env.pl

#!/usr/local/bin/perl

##
# @file      env.pl
# @author    Mitch Richling <http://www.mitchr.me/>
# @Copyright Copyright 1995 by Mitch Richling.  All rights reserved.
# @brief     How to access environment variables@EOL
# @Keywords  UNIX shell environment variable perl
# @Std       Perl5
#
#            This Perl program is intended to illustrate how one can
#            query and modify environment variables.

# One way to query the SHELL environment variable.
printf("SHELL=%s\n", $ENV{'SHELL'});

# To tell the diffrence between a NULL value and an undefined environment variable:
if(defined($ENV{'FOO'})) {
  printf("The SHELL variable is set to: %s\n", $ENV{'FOO'});
} else {
  print "The variable FOO was NOT defined.\n";
}

# You can clear a variable like this:
printf("Clearing SHELL\n");
$ENV{'SHELL'} = '';
printf("SHELL=%s\n", $ENV{'SHELL'});

# You can Set an environment variable like this:
printf("Setting SHELL=/bin/foo\n");
$ENV{'SHELL'} = '/bin/foo';
printf("SHELL=%s\n", $env{'SHELL'});

# You can add something to the PATH environment variable like so:
printf("PATH=%s\n", $ENV{'PATH'});
# This is complex because we need a : if PATH is non-empty,
# otherwise we only need to set PATH equal to what we want.
$ENV{'PATH'} .= (($ENV{'PATH'} ? ':' : '') . '/usr/local/bin');
printf("PATH=%s\n", $ENV{'PATH'});