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

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.

3 Answers

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'};

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

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.