sed Command Generator — Build & Decode sed Commands (Free)

Q: How do I find and replace text with sed?

sed 's/old/new/g' file replaces every old with new. Add -i to change the file in place (on macOS, use -i '').

Q: Why does sed -i fail on macOS?

BSD sed (macOS) requires a backup-suffix argument after -i. Use sed -i '' 's/a/b/' file — the empty string means no backup. GNU sed on Linux doesn't need it.

Q: How do I delete lines matching a pattern with sed?

sed '/pattern/d' file deletes every line containing the pattern. Add -i to apply it to the file directly.

Q: How do I replace a file path with sed?

Use a different delimiter so the slashes don't clash: sed 's#/usr/local#/opt#g' file. sed lets you use any character as the delimiter.

Generate the sed command for find-and-replace, deleting lines or printing a range — with every part explained and the -i macOS trap handled. Or paste a sed command to decode it. Runs in your browser.

The substitute command, decoded

The workhorse is s/find/replace/flags: the s means substitute, the slashes separate the parts, and the flags at the end tune it. g replaces every match on a line (without it, only the first); I makes the match case-insensitive. So sed 's/foo/bar/g' file swaps every foo for bar on each line.

The -i trap that wastes everyone an hour

-i edits the file in place instead of printing to the screen — but the two big sed versions disagree on the syntax:

GNU sed (Linux): sed -i 's/a/b/' file works.
BSD sed (macOS): needs an argument for the backup suffix — sed -i '' 's/a/b/' file. The empty '' means "no backup". Forget it and you get a cryptic "command a expects \ followed by text" error.

Tick "I'm on macOS" above and the builder adds the '' for you.

Gotchas worth knowing

The delimiter doesn't have to be /. Replacing file paths gets ugly with slashes, so use another character: sed 's#/old/path#/new/path#g'. The builder switches the delimiter automatically when your text contains /.
-i has no undo. Run it without -i first to see the output, or use -i.bak (GNU) to keep a backup copy.
Special characters need escaping or -E. Plain sed uses basic regex where +, ? and () need backslashes. Add -E to use them normally.
Printing needs -n. sed prints every line by default, so to print only a range you suppress the default with -n and add p.

Frequently asked questions

How do I find and replace text with sed?

sed 's/old/new/g' file replaces every old with new. Add -i to change the file in place (on macOS, -i '').

Why does sed -i fail on macOS?

BSD sed requires a backup-suffix argument after -i. Use sed -i '' 's/a/b/' file — the empty string means no backup.

How do I delete lines matching a pattern?

sed '/pattern/d' file deletes every line containing the pattern. Add -i to apply it to the file.

How do I replace a file path with sed?

Use a different delimiter so the slashes don't clash: sed 's#/usr/local#/opt#g' file.

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sed Command Generator — Build & Decode sed Commands

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