Regular Expressions

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• Often abbreviated "regex"
• Used to represent sets of strings
• Use Regex101 to test regular expressions

Examples

• abc — matches the literal “abc”.
• missing|semester — matches the string “missing” or the string “semester”.
• \d{4}-\d{2}-\d{2} — matches dates in YYYY-MM-DD format, such as “2026-01-14”. Beyond ensuring that the string consists of four digits, a dash, two digits, a dash, and two digits, this does not validate the date, so “2026-01-99” matches this regex pattern too.
• .+@.+ — matches email addresses, strings that contain some text, then an “@”, and then some more text. This does only the most basic validation and matches strings like “nonsense@@@email”. A regex that matches email addresses with no false positives or negatives exists but is impractical.