#!/usr/bin/perl -w

use strict;
use Data::Dumper;

# execute command without capturing STDERR
sub exec_nocap {
	# execute command via backticks, getting output (STDOUT) and return value
	my $command = shift;
	my $out = `$command`;
	my $return = $?;
	
	# dump everything (in an anonymous hash)
	print Dumper {
		'Return value' => $return,
		'STDOUT' => $out,
	};
}

# execute command, capturing STDERR
sub exec_cap {
	# dupe STDERR, to be restored later
	open(my $stderr, ">&", \*STDERR) or do { print "Can't dupe STDERR: $!\n"; exit; };
	
	# close first (according to the perldocs)
	close(STDERR) or die "Can't close STDERR: $!\n";
	
	# redirect STDERR to in-memory scalar
	my $err;
	open(STDERR, '>', \$err) or do { print "Can't redirect STDERR: $!\n"; exit; };
	
	# just to demonstrate that STDERR capturing is working
	warn('this is a warning');
	
	# execute command via backticks, getting output (STDOUT) and return value
	my $command = shift;
	my $out = `$command`;
	my $return = $?;
  
  # restore original STDERR
  open(STDERR, ">&", $stderr) or do { print "Can't restore STDERR: $!\n"; exit; };
  
  print Dumper({
    'Return value' => $return,
    'STDOUT' => $out,
    'Redirected STDERR' => $err,
  });
}

exec_nocap('perl -e "die(\'this is a fatal error\')"');

print "\n"x5;

exec_cap('perl -e "die(\'this is a fatal error\')"');