How to replace a string in an existing file in Perl while not touching unchanged files

Question

Using

perl -pi -e 's/pattern/replacement/g' $(find src -type f)

is nice, except for one thing: All files get overwritten, even those without any match. This is not good as I often keep many of them open in Emacs or Eclipse which then ask me boring questions. Is there a simple way how to prevent touching unchanged files (Something like using grep in find is too much work, especially for complex patterns).

Answer 1

The very first thing -i after opening a file is to unlink it, so that means you can't use -i on the files you don't want to modify.

find src -type f -exec grep -Pl 'pattern' {} + |
   xargs perl -i -pe's/pattern/replacement/g'

Of course, grep can already perform recursive searches, so unless you need to use find to filter the results further than you indicated, you can use

grep -Plr 'pattern' src |
   xargs perl -i -pe's/pattern/replacement/g'

---

Note: cmd | xargs perl ... can handle more files than perl ... $( cmd ).

Answer 2

Instead of passing every file to perl to be processed, preselect them yourself.

Find the files that have pattern in them:

grep -Plr 'pattern' src

Then use that instead of that find call:

perl -pi -e 's/pattern/replacement/g' $(grep -Plr pattern src)

Or even like this:

grep -Plr 'pattern' src | xargs perl -pi -e's/pattern/replacement/g'

This will also probably be faster because you're not processing files unnecessarily.