Regex Cheat Sheet

Characters

• Any character Any single character except a line break.Copy .
• Digit One digit, 0 to 9.Copy \d
• Word character A letter, a digit or an underscore.Copy \w
• Whitespace A space, a tab or a line break.Copy \s
• One of these A single a, b or c. [a-z] is any lowercase letter.Copy [abc]
• None of these Any single character except a, b or c.Copy [^abc]

How many

These apply to whatever comes right before them. By default they grab as much as they can; add ? to grab as little as possible.

• Zero or more The previous item any number of times, including none.Copy *
• One or more The previous item at least once.Copy +
• Optional The previous item once or not at all.Copy ?
• Exactly n The previous item exactly 3 times.Copy {3}
• Between n and m From 2 to 5 times. {2,} means 2 or more.Copy {2,5}
• As few as possible Lazy match: stop at the first place the rest of the pattern fits.Copy .*?

Position and choice

• Start The start of the text, or of each line with the m flag.Copy ^
• End The end of the text, or of each line with the m flag.Copy $
• Word boundary cat as a whole word, not inside category.Copy \bcat\b
• Either one Matches cat or dog.Copy cat|dog
• Literal symbol A backslash makes a special character ordinary. Here: a real dot.Copy \.
• The opposite Capital letters invert: not a digit, not a word character, not whitespace.Copy \D \W \S

Groups

• Capture Treat abc as one unit and remember what it matched.Copy (abc)
• Group, no capture Group without remembering. Use it when you only need the grouping.Copy (?:abc)
• Named group Capture under a name instead of a number.Copy (?<year>\d{4})
• Same text again Backreference: the same text the first group matched. Here, a doubled letter.Copy (\w)\1
• Use in a replacement In the replacement text, whatever group 1 matched. Python writes \1.Copy $1
• Optional group The whole group may be there or not.Copy (abc)?

Lookarounds and flags

Lookarounds check what is next to the match without including it in the result.

• Followed by Digits, but only when px comes right after. px is not part of the match.Copy \d+(?=px)
• Not followed by Digits that are not followed by px.Copy \d+(?!px)
• Preceded by Digits that come right after a dollar sign.Copy (?<=\$)\d+
• Not preceded by Digits that do not come right after a dollar sign.Copy (?<!\$)\d+
• Ignore case The i flag: abc, ABC and Abc all match.Copy /abc/i
• Every match The g flag: find all matches, not just the first.Copy /abc/g

Ready-made patterns

• Email, simple Something, an @, something, a dot, something. Good enough for a form.Copy ^[^@\s]+@[^@\s]+\.[^@\s]+$
• Whole number Only digits, with an optional minus sign.Copy ^-?\d+$
• Date, YYYY-MM-DD The shape of an ISO date. It does not check that the date exists.Copy ^\d{4}-\d{2}-\d{2}$
• Hex color A 3 or 6 digit hex color, with or without the #.Copy ^#?([0-9a-fA-F]{3}|[0-9a-fA-F]{6})$
• URL Anything that starts with http:// or https://, up to the next space.Copy https?://[^\s]+
• Extra spaces Two or more whitespace characters in a row. Replace with one space to clean up text.Copy \s{2,}