subs.sh

#!/bin/bash

if [ -z "$1" -o -z "$2" ]; then
   echo "Usage: substitue FROM_STRING TO_STRING [OPTION]..."
   echo
   echo "Replace all occurances of FROM_STRING (a sed-compatible regular"
   echo "expression) with TO_STRING in all files for which ack matches"
   echo "FROM_STRING."
   echo
   echo "Any additional options are passed directly to ack (e.g.,"
   echo " --type=html would only run the substitution on html files)."
   exit 1
fi

# Escape forward slashes for sed
FROM_STRING=${1//\//\\/}
TO_STRING=${2//\//\\/}
shift 2
ack -l --print0 "$@" "$FROM_STRING" | xargs -0 -n 1 sed -i -e "s/$FROM_STRING/$TO_STRING/g"

Fixed line 16 & 17 to escape all occurences of / not only the first one