#!/usr/bin/perl -w
use strict;

my $cmd = shift;

while (my $filename = shift) {
  # Perform operation to new file.  Exit on error.
  # TODO:  On error, report command that caused problem and the resulting
  #        error message before dying.
  die if `$cmd $filename 2>&1 >$filename.new`;

  # If the output is different than the input, replace the old version with
  # the new one.  If nothing was changed, discared the new version and leave
  # the old one untouched.
  if (`diff $filename.new $filename`) {
    rename "$filename.new", $filename;
  } else {
    unlink "$filename.new";
  }
}