed (run to completion and return a zero
exit value), or die with rich diagnostic messages.
The "IPC::System::Simple" module also provides a simple replacement to Perl's backticks
operator. Simply write:
use IPC::System::Simple qw(capture);
and then use the "capture()" command just like you'd use backticks. If there's an error,
it will die with a detailed description of what went wrong. Better still, you can even
use "capturex()" to run the equivalent of backticks, but without the shell:
use IPC::System::Simple qw(capturex);
my $result = capturex($command, @args);
If you want more power than the basic interface, including the ability to specify which
exit values are acceptable, trap errors, or process diagnostics, then read on!
ADVANCED SYNOPSIS
use IPC::System::Simple qw(
capture capturex system systemx run runx $EXITVAL EXIT_ANY
);
# Run a command, throwing exception on failure
run("some_command");
runx("some_command",@args); # Run a command, avoiding the shell
# Do the same thing, but with the drop-in system replacement.
system("some_command");
systemx("some_command", @args);
# Run a command which must return 0..5, avoid the shell, and get the
# exit value (we could also look at $EXITVAL)
my $exit_value = runx([0..5], "some_command", @args);
# The same, but any exit value will do.
my $exit_value = runx(EXIT_ANY, "some_command", @args);
# Capture output into $result and throw exception on failure
my $result = capture("some_command");
# Check exit value from captured command
print "some_command exited with status $EXITVAL\n";
# Captures into @lines, splitting on $/
my @lines = capture("some_command");
# Run a command which must return 0..5, capture the output into
# @lines, and avoid the shell.
my @lines = capturex([0..5], "some_command", @args);
ADVANCED USAGE
run() and system()
"IPC::System::Simple" provides a subroutine called "run", that executes a command using
the same semantics is Perl's built-in "system":
use IPC::System::Simple qw(run);
run("cat *.txt"); # Execute command via the shell
run("cat","/etc/motd"); # Execute command without shell
The primary difference between Perl's in-built system and the "run" command is that "run"
will throw an exception on failure, and allows a list of acceptable exit values to be set.
See "Exit values" for further information.
In fact, you can even have "IPC::System::Simple" replace the default "system" function for
your package so it has the same behaviour:
use IPC::System::Simple qw(system);
system("cat *.txt"); # system now suceeds or dies!
"system" and "run" are aliases to each other.
See also "runx(), systemx() and capturex()" for variants of "system()" and "run()" that
never invoke the shell, even with a single argument.
capture()
A second subroutine, named "capture" executes a command with the same semantics as Perl's
built-in backticks (and "qx()"):
use IPC::System::Simple qw(capture);
# Capture text while invoking the shell.
my $file = capture("cat /etc/motd");
my @lines = capture("cat /etc/passwd");
However unlike regular backticks, which always use the shell, "capture" will bypass the
shell when called with multiple arguments:
# Capture text while avoiding the shell.
my $file = capture("cat", "/etc/motd");
my @lines = capture("cat", "/etc/passwd");
See also "runx(), systemx() and capturex()" for a variant of "capture()" that never
invokes the shell, even with a single argument.
runx(), systemx() and capturex()
The "runx()", "systemx()" and "capturex()" commands are identical to the multi-argument
forms of "run()", "system()" and "capture()" respectively, but never invoke the shell,
even when called with a single argument. These forms are particularly useful when a
command's argument list might be empty, for example:
systemx($cmd, @args);
The use of "systemx()" here guarantees that the shell will never be invoked, even if @args
is empty.
Exception handling
In the case where the command returns an unexpected status, both "run" and "capture" will
throw an exception, which if not caught will terminate your program with an error.
Capturing the exception is easy:
eval {
run("cat *.txt");
};
if ($@) {
print "Something went wrong - $@\n";
}
See the diagnostics section below for more details.
Exception cases
"IPC::System::Simple" considers the following to be unexpected, and worthy of exception:
· Failing to start entirely (eg, command not found, permission denied).
· Returning an exit value other than zero (but see below).
· Being killed by a signal.
· Being passed tainted data (in taint mode).
Exit values
Traditionally, system commands return a zero status for success and a non-zero status for
failure. "IPC::System::Simple" will default to throwing an exception if a non-zero exit
value is returned.
You may specify a range of values which are considered acceptable exit values by passing
an array reference as the first argument. The special constant "EXIT_ANY" can be used to
allow any exit value to be returned.
use IPC::System::Simple qw(run system capture EXIT_ANY);
run( [0..5], "cat *.txt"); # Exit values 0-5 are OK
system( [0..5], "cat *.txt"); # This works the same way
my @lines = capture( EXIT_ANY, "cat *.txt"); # Any exit is fine.
The "run" and replacement "system" subroutines returns the exit value of the process:
my $exit_value = run( [0..5], "cat *.txt");
# OR:
my $exit_value = system( [0..5] "cat *.txt");
print "Program exited with value $exit_value\n";
$EXITVAL
The exit value of any command executed by "IPC::System::Simple" can always be retrieved
from the $IPC::System::Simple::EXITVAL variable:
This is particularly useful when inspecting results from "capture", which returns the
captured text from the command.
use IPC::System::Simple qw(capture $EXITVAL EXIT_ANY);
my @enemies_defeated = capture(EXIT_ANY, "defeat_evil", "/dev/mordor");
print "Program exited with value $EXITVAL\n";
$EXITVAL will be set to "-1" if the command did not exit normally (eg, being terminated by
a signal) or did not start. In this situation an exception will also be thrown.
WINDOWS-SPECIFIC NOTES
As of "IPC::System::Simple" v0.06, the "run" subroutine when called with multiple
arguments will make available the full 32-bit exit value on Win32 systems. This is
different from the previous versions of "IPC::System::Simple" and from Perl's in-build
"system()" function, which can only handle 8-bit return values.
The "capture" subroutine always returns the 32-bit exit value under Windows. The
"capture" subroutine also never uses the shell, even when passed a single argument.
Versions of "IPC::System::Simple" before v0.09 would not search the "PATH" environment
variable when the multi-argument form of "run()" was called. Versions from v0.09 onwards
correctly search the path provided the command is provided including the extension (eg,
"notepad.exe" rather than just "notepad", or "gvim.bat" rather than just "gvim"). If no
extension is provided, ".exe" is assumed.
Signals are not supported on Windows systems. Sending a signal to a Windows process will
usually cause it to exit with the signal number used.
DIAGNOSTICS
"%s" failed to start: "%s"
The command specified did not even start. It may not exist, or you may not have
permission to use it. The reason it could not start (as determined from $!) will be
provided.
"%s" unexpectedly returned exit value %d
The command ran successfully, but returned an exit value we did not expect. The value
returned is reported.
"%s" died to signal "%s" (%d) %s
The command was killed by a signal. The name of the signal will be reported, or
"UNKNOWN" if it cannot be determined. The signal number is always reported. If we
detected that the process dumped core, then the string "and dumped core" is appended.
IPC::System::Simple::%s called with no arguments
You attempted to call "run" or "capture" but did not provide any arguments at all. At
the very lease you need to supply a command to run.
IPC::System::Simple::%s called with no command
You called "run" or "capture" with a list of acceptable exit values, but no actual
command.
IPC::System::Simple::%s called with tainted argument "%s"
You called "run" or "capture" with tainted (untrusted) arguments, which is almost
certainly a bad idea. To untaint your arguments you'll need to pass your data through
a regular expression and use the resulting match variables. See "Laundering and
Detecting Tainted Data" in perlsec for more information.
IPC::System::Simple::%s called with tainted environment $ENV{%s}
You called "run" or "capture" but part of your environment was tainted (untrusted).
You should either delete the named environment variable before calling "run", or set
it to an untainted value (usually one set inside your program). See "Cleaning Up Your
Path" in perlsec for more information.
Error in IPC::System::Simple plumbing: "%s" - "%s"
Implementing the "capture" command involves dark and terrible magicks involving pipes,
and one of them has sprung a leak. This could be due to a lack of file descriptors,
although there are other possibilities.
If you are able to reproduce this error, you are encouraged to submit a bug report
according to the "Reporting bugs" section below.
Internal error in IPC::System::Simple: "%s"
You've found a bug in "IPC::System::Simple". Please check to see if an updated
version of "IPC::System::Simple" is available. If not, please file a bug report
according to the "Reporting bugs" section below.
IPC::System::Simple::%s called with undefined command
You've passed the undefined value as a command to be executed. While this is a very
Zen-like action, it's not supported by Perl's current implementation.
DEPENDENCIES
This module depends upon Win32::Process when used on Win32 system. "Win32::Process" is
bundled as a core module in ActivePerl 5.6 and above.
There are no non-core dependencies on non-Win32 systems.
COMPARISON TO OTHER APIs
Perl provides a range of in-built functions for handling external commands, and CPAN
provides even more. The "IPC::System::Simple" differentiates itself from other options by
providing:
Extremely detailed diagnostics
The diagnostics produced by "IPC::System::Simple" are designed to provide as much
information as possible. Rather than requiring the developer to inspect $?,
"IPC::System::Simple" does the hard work for you.
If an odd exit status is provided, you're informed of what it is. If a signal kills
your process, you are informed of both its name and number. If tainted data or
environment prevents your command from running, you are informed of exactly which
datais
Exceptions on failure
"IPC::System::Simple" takes an aggressive approach to error handling. Rather than
allow commands to fail silently, exceptions are thrown when unexpected results are
seen. This allows for easy development using a try/catch style, and avoids the
possibility of accidently continuing after a failed command.
Easy access to exit status
The "run", "system" and "capture" commands all set $EXITVAL, making it easy to
determine the exit status of a command. Additionally, the "system" and "run"
interfaces return the exit status.
Consistent interfaces
When called with multiple arguments, the "run", "system" and "capture" interfaces
never invoke the shell. This differs from the in-built Perl "system" command which
may invoke the shell under Windows when called with multiple arguments. It differs
from the in-built Perl backticks operator which always invokes the shell.
BUGS
When "system" is exported, the exotic form "system { $cmd } @args" is not supported.
Attemping to use the exotic form is a syntax error. This affects the calling package
only. Use "CORE::system" if you need it, or consider using the autodie module to replace
"system" with lexical scope.
Core dumps are only checked for when a process dies due to a signal. It is not believed
there are any systems where processes can dump core without dying to a signal.
"WIFSTOPPED" status is not checked, as perl never spawns processes with the "WUNTRACED"
option.
Signals are not supported under Win32 systems, since they don't work at all like Unix
signals. Win32 singals cause commands to exit with a given exit value, which this modules
does capture.
Only 8-bit values are returned when "run()" or "system()" is called with a single value
under Win32. Multi-argument calls to "run()" and "system()", as well as the "runx()" and
"systemx()" always return the 32-bit Windows return values.
Reporting bugs
Before reporting a bug, please check to ensure you are using the most recent version of
"IPC::System::Simple". Your problem may have already been fixed in a new release.
You can find the "IPC::System::Simple" bug-tracker at
<http://rt.cpan.org/Public/Dist/Display.html?Name=IPC-System-Simple> . Please check to
see if your bug has already been reported; if in doubt, report yours anyway.
Submitting a patch and/or failing test case will greatly expedite the fixing of bugs.
FEEDBACK
If you find this module useful, please consider rating it on the CPAN Ratings service at
<http://cpanratings.perl.org/rate/?distribution=IPC-System-Simple> .
The module author loves to hear how "IPC::System::Simple" has made your life better (or
worse). Feedback can be sent to <pjf AT perltraining.au>.
SEE ALSO
autodie uses "IPC::System::Simple" to provide succeed-or-die replacements to "system" (and
other built-ins) with lexical scope.
POSIX, IPC::Run::Simple, perlipc, perlport, IPC::Run, IPC::Run3, Win32::Process
AUTHOR
Paul Fenwick <pjf AT cpan.org>
COPYRIGHT AND LICENSE
Copyright (C) 2006-2008 by Paul Fenwick
This library is free software; you can redistribute it and/or modify it under the same
terms as Perl itself, either Perl version 5.6.0 or, at your option, any later version of
Perl 5 you may have available.
perl v5.18.1 2013-10-20 IPC::System::Simple(3pm)
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