Capture return code of Perl system command with redirection

Question

I am trying to capture the return code of a system call. To make it simple, consider a command that you know returns code 1, for example the following bash script t.sh:

#! /bin/bash
exit 1

Then consider:

use warnings;
use strict;
use feature qw(say);

my $res=system("t.sh");
say ($?>>8);

$res=system("t.sh &>/dev/null");
say ($?>>8);

which prints

1
0

Why does the second system call (the one with error redirection) give me a zero return code?

"&>" should be "2>". You are running the command in background, and gets the 0 exit code — Miguel Prz
– Miguel Prz, Commented Aug 14, 2014 at 7:08
Thanks, but I am trying to redirect both standard output and standard error.. See gnu.org/software/bash/manual/html_node/Redirections.html. According to that page, the syntax should be &> ? — Håkon Hægland
– Håkon Hægland, Commented Aug 14, 2014 at 7:13
Thanks @Miller, this works! (It would be nice to know why &> is not working though, since it is given in the manual) — Håkon Hægland
– Håkon Hægland, Commented Aug 14, 2014 at 7:19
@HåkonHægland &> is a relatively new Bash feature (introduced in v4.x). Check your version with bash --version; &> works properly on my system with v4.1.2. &> is semantically equivalent to >word 2>&1, so you could do system('t.sh > /dev/null 2>&1');. Note the & in 2>&1; if you leave this off, you will create a file named 1 in the current directory. — ThisSuitIsBlackNot
– ThisSuitIsBlackNot, Commented Aug 14, 2014 at 14:30

ThisSuitIsBlackNot · Accepted Answer · 2014-08-15 15:36:12Z

1

I can't duplicate your issue with Bash v4.1.2:

$ perl -wE 'system( q{/bin/bash -c "true &> /dev/null"} ); say $? >> 8'
0
$ perl -wE 'system( q{/bin/bash -c "false &> /dev/null"} ); say $? >> 8'
1

However, the &> redirection operator is not portable and should generally be avoided. I'm not sure, but it seems like it may not have worked properly in earlier releases.^*

The following syntax is semantically equivalent and much more portable:

>file 2>&1

(note the & in 2>&1)

Use it instead.

* According to the Advanced Bash Scripting Guide, "This operator is now functional, as of Bash 4, final release."

answered Aug 15, 2014 at 15:36

ThisSuitIsBlackNot

24.2k9 gold badges66 silver badges111 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Capture return code of Perl system command with redirection

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related