Perl Environment Variable Loader

loadEnv.pl

#!/usr/bin/perl

# Take in a file containing environment variables line by line
# and if the variable is not yet set print out an export command
# that can be evaluated by bash. This allows us to specify environment
# values in a much easier format than otherwise allowed.  For example:
#
#    # Comments are expressed with a leading hash sign and on their own line.
#    # Empty lines are ok.
#
#    # Values will be trimmed so lining up spaces will work as expected.
#    # Each non-blank, non-comment line will be split on the first white
#    # space character and spaces after that are ok.
#    MY_ENV_VAL   -MX:400 -BD200
#    EVAL2        BLAH
#
#    # Empty string environment values are possible by just specifying a name
#    BLANK_ENV_VAL
#
# This file would output:
#    export MY_ENV_VAL='-MX:400 -BD200'
#    export EVAL2='BLAH'
#    export BLANK_ENV_VAL=''
#
# But if any of the values were already in the environment the line would be
# skipped.  To run this file within a docker run file you would call it like:
#
#   eval $(loadEnv /my/env/file.txt)
#

use strict;
use warnings;

sub trim {
  my $s = shift;
  $s =~ s/^\s+|\s+$//g;
  return $s
};

my $num_args = $#ARGV + 1;
if ($num_args != 1) {
    print "\nUsage: loadEnvFile.pl [filename]\n";
    exit 1;
}

my $file = $ARGV[0];
open my $info, $file or die "Could not open $file: $!";

my $varName;
my $varValue;

while( my $line = <$info>)  {
  $line = trim($line);
  if ($line =~ /^\#/) {
    next;
  } else {
    my @words = split /\s+/, $line, 2;
    if (scalar @words > 0) {
      $varName = trim($words[0]);
      $varValue = "";
      if (scalar @words == 2) {
        $varValue = trim($words[1]);
      }
      if (! defined $ENV{$varName}) {
        print "export $varName='$varValue'\n";
      }
    }
  }
}

close $info;

Could enhance with escaping special characters later:

  sub esc_chars {
    # will change, for example, a!!a to a\!\!a
    @_ =~ s/([;<>\*\|`&\$!#\(\)\[\]\{\}:'"])/\\$1/g;
    return @_;
  }