Regex to Match Programming Variable Names

This regex validates variable names (identifiers) as used in most programming languages including JavaScript, Python, Java, and C. Here is the token-by-token breakdown:

^ — Anchors the match at the start of the string.

[a-zA-Z_$] — A character class matching the first character of the variable name. It allows uppercase letters (A-Z), lowercase letters (a-z), underscore (_), and dollar sign ($). Most programming languages require identifiers to start with a letter, underscore, or (in JavaScript) a dollar sign. Digits are not allowed as the first character to prevent ambiguity with numeric literals.

[a-zA-Z0-9_$]* — A character class matching the remaining characters. It allows the same characters as the first class plus digits (0-9). The * quantifier allows zero or more characters, so single-character names like 'x' or '_' are valid.

$ — Anchors the match at the end of the string.

This pattern covers the common identifier rules shared by most C-family languages. It matches names like 'myVariable', '_privateField', '$jQueryElement', 'MAX_SIZE', and 'x1'. It does not match names starting with digits like '2nd' or names containing spaces or special characters. Note that this pattern does not check for reserved words (keywords). A variable name might match this regex but still be invalid if it conflicts with a language keyword like 'class' or 'return'. Keyword checking requires a separate validation step.