An example of a no-dependency template in Perl

hydrate.pl

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

# hydrate: poor man's templating
#
# usage: hydrate key1=value1 key2=value2 ... path/to/file.in > path/to/file.out
#
# substitutes all strings '{{key1}}' in file.in with 'value1'

my $file = pop @ARGV;
my %kv   = map { split /=/ } @ARGV;

open my $fh, "<", $file
  or die "Unable to open '$file': $!\n";
while (my $line = <$fh>) {
    $line =~ s/\{\{(\S+?)\}\}/$kv{$1}/g;
    print $line;
}
close $fh;

template.json

{
  "host": "{{mysql_host}}",
  "username": "{{mysql_user}}",
  "password": "{{mysql_pass}}"
}