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J. Doe
Asked: 2018-06-22 10:07:00 +0800 CST

How do I carry my variables from a Bash script into a Perl one?

  • 772

I have variables in a bash script that I need to be carried over into a perl one. I have the variables $gal and $obsid declared in the bash script, and then I call the new program.

gal=UCLA121
obsid=1896
./my_program

The beginning of the perl script loads an image with the phrase

$ph_im =  "./$gal/img/${obsid}.img";

But the variables are NULL in the new program.

scripts bash environment-variables language perl

3 Answers

  1. Best Answer

    Making variables available to child process in shell script can be done either by exporting variables

    export foo=bar

    Or by calling program with variables prepended

    foo=bar ./my_prog.pl

    In either case you will need to call ENV on them inside perl script

    my $barfoo = $ENV{'foo'};
    • 19

  2. Using the environment is a cleaner way.

    There is the -s switch:

    $ cat vars.pl
#!perl
use feature 'say';
say "foo=$foo";
say "bar=$bar";

$ echo "$foo,$bar"
123,456

$ perl -s ./vars.pl -foo="$foo" -bar="$bar"
foo=123
bar=456
    • 10

  3. If you are calling it like 

    ./myscript.pl 1 35

    You can use @ARGV. E.g. 

    #!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper qw(Dumper);

print "ARGV[0]=$ARGV[0]";
print "ARGV[1]=$ARGV[1]";

print Dumper \@ARGV;

    Example source.

    This is an old example, so it may not be using the latest style. I don't have a perl compiler set up at the moment, so I can't test the output.

    You can use the Data::Dumper to help you debug things.

    If you are calling it like 

    perl -s ./myprogram -$gal="$gal" -$obsid="$obsid" 1 35

    Realize that you may get weird results mixing @ARGV and named parameters. You might want to change how you call it to something like 

    perl -s ./myprogram $gal $obsid 1 35

    or 

    perl -s ./myprogram -gal="$gal" -obsid="$obsid" -first="1" -second="35"

    Note also that the named parameters are -gal, not -$gal. I'm not quite sure what the $ would do there, but it would tend to do something other than what happens without it.

    Remember, Data::Dumper can help you debug things if you get confusing results.

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