It seems Im getting somethig wrong here, since I am not very keen with Shell scripting. Here is the code which I put togheter with this forum topic:

find . -type f | while read i
do
  sed "s:<?php echo '<script language='JavaScript'>function e590206b977().*<\\\/script>'; ?>::" file > temp
  if cmp temp "$y" >/dev/null
  then
    rm temp
  else
    mv temp "$y"
  fi
done

mv: target is not directory: No such file or directory
sed: file can't be read: No such file or directory
cmp: : No such file or directory