til/unix/reverse-each-line-of-a-file.md

Reverse Each Line Of A File

The rev command can be used to reverse each line in a file. Every line is left where it is relative to other lines, but the contents of each line is reversed.

So a file that contains the following text:

❯ cat stuff.md
Three
Two
One
go racecar go

can be piped to rev to get the following output:

❯ rev stuff.md
eerhT
owT
enO
og racecar og

This is an odd utility that doesn't have too much use that I can imagine. After a brief chat with Claude where I asked for some practical use cases, the one that stood out the most to me is to reverse a list of filenames, sort them, and then reverse them again (putting them back in readable order). This can shuffle filenames with similar endings near each other like source and test files.

Here is a list of files for me py-vmt project:

❯ fd -t f .
README.md
pyproject.toml
src/py_vmt/__init__.py
src/py_vmt/cli.py
src/py_vmt/session.py
src/py_vmt/time_helpers.py
tests/src/py_vmt/test_cli.py
tests/src/py_vmt/test_session.py

Now I can pipe the output of that fd command through rev | sort | rev to get my files organized in a different way.

❯ fd -t f . | rev | sort | rev
README.md
pyproject.toml
src/py_vmt/__init__.py
tests/src/py_vmt/test_cli.py
src/py_vmt/cli.py
tests/src/py_vmt/test_session.py
src/py_vmt/session.py
src/py_vmt/time_helpers.py

Again the value of doing something like this is a bit tenuous. At the very least it is fun to know about.