Nifty command lines: rename

This post is part of the Nifty Command Lines series.

The rename command allows you rename multiple files at once. It makes complex operations like lowercasing accessible with a single line. For simpler operations, like changing extensions from .PNG to .png, I usually reach for the action in macOS Finder.

How does rename work?

It lets you use regular expressions to batch-rename files. It looks like this:

rename -f '[regex]' [files]

Dry run

You want to remember the -n or --dry-run option. It shows you what the resulting files will be without affecting them.

Example: Replace double dashes with single ones.

~/Export ❯❯❯ rename -f 's/--/-/' * -n
'Example--1.png' would be renamed to 'Example-1.png'
'Example--2.png' would be renamed to 'Example-2.png'
'Example--3.png' would be renamed to 'Example-3.png'
'Example--4.png' would be renamed to 'Example-4.png'

The * in the command above means “all files in the current folder.” You can use glob patterns to target specific files.

To rename only .txt files, you’d write rename -f '[regex]' *.txt

Regular expressions

You write your regexes like this s/[old]/[new]/ or y/[old]/[new]/ without the square brackets.

s/ regexes are used for 1-to-1 character replacement, while y/ regexes are for complex replacements involving ranges¹. Here are some general examples.

Replacing dashes with underscores: rename -f 's/-/_/' *

It gets really powerful when you can work on character ranges:

• rename -f 'y/a-z/A-Z/' * turns all lowercase into uppercase.
• rename -f 'y/A-Z/a-z/' * turns all uppercase into lowercase.

Real-world examples

Turn filenames into URL-friendly “slugs” 🐌:

rename -f 'y/A-Z /a-z-/' *

Remove the last 𝒙 characters in a filename and replace them:

rename 's/.{𝒙}$/replacement/' *

Remove the 34 random characters that Notion’s exporter adds to Markdown files:

rename 's/.{36}$/.md/' *.md

Installation

Install it with Homebrew or apt-get: brew install rename or apt-get install rename.