Here's a one-liner for changing a bunch of filenames all at once. Say you've got a bunch of .jsx files, but you agree with the React team that the .jsx file extension has outlived its usefulness. How do you rename all those files to end in .js?

Like this:

For readability, on multiple lines it looks like this:

This code works by embedding the output of subshells as strings. The first subshell runs a very simple command which gets a list of files:

The next does something more complicated:

This runs the s/jsx/js regular expression pattern substitution through sed. Note that the -E option is specific to macOS. On other operating systems, you might need -e or other command-line flags instead. When I wrote this command, I spent ten seconds writing everything else, and about 15 minutes tracking down the right syntax for sed.

Anyway, sed stands for "stream editor", so if you pipe the output of echo SomeComponent.jsx into sed like this, it's going to edit that stream and pass it through as the string SomeComponent.js. Since $() passes along its subshell output as a string, that becomes:

And because it's iterating over your ls subshell, you'll run that for every .jsx file in your src/ directory.