package IPC::System::Simple;

# ABSTRACT: Run commands simply, with detailed diagnostics

use 5.006;
use strict;
use warnings;
use re 'taint';
use Carp;
use List::Util qw(first);
use Scalar::Util qw(tainted);
use Config;
use constant WINDOWS => ($^O eq 'MSWin32');
use constant VMS     => ($^O eq 'VMS');

BEGIN {

    # It would be lovely to use the 'if' module here, but it didn't
    # enter core until 5.6.2, and we want to keep 5.6.0 compatibility.


    if (WINDOWS) {

        ## no critic (ProhibitStringyEval)

        eval q{
            use Win32::Process qw(INFINITE NORMAL_PRIORITY_CLASS);
            use File::Spec;
            use Win32;
            use Win32::ShellQuote;

            # This uses the same rules as the core win32.c/get_shell() call.
            use constant WINDOWS_SHELL => eval { Win32::IsWinNT() }
                ? [ File::Spec->catfile(Win32::GetFolderPath(Win32::CSIDL_SYSTEM), 'cmd.exe'), '/x/d/c' ]
                : [ File::Spec->catfile(Win32::GetFolderPath(Win32::CSIDL_SYSTEM), 'command.com'), '/c' ];

            # These are used when invoking _win32_capture
            use constant NO_SHELL  => 0;
            use constant USE_SHELL => 1;

        };

        ## use critic

        # Die nosily if any of the above broke.
        die $@ if $@;
    }
}

# Note that we don't use WIFSTOPPED because perl never uses
# the WUNTRACED flag, and hence will never return early from
# system() if the child processes is suspended with a SIGSTOP.

use POSIX qw(WIFEXITED WEXITSTATUS WIFSIGNALED WTERMSIG);

use constant FAIL_START     => q{"%s" failed to start: "%s"};
use constant FAIL_PLUMBING  => q{Error in IPC::System::Simple plumbing: "%s" - "%s"};
use constant FAIL_CMD_BLANK => q{Entirely blank command passed: "%s"};
use constant FAIL_INTERNAL  => q{Internal error in IPC::System::Simple: "%s"};
use constant FAIL_TAINT     => q{%s called with tainted argument "%s"};
use constant FAIL_TAINT_ENV => q{%s called with tainted environment $ENV{%s}};
use constant FAIL_SIGNAL    => q{"%s" died to signal "%s" (%d)%s};
use constant FAIL_BADEXIT   => q{"%s" unexpectedly returned exit value %d};

use constant FAIL_UNDEF     => q{%s called with undefined command};


use constant FAIL_POSIX     => q{IPC::System::Simple does not understand the POSIX error '%s'.  Please check https://metacpan.org/pod/IPC::System::Simple to see if there is an updated version.  If not please report this as a bug to https://github.com/pjf/ipc-system-simple/issues};

# On Perl's older than 5.8.x we can't assume that there'll be a
# $^{TAINT} for us to check, so we assume that our args may always
# be tainted.
use constant ASSUME_TAINTED => ($] < 5.008);

use constant EXIT_ANY_CONST => -1;			# Used internally
use constant EXIT_ANY       => [ EXIT_ANY_CONST ];	# Exported

use constant UNDEFINED_POSIX_RE => qr{not (?:defined|a valid) POSIX macro|not implemented on this architecture};

require Exporter;
our @ISA = qw(Exporter);

our @EXPORT_OK = qw( 
    capture  capturex
    run      runx
    system   systemx
    $EXITVAL EXIT_ANY
);

our $VERSION = '1.30';
$VERSION =~ tr/_//d;

our $EXITVAL = -1;

my @Signal_from_number = split(' ', $Config{sig_name});

# Environment variables we don't want to see tainted.
my @Check_tainted_env = qw(PATH IFS CDPATH ENV BASH_ENV);
if (WINDOWS) {
	push(@Check_tainted_env, 'PERL5SHELL');
}
if (VMS) {
	push(@Check_tainted_env, 'DCL$PATH');
}

# Not all systems implement the WIFEXITED calls, but POSIX
# will always export them (even if they're just stubs that
# die with an error).  Test for the presence of a working
# WIFEXITED and friends, or define our own.

eval { WIFEXITED(0); };

if ($@ =~ UNDEFINED_POSIX_RE) {
        no warnings 'redefine';  ## no critic
	*WIFEXITED   = sub { not $_[0] & 0xff };
	*WEXITSTATUS = sub { $_[0] >> 8  };
	*WIFSIGNALED = sub { $_[0] & 127 };
	*WTERMSIG    = sub { $_[0] & 127 };
} elsif ($@) {
	croak sprintf FAIL_POSIX, $@;
}

# None of the POSIX modules I've found define WCOREDUMP, although
# many systems define it.  Check the POSIX module in the hope that
# it may actually be there.


# TODO: Ideally, $NATIVE_WCOREDUMP should be a constant.

my $NATIVE_WCOREDUMP;

eval { POSIX::WCOREDUMP(1); };

if ($@ =~ UNDEFINED_POSIX_RE) {
	*WCOREDUMP = sub { $_[0] & 128 };
        $NATIVE_WCOREDUMP = 0;
} elsif ($@) {
	croak sprintf FAIL_POSIX, $@;
} else {
	# POSIX actually has it defined!  Huzzah!
	*WCOREDUMP = \&POSIX::WCOREDUMP;
        $NATIVE_WCOREDUMP = 1;
}

sub _native_wcoredump {
    return $NATIVE_WCOREDUMP;
}

# system simply calls run

no warnings 'once'; ## no critic
*system  = \&run;
*systemx = \&runx;
use warnings;

# run is our way of running a process with system() semantics

sub run {

	_check_taint(@_);

	my ($valid_returns, $command, @args) = _process_args(@_);

        # If we have arguments, we really want to call systemx,
        # so we do so.

	if (@args) {
                return systemx($valid_returns, $command, @args);
	}

    if (WINDOWS) {
        my $pid = _spawn_or_die(&WINDOWS_SHELL->[0], join ' ', @{&WINDOWS_SHELL}, $command);
        $pid->Wait(INFINITE);	# Wait for process exit.
        $pid->GetExitCode($EXITVAL);
        return _check_exit($command,$EXITVAL,$valid_returns);
    }

    # Without arguments, we're calling system, and checking
        # the results.

	# We're throwing our own exception on command not found, so
	# we don't need a warning from Perl.

        {
            # silence 'Statement unlikely to be reached' warning
            no warnings 'exec';             ## no critic
            CORE::system($command,@args);
        }

	return _process_child_error($?,$command,$valid_returns);
}

# runx is just like system/run, but *never* invokes the shell.

sub runx {
    _check_taint(@_);

    my ($valid_returns, $command, @args) = _process_args(@_);

    if (WINDOWS) {
        our $EXITVAL = -1;

        my $pid = _spawn_or_die($command, Win32::ShellQuote::quote_native($command, @args));

        $pid->Wait(INFINITE);	# Wait for process exit.
        $pid->GetExitCode($EXITVAL);
        return _check_exit($command,$EXITVAL,$valid_returns);
    }

    # If system() fails, we throw our own exception.  We don't
    # need to have perl complain about it too.

    no warnings; ## no critic

    CORE::system { $command } $command, @args;

    return _process_child_error($?, $command, $valid_returns);
}

# capture is our way of running a process with backticks/qx semantics

sub capture {
	_check_taint(@_);

	my ($valid_returns, $command, @args) = _process_args(@_);

        if (@args) {
            return capturex($valid_returns, $command, @args);
        }

        if (WINDOWS) {
            # USE_SHELL really means "You may use the shell if you need it."
            return _win32_capture(USE_SHELL, $valid_returns, $command);
        }

	our $EXITVAL = -1;

	my $wantarray = wantarray();

	# We'll produce our own warnings on failure to execute.
	no warnings 'exec';	## no critic

        if ($wantarray) {
                my @results = qx($command);
                _process_child_error($?,$command,$valid_returns);
                return @results;
        } 

        my $results = qx($command);
        _process_child_error($?,$command,$valid_returns);
        return $results;
}

# _win32_capture implements the capture and capurex commands on Win32.
# We need to wrap the whole internals of this sub into
# an if (WINDOWS) block to avoid it being compiled on non-Win32 systems.

sub _win32_capture {
    if (not WINDOWS) {
        croak sprintf(FAIL_INTERNAL, "_win32_capture called when not under Win32");
    } else {

        my ($use_shell, $valid_returns, $command, @args) = @_;

        my $wantarray = wantarray();

        # Perl doesn't support multi-arg open under
        # Windows.  Perl also doesn't provide very good
        # feedback when normal backtails fail, either;
        # it returns exit status from the shell
        # (which is indistinguishable from the command
        # running and producing the same exit status).

        # As such, we essentially have to write our own
        # backticks.

        # We start by dup'ing STDOUT.

        open(my $saved_stdout, '>&', \*STDOUT)  ## no critic
                or croak sprintf(FAIL_PLUMBING, "Can't dup STDOUT", $!);

        # We now open up a pipe that will allow us to	
        # communicate with the new process.

        pipe(my ($read_fh, $write_fh))
                or croak sprintf(FAIL_PLUMBING, "Can't create pipe", $!);

        # Allow CRLF sequences to become "\n", since
        # this is what Perl backticks do.

        binmode($read_fh, ':crlf');

        # Now we re-open our STDOUT to $write_fh...

        open(STDOUT, '>&', $write_fh)  ## no critic
                or croak sprintf(FAIL_PLUMBING, "Can't redirect STDOUT", $!);

        # If we have args, or we're told not to use the shell, then
        # we treat $command as our shell.  Otherwise we grub around
        # in our command to look for a command to run.
        #
        # Note that we don't actually *use* the shell (although in
        # a future version we might).  Being told not to use the shell
        # (capturex) means we treat our command as really being a command,
        # and not a command line.

        my $exe =   @args                      ? $command :
                    (! $use_shell)             ? $command :
                    $command =~ m{^"([^"]+)"}x ? $1       :
                    $command =~ m{(\S+)     }x ? $1       :
                    croak sprintf(FAIL_CMD_BLANK, $command);

        # And now we spawn our new process with inherited
        # filehandles.

        my $err;
        my $pid = eval { 
                _spawn_or_die($exe, @args ? Win32::ShellQuote::quote_native($command, @args) : $command);
        }
        or do {
                $err = $@;
        };

        # Regardless of whether our command ran, we must restore STDOUT.
        # RT #48319
        open(STDOUT, '>&', $saved_stdout)  ## no critic
                or croak sprintf(FAIL_PLUMBING,"Can't restore STDOUT", $!);

        # And now, if there was an actual error , propagate it.
        die $err if defined $err;   # If there's an error from _spawn_or_die

        # Clean-up the filehandles we no longer need...

        close($write_fh)
                or croak sprintf(FAIL_PLUMBING,q{Can't close write end of pipe}, $!);
        close($saved_stdout)
                or croak sprintf(FAIL_PLUMBING,q{Can't close saved STDOUT}, $!);

        # Read the data from our child...

        my (@results, $result);

        if ($wantarray) {
                @results = <$read_fh>;
        } else {
                $result = join("",<$read_fh>);
        }

        # Tidy up our windows process and we're done!

        $pid->Wait(INFINITE);	# Wait for process exit.
        $pid->GetExitCode($EXITVAL);

        _check_exit($command,$EXITVAL,$valid_returns);

        return $wantarray ? @results : $result;

    }
}

# capturex() is just like backticks/qx, but never invokes the shell.

sub capturex {
	_check_taint(@_);

	my ($valid_returns, $command, @args) = _process_args(@_);

	our $EXITVAL = -1;

	my $wantarray = wantarray();

	if (WINDOWS) {
            return _win32_capture(NO_SHELL, $valid_returns, $command, @args);
        }

	# We can't use a multi-arg piped open here, since 5.6.x
	# doesn't like them.  Instead we emulate what 5.8.x does,
	# which is to create a pipe(), set the close-on-exec flag
	# on the child, and the fork/exec.  If the exec fails, the
	# child writes to the pipe.  If the exec succeeds, then
	# the pipe closes without data.

	pipe(my ($read_fh, $write_fh))
		or croak sprintf(FAIL_PLUMBING, "Can't create pipe", $!);

	# This next line also does an implicit fork.
	my $pid = open(my $pipe, '-|');	 ## no critic

	if (not defined $pid) {
		croak sprintf(FAIL_START, $command, $!);
	} elsif (not $pid) {
		# Child process, execs command.

		close($read_fh);

		# TODO: 'no warnings exec' doesn't get rid
		# of the 'unlikely to be reached' warnings.
		# This is a bug in perl / perldiag / perllexwarn / warnings.

		no warnings;   ## no critic

		CORE::exec { $command } $command, @args;

		# Oh no, exec fails!  Send the reason why to
		# the parent.

		print {$write_fh} int($!);
		exit(-1);
	}

	{
		# In parent process.

		close($write_fh);

		# Parent process, check for child error.
		my $error = <$read_fh>;

		# Tidy up our pipes.
		close($read_fh);

		# Check for error.
		if ($error) {
			# Setting $! to our child error number gives
			# us nice looking strings when printed.
			local $! = $error;
			croak sprintf(FAIL_START, $command, $!);
		}
	}

	# Parent process, we don't care about our pid, but we
	# do go and read our pipe.

	if ($wantarray) {
		my @results = <$pipe>;
		close($pipe);
		_process_child_error($?,$command,$valid_returns);
		return @results;
	}

	# NB: We don't check the return status on close(), since
	# on failure it sets $?, which we then inspect for more
	# useful information.

	my $results = join("",<$pipe>);
	close($pipe);
	_process_child_error($?,$command,$valid_returns);
	
	return $results;

}

# Tries really hard to spawn a process under Windows.  Returns
# the pid on success, or undef on error.

sub _spawn_or_die {

	# We need to wrap practically the entire sub in an
	# if block to ensure it doesn't get compiled under non-Win32
	# systems.  Compiling on these systems would not only be a
	# waste of time, but also results in complaints about
	# the NORMAL_PRIORITY_CLASS constant.

	if (not WINDOWS) {
		croak sprintf(FAIL_INTERNAL, "_spawn_or_die called when not under Win32");
	} else {
		my ($orig_exe, $cmdline) = @_;
		my $pid;

		my $exe = $orig_exe;

		# If our command doesn't have an extension, add one.
		$exe .= $Config{_exe} if ($exe !~ m{\.});

		Win32::Process::Create(
			$pid, $exe, $cmdline, 1, NORMAL_PRIORITY_CLASS, "."
		) and return $pid;

		my @path = split(/;/,$ENV{PATH});

		foreach my $dir (@path) {
			my $fullpath = File::Spec->catfile($dir,$exe);

			# We're using -x here on the assumption that stat()
			# is faster than spawn, so trying to spawn a process
			# for each path element will be unacceptably
			# inefficient.

			if (-x $fullpath) {
				Win32::Process::Create(
					$pid, $fullpath, $cmdline, 1,
					NORMAL_PRIORITY_CLASS, "."
				) and return $pid;
			}
		}

		croak sprintf(FAIL_START, $orig_exe, $^E);
	}
}

# Complain on tainted arguments or environment.
# ASSUME_TAINTED is true for 5.6.x, since it's missing ${^TAINT}

sub _check_taint {
	return if not (ASSUME_TAINTED or ${^TAINT});
	my $caller = (caller(1))[3];
	foreach my $var (@_) {
		if (tainted $var) {
			croak sprintf(FAIL_TAINT, $caller, $var);
		}
	}
	foreach my $var (@Check_tainted_env) {
		if (tainted $ENV{$var} ) {
			croak sprintf(FAIL_TAINT_ENV, $caller, $var);
		}
	}

	return;

}

# This subroutine performs the difficult task of interpreting
# $?.  It's not intended to be called directly, as it will
# croak on errors, and its implementation and interface may
# change in the future.

sub _process_child_error {
	my ($child_error, $command, $valid_returns) = @_;
	
	$EXITVAL = -1;

	my $coredump = WCOREDUMP($child_error);

        # There's a bug in perl 5.8.9 and 5.10.0 where if the system
        # does not provide a native WCOREDUMP, then $? will
        # never contain coredump information.  This code
        # checks to see if we have the bug, and works around
        # it if needed.

        if ($] >= 5.008009 and not $NATIVE_WCOREDUMP) {
            $coredump ||= WCOREDUMP( ${^CHILD_ERROR_NATIVE} );
        }

	if ($child_error == -1) {
		croak sprintf(FAIL_START, $command, $!);

	} elsif ( WIFEXITED( $child_error ) ) {
		$EXITVAL = WEXITSTATUS( $child_error );

		return _check_exit($command,$EXITVAL,$valid_returns);

	} elsif ( WIFSIGNALED( $child_error ) ) {
		my $signal_no   = WTERMSIG( $child_error );
		my $signal_name = $Signal_from_number[$signal_no] || "UNKNOWN";

		croak sprintf FAIL_SIGNAL, $command, $signal_name, $signal_no, ($coredump ? " and dumped core" : "");


	} 

	croak sprintf(FAIL_INTERNAL, qq{'$command' ran without exit value or signal});

}

# A simple subroutine for checking exit values.  Results in better
# assurance of consistent error messages, and better forward support
# for new features in I::S::S.

sub _check_exit {
	my ($command, $exitval, $valid_returns) = @_;

	# If we have a single-value list consisting of the EXIT_ANY
	# value, then we're happy with whatever exit value we're given.
	if (@$valid_returns == 1 and $valid_returns->[0] == EXIT_ANY_CONST) {
		return $exitval;
	}

	if (not defined first { $_ == $exitval } @$valid_returns) {
		croak sprintf FAIL_BADEXIT, $command, $exitval;
	}	
	return $exitval;
}


# This subroutine simply determines a list of valid returns, the command
# name, and any arguments that we need to pass to it.

sub _process_args {
	my $valid_returns = [ 0 ];
	my $caller = (caller(1))[3];

	if (not @_) {
		croak "$caller called with no arguments";
	}

	if (ref $_[0] eq "ARRAY") {
		$valid_returns = shift(@_);
	}

	if (not @_) {
		croak "$caller called with no command";
	}

	my $command = shift(@_);

        if (not defined $command) {
                croak sprintf( FAIL_UNDEF, $caller );
        }

	return ($valid_returns,$command,@_);

}

1;

__END__

=head1 NAME

IPC::System::Simple - Run commands simply, with detailed diagnostics

=head1 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);

=head1 DESCRIPTION

Calling Perl's in-built C<system()> function is easy, 
determining if it was successful is I<hard>.  Let's face it,
C<$?> isn't the nicest variable in the world to play with, and
even if you I<do> check it, producing a well-formatted error
string takes a lot of work.

C<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 C<system> commands will either succeed (run to
completion and return a zero exit value), or die with rich diagnostic
messages.

The C<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 L</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 C<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!

=head1 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);

=head1 ADVANCED USAGE

=head2 run() and system()

C<IPC::System::Simple> provides a subroutine called
C<run>, that executes a command using the same semantics as
Perl's built-in C<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 C<run> command is that C<run> will throw an exception on
failure, and allows a list of acceptable exit values to be set.
See L</Exit values> for further information.

In fact, you can even have C<IPC::System::Simple> replace the
default C<system> function for your package so it has the
same behaviour:

    use IPC::System::Simple qw(system);

    system("cat *.txt");  # system now succeeds or dies!

C<system> and C<run> are aliases to each other.

See also L</runx(), systemx() and capturex()> for variants of
C<system()> and C<run()> that never invoke the shell, even with
a single argument.

=head2 capture()

A second subroutine, named C<capture> executes a command with
the same semantics as Perl's built-in backticks (and C<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, C<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 L</runx(), systemx() and capturex()> for a variant of
C<capture()> that never invokes the shell, even with a single
argument.

=head2 runx(), systemx() and capturex()

The C<runx()>, C<systemx()> and C<capturex()> commands are identical
to the multi-argument forms of C<run()>, C<system()> and C<capture()>
respectively, but I<never> invoke the shell, even when called with a
single argument.  These forms are particularly useful when a command's
argument list I<might> be empty, for example:

    systemx($cmd, @args);

The use of C<systemx()> here guarantees that the shell will I<never>
be invoked, even if C<@args> is empty.

=head2 Exception handling

In the case where the command returns an unexpected status, both C<run> and
C<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.

=head3 Exception cases

C<IPC::System::Simple> considers the following to be unexpected,
and worthy of exception:

=over 4

=item *

Failing to start entirely (eg, command not found, permission denied).

=item *

Returning an exit value other than zero (but see below).

=item *

Being killed by a signal.

=item *

Being passed tainted data (in taint mode).

=back

=head2 Exit values

Traditionally, system commands return a zero status for success and a
non-zero status for failure.  C<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 I<array reference> as the first argument.  The
special constant C<EXIT_ANY> can be used to allow I<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 C<run> and replacement C<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";

=head3 $EXITVAL

The exit value of any command executed by C<IPC::System::Simple>
can always be retrieved from the C<$IPC::System::Simple::EXITVAL>
variable:

This is particularly useful when inspecting results from C<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";

C<$EXITVAL> will be set to C<-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.

=head2 WINDOWS-SPECIFIC NOTES

The C<run> subroutine make available the full 32-bit exit value on
Win32 systems. This has been true since C<IPC::System::Simple> v0.06
when called with multiple arguments, and since v1.25 when called with
a single argument.  This is different from the previous versions of
C<IPC::System::Simple> and from Perl's in-build C<system()> function,
which can only handle 8-bit return values.

The C<capture> subroutine always returns the 32-bit exit value under
Windows.  The C<capture> subroutine also never uses the shell,
even when passed a single argument.

The C<run> subroutine always uses a shell when passed a single
argument. On NT systems, it uses C<cmd.exe> in the system root, and on
non-NT systems it uses C<command.com> in the system root.

As of C<IPC::System::Simple> v1.25, the C<runx> and C<capturex>
subroutines, as well as multiple-argument calls to the C<run> and
C<capture> subroutines, have their arguments properly quoted, so that
arugments with spaces and the like work properly. Unfortunately, this
breaks any attempt to invoke the shell itself. If you really need to
execute C<cmd.exe> or C<command.com>, use the single-argument form.
For single-argument calls to C<run> and C<capture>, the argument must
be properly shell-quoted in advance of the call.

Versions of C<IPC::System::Simple> before v0.09 would not search
the C<PATH> environment variable when the multi-argument form of
C<run()> was called.  Versions from v0.09 onwards correctly search
the path provided the command is provided including the extension
(eg, C<notepad.exe> rather than just C<notepad>, or C<gvim.bat> rather
than just C<gvim>).  If no extension is provided, C<.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.

=head1 DIAGNOSTICS

=over 4

=item "%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 C<$!>) will be provided.

=item "%s" unexpectedly returned exit value %d

The command ran successfully, but returned an exit value we did
not expect.  The value returned is reported.

=item "%s" died to signal "%s" (%d) %s

The command was killed by a signal.  The name of the signal
will be reported, or C<UNKNOWN> if it cannot be determined.  The
signal number is always reported.  If we detected that the
process dumped core, then the string C<and dumped core> is
appended.

=item IPC::System::Simple::%s called with no arguments

You attempted to call C<run> or C<capture> but did not provide any
arguments at all.  At the very lease you need to supply a command
to run.

=item IPC::System::Simple::%s called with no command

You called C<run> or C<capture> with a list of acceptable exit values,
but no actual command.

=item IPC::System::Simple::%s called with tainted argument "%s"

You called C<run> or C<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 L<perlsec/Laundering and Detecting Tainted Data> for more information.

=item IPC::System::Simple::%s called with tainted environment $ENV{%s}

You called C<run> or C<capture> but part of your environment was tainted
(untrusted).  You should either delete the named environment
variable before calling C<run>, or set it to an untainted value
(usually one set inside your program).  See
L<perlsec/Cleaning Up Your Path> for more information.

=item Error in IPC::System::Simple plumbing: "%s" - "%s"

Implementing the C<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 L</Reporting bugs> section below.

=item Internal error in IPC::System::Simple: "%s"

You've found a bug in C<IPC::System::Simple>.  Please check to
see if an updated version of C<IPC::System::Simple> is available.
If not, please file a bug report according to the L</Reporting bugs> section
below.

=item 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.

=back

=head1 DEPENDENCIES

This module depends upon L<Win32::Process> when used on Win32
system.  C<Win32::Process> is bundled as a core module in ActivePerl 5.6
and above.

There are no non-core dependencies on non-Win32 systems.

=head1 COMPARISON TO OTHER APIs

Perl provides a range of in-built functions for handling external
commands, and CPAN provides even more.  The C<IPC::System::Simple>
differentiates itself from other options by providing:

=over 4

=item Extremely detailed diagnostics

The diagnostics produced by C<IPC::System::Simple> are designed
to provide as much information as possible.  Rather than requiring
the developer to inspect C<$?>, C<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 data or environmental variable is
tainted.

=item Exceptions on failure

C<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 accidentally
continuing after a failed command.

=item Easy access to exit status

The C<run>, C<system> and C<capture> commands all set C<$EXITVAL>,
making it easy to determine the exit status of a command.
Additionally, the C<system> and C<run> interfaces return the exit
status.

=item Consistent interfaces

When called with multiple arguments, the C<run>, C<system> and
C<capture> interfaces I<never> invoke the shell.  This differs
from the in-built Perl C<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.

=back

=head1 BUGS

When C<system> is exported, the exotic form C<system { $cmd } @args>
is not supported.  Attemping to use the exotic form is a syntax
error.  This affects the calling package I<only>.  Use C<CORE::system>
if you need it, or consider using the L<autodie> module to replace
C<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.

C<WIFSTOPPED> status is not checked, as perl never spawns processes
with the C<WUNTRACED> option.

Signals are not supported under Win32 systems, since they don't
work at all like Unix signals.  Win32 signals cause commands to
exit with a given exit value, which this modules I<does> capture.

=head2 Reporting bugs

Before reporting a bug, please check to ensure you are using the
most recent version of C<IPC::System::Simple>.  Your problem may
have already been fixed in a new release.

You can find the C<IPC::System::Simple> bug-tracker at
L<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.

=head1 FEEDBACK

If you find this module useful, please consider rating it on the
CPAN Ratings service at
L<http://cpanratings.perl.org/rate/?distribution=IPC-System-Simple> .

The module author loves to hear how C<IPC::System::Simple> has made
your life better (or worse).  Feedback can be sent to
E<lt>pjf@perltraining.com.auE<gt>.

=head1 SEE ALSO

L<autodie> uses C<IPC::System::Simple> to provide succeed-or-die
replacements to C<system> (and other built-ins) with lexical scope.

L<POSIX>, L<IPC::Run::Simple>, L<perlipc>, L<perlport>, L<IPC::Run>,
L<IPC::Run3>, L<Win32::Process>

=head1 AUTHOR

Paul Fenwick E<lt>pjf@cpan.orgE<gt>

=head1 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.

=for Pod::Coverage WCOREDUMP

=cut