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regex

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Write, explain, test, and debug regular expressions, and build them iteratively against real sample input. Use when users want a regex/pattern to match or extract text, ask why a pattern isn't matching, need to validate emails/URLs/dates/phone numbers, or want to do find-and-replace with capture groups. Triggers on mentions of regex, regular expression, pattern, match, extract, validate, find and replace, 正则, 正则表达式, 匹配, 提取, 替换.

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Source SKILL.md: https://github.com/microclaw/microclaw/blob/HEAD/skills/built-in/regex/SKILL.md

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Regex

Never hand-wave a regex — test it against real samples before handing it over. A pattern that "looks right" but fails on the user's actual input is worse than no pattern.

Test a pattern against samples

python3 - <<'PY'
import re
pat = r'\b\d{4}-\d{2}-\d{2}\b'
samples = ["due 2026-05-31 ok", "no date", "2026/05/31 wrong sep"]
for s in samples:
    print(repr(s), "->", re.findall(pat, s))
PY

Extract with named groups

python3 - <<'PY'
import re
m = re.search(r'(?P<user>[\w.+-]+)@(?P<domain>[\w.-]+)', "ping alice.k+test@mail.example.com")
print(m.groupdict() if m else "no match")
PY

Find-and-replace with backreferences

python3 - <<'PY'
import re
print(re.sub(r'(\d{4})-(\d{2})-(\d{2})', r'\3/\2/\1', "2026-05-31"))  # -> 31/05/2026
PY

Common building blocks

  • Anchors: ^ start, $ end, \b word boundary.
  • Classes: \d digit, \w word char, \s space; negate with uppercase \D \W \S.
  • Quantifiers: * 0+, + 1+, ? 0/1, {m,n}; add ? for lazy (.*?).
  • Groups: (...) capture, (?:...) non-capture, (?P<name>...) named.
  • Lookaround: (?=...), (?!...), (?<=...), (?<!...).

Guidance

  • Always show what it matches AND what it deliberately rejects, using the user's samples.
  • Prefer explicit, readable patterns over clever unreadable ones; add re.VERBOSE for complex patterns and comment them.
  • Warn about catastrophic backtracking (nested quantifiers like (a+)+) on untrusted input.
  • Note the regex flavor if it leaves Python (JS, PCRE, Go/RE2, grep) — escaping and lookbehind support differ.
end, `\\b` word boundary.\n- Classes: `\\d` digit, `\\w` word char, `\\s` space; negate with uppercase `\\D \\W \\S`.\n- Quantifiers: `*` 0+, `+` 1+, `?` 0/1, `{m,n}`; add `?` for lazy (`.*?`).\n- Groups: `(...)` capture, `(?:...)` non-capture, `(?P\u003cname>...)` named.\n- Lookaround: `(?=...)`, `(?!...)`, `(?\u003c=...)`, `(?\u003c!...)`.\n\n## Guidance\n\n- Always show what it matches AND what it deliberately rejects, using the user's samples.\n- Prefer explicit, readable patterns over clever unreadable ones; add `re.VERBOSE` for\n complex patterns and comment them.\n- Warn about catastrophic backtracking (nested quantifiers like `(a+)+`) on untrusted input.\n- Note the regex flavor if it leaves Python (JS, PCRE, Go/RE2, grep) — escaping and\n lookbehind support differ.\n"}],"versionEndpoint":"/skill/api/version"}