A regular expression, or regex, is a pattern for finding text. Small symbols can have special meanings. Regex Cheatsheet lists common symbols so you can look one up while building a pattern.
Find the symbol for a digit
Type digit in the search box. Look for \d, which means one digit such as 0 through 9 in the basic example. If you want three digits together, combine \d with {3} to make \d{3}. Search for Exactly three to find the {3} entry.
For example, \d{3} can find 123 inside x123y. If you want a whole string of three digits rather than a fragment, add ^ at the start and $ at the end: ^\d{3}$. The cheatsheet explains the pieces; use the related Regex Tester to try the complete pattern with examples that should and should not match.
Use it as a reference, not a validator
Search filters the list; it does not test your data. The Everyday patterns section contains rough starting points, not complete validators for email addresses, dates, or passwords. Regex rules can differ between JavaScript, grep, and other tools, so test the pattern in the program where you will actually use it.
Where your input goes
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Related guide
For more background, read Testing Regex Before Shipping It.
Questions you might have
- Which dialect does this describe?
- The syntax is common to most engines. Where JavaScript, PCRE and POSIX diverge, the entry says so explicitly.