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Grep Tool

Grep is the classic Unix tool for searching plain text — given a pattern (literal or regex), it returns the lines that match. The ZTools Grep Tool brings the same capability to the browser: paste any text, pattern (literal substring or JavaScript regex), and get the matching lines highlighted plus a match count. Useful when you don't have a terminal, or when the input is in your clipboard rather than a file. Supports case-insensitive matching, inverse match (lines that DON'T contain the pattern), context lines (-A / -B / -C), whole-word match, and line-number prefix.

Use cases​

Filter a paste of log lines​

Shell access not available; you have a 5,000-line log paste from a colleague. Grep for ERROR — see only the failures.

Find usages in pasted code​

Pasted a 1000-line file from a screen-share. Grep for "TODO" or a specific function name — instant locator.

Filter CSV rows by pattern​

Need rows where the email column contains "@gmail.com". Grep with regex — cleaner than loading into a spreadsheet.

Test a regex​

Paste sample text, enter the pattern, see what matches. Faster feedback loop than running grep in a shell repeatedly.

How it works​

  1. Paste input — Up to several MB of text. Tool stores in memory only.
  2. Enter pattern — Literal substring (default) or JavaScript regex (toggle). Regex flags: i (case-insensitive), m (multiline), u (unicode).
  3. Configure mode — Inverse (-v: lines NOT matching), word boundary (-w), max results, context before / after / around matched lines.
  4. Read output — Matching lines with optional line-number prefix. Highlight on the matched span. Match count shown at the top.

Examples​

Input: Pattern: ERROR; input: 1000 log lines

Output: Output: only lines containing "ERROR", line numbers prefixed, count e.g. 47 matches.

Input: Regex: ^\\d{4}-\\d{2}-\\d{2}

Output: Returns only lines starting with a YYYY-MM-DD date — useful for filtering log entries by date format.

Input: Inverse match: pattern "DEBUG", flag -v

Output: Returns all lines that DON'T contain DEBUG — drop the noisy debug lines.

Input: Context: -C 2 around match

Output: Each match shows the 2 lines before and 2 lines after — better situational context for log triage.

Frequently asked questions​

Is this real grep or a JavaScript imitation?

JavaScript imitation. Most flags work the same way. Differences: JS regex syntax (no PCRE backreferences in some engines), no file I/O, no recursive directory grep.

PCRE vs JS regex?

JavaScript regex. Look-behind requires modern browsers; named groups supported. For PCRE-only features (recursive patterns, conditionals), use a desktop tool.

How big an input can it handle?

Several MB is fine. 100+ MB causes the browser to lag — use a CLI grep instead.

Privacy?

Input never leaves the browser. No upload, no logging.

Can it grep across multiple files?

Single input only. For multi-file search, use ripgrep or VS Code search.

Tips​

  • Use word-boundary mode (-w) when searching for short identifiers — avoids matches inside longer words.
  • Test regex against a few sample lines first — incremental feedback beats running on the full file with a wrong pattern.
  • Inverse match (-v) is the fastest way to drop noise (DEBUG lines) and focus on signal (WARN/ERROR).
  • For huge inputs (>10 MB), prefer ripgrep CLI — designed for speed and handles GBs gracefully.

Try it now​

The full Grep Tool runs in your browser at https://ztools.zaions.com/grep-tool — no signup, no upload, no data leaves your device.

Open the tool ↗

Last updated: 2026-05-06 · Author: Ahsan Mahmood · Edit this page on GitHub