Find and Replace: A Practical Guide

The core idea

Find and replace searches a text for a pattern and swaps every match for something else. It is the fastest way to fix a repeated mistake, rename something, or reshape data.

The options that matter

• Case: whether Apple and apple count as the same.
• Whole word: whether cat may match inside category.
• Replace all or one: every match, or one at a time with a check.
• Literal or regex: exact text, or a pattern.

In common programs

• Microsoft Word, Excel and Google Docs: press Ctrl+H.
• VS Code: Ctrl+H in a file, Ctrl+Shift+H across a whole project. Use the buttons for case, whole word and regex.
• Notepad++: Ctrl+H, with an option for regular expressions.

On the command line

# Linux and macOS: replace in a file
sed -i 's/old/new/g' file.txt

# PowerShell
(Get-Content file.txt) -replace 'old', 'new' | Set-Content file.txt

# Python
text.replace("old", "new")
re.sub(r"\d+", "#", text)

The sed option -i edits the file in place, so keep a backup first. On macOS, the form is sed -i with an empty backup suffix argument.

Common mistakes

• Replacing part of a longer word: use whole-word matching.
• Unescaped special characters: in regex mode a dot matches any character, so write \. for a real full stop.
• Order problems: when running several replacements, an earlier one can change what a later one sees. Swaps need an all-at-once approach.
• No backup: always keep the original until you have checked the result.

Try it here

Use find and replace for a single change, find and replace multiple for a list, regex find and replace for patterns, and case-insensitive replace to keep capitalisation.