Regular expressions pcre2 cheatsheet
Regular expressions pcre2: Using regex in tools
7 common Regular expressions pcre2 tasks.
Search with grep
Print lines made only of digits. -E enables extended regular expressions.
grep -E '^[0-9]+$' file.txt
Use lookarounds with grep
Print only the matching part, using Perl-compatible syntax with -P (GNU grep).
grep -oP '\d+(?=px)' styles.css
Rewrite text with sed
Swap two numbers around a hyphen, using capture groups in the replacement.
sed -E 's/([0-9]+)-([0-9]+)/\2-\1/' file.txt
Match in JavaScript
Extract the parts of a date with a regular expression literal.
const [, year, month, day] = "2026-10-30".match(/(\d{4})-(\d{2})-(\d{2})/);
Replace in JavaScript
Replace every run of whitespace with a single space. The g flag replaces all matches.
text.replace(/\s+/g, " ")
Find all matches in Python
Return every run of digits in a string. Use raw strings so backslashes aren't treated as escapes.
import re
re.findall(r"\d+", text)
Replace in Python
Replace matches using a pattern and a replacement, with \1 style references.
re.sub(r"(\d{4})-(\d{2})-(\d{2})", r"\3/\2/\1", text)