This handy tool is bundled with Pike and can be executed by running pike -x rsif. This is its --help text:

rsif [options] < from >  < to >  < files >

rsif ("replace string in file") replaces all occurrences of the
string < from > with the string < to > in listed files. The name of the
files that were changed are written to stdout. Directories may be
given instead of files, in which case all the files in that directory
will be processed. Available options:

  -b, --backups   Saves the unaltered file in < filename >~
  -v, --verbose   Writes more information to stderr.
  -q, --quiet     Writes no output at all.
  -V, --version   Writes the version number of rsif.
  -h, --help      Shows this help message.