grex

Properties1
tagstools, cli, regex, rust

grex generates a regular expression from a set of test strings — the inverse of writing a regex by hand. Feed it example inputs and it produces a pattern that matches all of them (and only them, by default), written in Rust for speed.

Basic Syntax

grex <string>...
grex -f <file>

Strings can be passed directly as arguments, read from a file (one per line) with -f, or piped via stdin with -.

Common Options

  • -f <file> — Read test strings from a file, one per line.
  • -i, --ignore-case — Case-insensitive matching.
  • -r, --repetitions — Detect repeated substrings and convert to {min,max} quantifiers.
  • -d, --digits / -D, --non-digits — Convert Unicode digits to \d / non-digits to \D.
  • -s, --spaces / -S, --non-spaces — Convert whitespace to \s / non-whitespace to \S.
  • -w, --words / -W, --non-words — Convert word characters to \w / non-word chars to \W.
  • -e, --escape — Replace non-ASCII characters with unicode escape sequences.
  • -g, --capture-groups — Replace non-capturing groups with capturing ones.
  • --no-start-anchor / --no-end-anchor / --no-anchors — Drop the ^ / $ / both anchors.
  • -x, --verbose — Nicer-looking, commented output.
  • -c, --colorize — Syntax-highlight the resulting regex.

By default the output is anchored (^...$) and matches only the given test cases exactly.

Cheatsheet

grex foo foobar foobarbaz # ^foo(?:bar(?:baz)?)?$
grex -f <file> # generate from a file, one test string per line
echo -e "a1\nb2\nc3" | grex - # generate from stdin
grex -i Foo foo FOO # (?i)^foo$
grex -r a aa aaa # collapse repeats into quantifiers, e.g. ^a{1,3}$
grex -d a1 b2 c3 # use digit class, e.g. ^[a-c]\d$
grex --no-anchors foo bar # drop ^ and $ for substring matching

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