#!/usr/bin/perl
use strict;
use warnings;

for my $file ( @ARGV ) {
    if ( ! open(INPUT, '<', $file) ) {
        warn "Unable to open $file - skipping!\n";
        next;
    }
    while ( <INPUT> ) {
        print and next if ! /\$\w+/;
        $_ =~ s/\$(\w+)/$ENV{$1}/g;
        print;
    }
}