Regular expressions are a powerful tool — if you know how. Practical cheat sheet to bookmark.
Basic Characters¶
. \d \D \w \W \s \S \b
Quantifiers¶
* + ? {3} {2,5} {3,} *?
Groups¶
(abc) (?:abc) a|b \1
Lookahead/behind¶
(?=x) (?!x) (?<=x) (?<!x)
Examples¶
Email: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,}
IP: \b(?:\d{1,3}.){3}\d{1,3}\b
Date: \d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])
Phone CZ: (?:+420)?\s?\d{3}\s?\d{3}\s?\d{3}
In Practice¶
grep -oP ‘\b\d{1,3}(.\d{1,3}){3}\b’ access.log
import re; emails = re.findall(r’[\w.+-]+@[\w-]+.[\w.]+’, text)
Tip¶
Test on regex101.com. And if regex exceeds 2 lines, consider a parser.
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