Question

I’m trying to write a shell script which recursively goes through a directory, then in each file converts all Uppercase letters to lowercase ones. To be clear, I’m not trying to change the file names but the text in the files.

Considerations:

1. This is an old Fortran project which I am trying to make more accessible
2. I do not want to create a new file but rather write over the old one with the changes
3. There are several different file extensions in this directory, including .par .f .txt and others

What would be the best way to go about this?

Answer 1

To convert a file from lower case to upper case you can use ex (a good friend of ed, the standard editor):

ex -s file <<EOF
%s/[[:upper:]]\+/\L&/g
wq
EOF

or, if you like stuff on one line:

ex -s file <<< $'%s/[[:upper:]]\+/\L&/g\nwq'

Combining with find, you can then do:

find . -type f -exec bash -c "ex -s -- \"\$0\" <<< $'%s/[[:upper:]]\+/\L&/g\nwq'" {} \;

This method is 100% safe regarding spaces and funny symbols in the file names. No auxiliary files are created, copied or moved; files are only edited.

Edit.

Using glenn jackmann‘s suggestion, you can also write:

find . -type f -exec bash -c 'printf "%s\n" "%s/[[:upper:]]\+/\L&/g" "wq" | ex -- -s "$0"' {} \;

(the pro is that it avoids awkward escapes; the con is that it’s longer).