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Nifty command lines: rename

──── 2 mins#CLI

Last Updated: February 23, 2021

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.


  1. If you want to dig into these (I never did), know that they’re Perl regexes.