How to get return value from call to perl sub from bash script?

Question

I am calling a perl script from a bash script. I want to obtain the return value that the perl script returns in the bash script in order to act on it. When I have the following, the output is a blank line to the console when I expect it to be "good".

bashThing.sh

#!/bin/bash

ARG="valid"
VAL=$(perl -I. -MperlThing -e "perlThing::isValid ${ARG}")
echo $VAL

perlThing.pm

#! /usr/bin/perl -w
use strict;

package perlThing;

sub isValid
{
  my $arg = shift;
  if($arg == "valid")
  {
    return "good";
  }
  else
  {
    return "bad";
  }
}

1;

toolic · Accepted Answer · 2020-05-29 16:52:13Z

2

You didn't have Perl warnings enabled completely. You would have seen several warnings. I enabled warnings both in bash (using -w on the Perl one-liner), and in Perl with use warnings;. The shebang line is ignored in the .pm file since it is not being executed as a script.

isValid returned a string, but you were ignoring the returned value. To fix that, use print in the one-liner.

You also needed to pass the value to isValid properly.

Lastly, you need to use eq instead of == for string comparison.

bash:

#!/bin/bash

ARG="valid"
VAL=$(perl -w -I. -MperlThing -e "print perlThing::isValid(q(${ARG}))")
echo $VAL

Perl:

use strict;
use warnings;

package perlThing;

sub isValid
{
  my $arg = shift;
  if($arg eq "valid")
  {
    return "good";
  }
  else
  {
    return "bad";
  }
}

1;

edited May 29, 2020 at 16:52

answered May 29, 2020 at 16:45

toolic

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Comments

pii_ke · Accepted Answer · 2020-05-29 17:19:36Z

1

If you expect the value good or bad in $VAR, then you should print them not return them.

Other than printed stuff, the perl process can pass only integer return values to calling program. And you can check that using $? in bash script, this variable stores the return value of last run process.

edited May 29, 2020 at 17:19

answered May 29, 2020 at 17:01

pii_ke

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1 Comment

Fabio says Reinstate Monica Over a year ago

The Bash variable that stores the return code should be $?, not $@. Can you please check?

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