Question 1

Is this a real sed engine?

Accepted Answer

It's a small pure-JavaJavaScript sed interpreter built from scratch — no WASM, no network. It supports the seven most-used commands — s (substitute), d (delete), p (print), i (insert), a (append), c (change), n (next) — with line addressing (single line N, range N,M, last line $, /regex/ pattern addresses), BRE and ERE (-E) regex flavours, flags (g, i, p, N), -n suppress-auto-print, and -i in-place preview. For features outside this subset (e.g. hold space hHgGxNPD, branch labels, multi-line N, runtime :labels) use sed.js.org or GNU sed directly.

Question 2

How does the visual builder work?

Accepted Answer

Pick a command (substitute, delete, insert, append, change, print), fill in a small form (search, replace, line range, flags, delimiter), and the builder generates a valid sed script AND a copy-ready command `sed -E 's/foo/bar/g' file`. The auto-delimiter picks a safe separator (|, #, ~, ^) when your search or replace contains a /, so paths like /usr/local/bin don't break the command. Each command has a plain-English explanation.

Question 3

How does the auto-delimiter work?

Accepted Answer

sed's s command uses / as the default delimiter: s/search/replace/. If your search or replace string contains / (e.g. a file path), the command would break. The builder detects this and switches to a different character — | by default, then #, ~, ^, %, @, !, ;, :, ,, . — whichever doesn't appear in your strings. The generated command uses the chosen delimiter consistently: s|/usr/local/bin|/opt/bin|g.

Question 4

What about sed -i (in-place editing)?

Accepted Answer

This tool NEVER edits real files — it's a preview-only tester. But the generated command shows the correct -i syntax for both GNU sed (Linux: `sed -i 's/.../.../' file` or with backup `sed -i.bak 's/.../.../' file`) and BSD/macOS sed (`sed -i '' 's/.../.../' file` or `sed -i.bak 's/.../.../' file`). Toggle the GNU/BSD switch to see the right invocation for your platform.

Question 5

What extra features does this tool have versus sed.js.org?

Accepted Answer

(1) Pure-JS interpreter — instant load, works offline, no WASM. (2) Visual builder for s/d/p/i/a/c/n with line addressing. (3) Auto-delimiter selection (|, #, ~, ^, …) when search/replace contains /. (4) BRE vs ERE (-E) toggle with backreference helper (\1..\9 and &). (5) Per-command plain-English explanation. (6) Reverse explainer that annotates a pasted sed script. (7) GNU vs BSD/macOS -i guidance. (8) Recipe library (12 common one-liners). (9) Sample-text library (CSV, log, code, config). (10) -n suppress-auto-print flag. (11) Diff view between input and output. (12) Copy command + copy output. (13) localStorage history (max 20). (14) Shareable URL with embedded script + input. 100% client-side — preview only, never edits real files.

sed Command Builder & Tester

Output

Recipe library

How to use

Output

Recipe library