Replace a token in a file from a Bash script using Perl

token_replace.sh

#!/bin/bash

perl - /var/www/html/wp-config.php <<'EOF'
use strict;
use warnings;

$^I = '.bak';
my $keys = `curl -sS https://api.wordpress.org/secret-key/1.1/salt/`;
while(<>) {
  if (/\{KEYS_TOKEN\}/){
    print $keys;
  } else {
    print;
  }
}
EOF

This snippet is derived from a larger Bash script used in an Amazon AWS CloudFormation template. The idea is that earlier in the template, the WordPress wp-config.php file is created with "{KEYS_TOKEN}" in the middle. The actual keys must be injected into the middle of the file, and not appended to the end. This code accomplishes that.