trusty (3) System::Command.3pm.gz
NAME
System::Command - Object for running system commands
VERSION
version 1.107
SYNOPSIS
use System::Command;
# invoke an external command, and return an object
$cmd = System::Command->new( @cmd );
# options can be passed as a hashref
$cmd = System::Command->new( @cmd, \%option );
# $cmd is basically a hash, with keys / accessors
$cmd->stdin(); # filehandle to the process stdin (write)
$cmd->stdout(); # filehandle to the process stdout (read)
$cmd->stderr(); # filehandle to the process stdout (read)
$cmd->pid(); # pid of the child process
# find out if the child process died
if ( $cmd->is_terminated() ) {
# the handles are not closed yet
# but $cmd->exit() et al. are available if it's dead
}
# done!
$cmd->close();
# exit information
$cmd->exit(); # exit status
$cmd->signal(); # signal
$cmd->core(); # core dumped? (boolean)
# cut to the chase
my ( $pid, $in, $out, $err ) = System::Command->spawn(@cmd);
DESCRIPTION
"System::Command" is a class that launches external system commands and return an object representing
them, allowing to interact with them through their "STDIN", "STDOUT" and "STDERR" handles.
METHODS
"System::Command" supports the following methods:
new( @cmd )
Runs an external command using the list in @cmd.
If @cmd contains a hash reference, it is taken as an option hash.
If several option hashes are passed to "new()", they will be merged together with individual values being
overridden by those (with the same key) from hashes that appear later in the list.
To allow subclasses to support their own set of options, unrecognized options are silently ignored.
The recognized keys are:
"cwd"
The current working directory in which the command will be run.
"env"
A hashref containing key / values to add to the command environment.
If several option hashes define the "env" key, the hashes they point to will be merged into one
(instead of the last one taking precedence).
If a value is "undef", the variable corresponding to the key will be removed from the environment.
"input"
A string that is send to the command's standard input, which is then closed.
Using the empty string as "input" will close the command's standard input without writing to it.
Using "undef" as "input" will not do anything. This behaviour provides a way to modify previous
options populated by some other part of the program.
On some systems, some commands may close standard input on startup, which will cause a SIGPIPE when
trying to write to it. This will raise an exception.
The "System::Command" object returned by "new()" has a number of attributes defined (see below).
close()
Close all pipes to the child process, collects exit status, etc. and defines a number of attributes (see
below).
is_terminated()
Returns a true value if the underlying process was terminated.
If the process was indeed terminated, collects exit status, etc. and defines the same attributes as
"close()", but does not close all pipes to the child process.
spawn( @cmd )
This shortcut method calls "new()" (and so accepts options in the same manner) and directly returns the
"pid", "stdin", "stdout" and "stderr" attributes, in that order.
Accessors
The attributes of a "System::Command" object are also accessible through a number of accessors.
The object returned by "new()" will have the following attributes defined:
cmdline()
Return the command-line actually executed, as a list of strings.
options()
The merged list of options used to run the command.
pid()
The PID of the underlying command.
stdin()
A filehandle opened in write mode to the child process' standard input.
stdout()
A filehandle opened in read mode to the child process' standard output.
stderr()
A filehandle opened in read mode to the child process' standard error output.
Regarding the handles to the child process, note that in the following code:
my $fh = System::Command->new( @cmd )->stdout;
$fh is opened and points to the output handle of the child process, while the anonymous "System::Command"
object has been destroyed. Once $fh is destroyed, the subprocess will be reaped, thus avoiding zombies.
After the call to "close()" or after "is_terminated()" returns true, the following attributes will be
defined:
exit()
The exit status of the underlying command.
core()
A boolean value indicating if the command dumped core.
signal()
The signal, if any, that killed the command.
CAVEAT EMPTOR
Note that "System::Command" uses "waitpid()" to catch the status information of the child processes it
starts. This means that if your code (or any module you "use") does something like the following:
local $SIG{CHLD} = 'IGNORE'; # reap child processes
"System::Command" will not be able to capture the "exit", "core" and "signal" attributes. It will instead
set all of them to the impossible value "-1", and display the warning "Child process already reaped,
check for a SIGCHLD handler".
To silence this warning (and accept the impossible status information), load "System::Command" with:
use System::Command -quiet;
It is also possible to more finely control the warning by setting the $System::Command::QUIET variable
(the warning is not emitted if the variable is set to a true value).
If the subprocess started by "System::Command" has a short life expectancy, and no other child process is
expected to die during that time, you could even disable the handler locally (use at your own risks):
{
local $SIG{CHLD};
my $cmd = System::Command->new(@cmd);
...
}
AUTHOR
Philippe Bruhat (BooK), "<book at cpan.org>"
ACKNOWLEDGEMENTS
Thanks to Alexis Sukrieh (SUKRIA) who, when he saw the description of "Git::Repository::Command" during
my talk at OSDC.fr 2010, asked why it was not an independent module. This module was started by taking
out of "Git::Repository::Command" 1.08 the parts that weren't related to Git.
Thanks to Christian Walde (MITHALDU) for his help in making this module work better under Win32.
The System::Command::Reaper class was added after the addition of Git::Repository::Command::Reaper in
Git::Repository::Command 1.11. It was later removed from System::Command version 1.03, and brought back
from the dead to deal with the zombie apocalypse in version 1.106.
BUGS
Please report any bugs or feature requests to "bug-system-command at rt.cpan.org", or through the web
interface at <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=System-Command>. I will be notified, and
then you'll automatically be notified of progress on your bug as I make changes.
SUPPORT
You can find documentation for this module with the perldoc command.
perldoc System::Command
You can also look for information at:
• RT: CPAN's request tracker
<http://rt.cpan.org/NoAuth/Bugs.html?Dist=System-Command>
• AnnoCPAN: Annotated CPAN documentation
<http://annocpan.org/dist/System-Command>
• CPAN Ratings
<http://cpanratings.perl.org/d/System-Command>
• Search CPAN
<http://search.cpan.org/dist/System-Command/>
COPYRIGHT
Copyright 2010-2013 Philippe Bruhat (BooK).
LICENSE
This program is free software; you can redistribute it and/or modify it under the terms of either: the
GNU General Public License as published by the Free Software Foundation; or the Artistic License.
See <http://dev.perl.org/licenses/> for more information.