Flags in Regex

Flags are options we can apply to a regular expression to change its matching behavior.

These options can be specified at the beginning of the regular expression, after a forward slash or in parentheses, depending on the programming language used.

Some of the most common flags are:

Modifier g (Global Match)

Matches throughout the entire text (not just the first occurrence).

Modifier i (Case Insensitive)

Ignores case sensitivity in the search.

Here, the Regex selects all variants of “hola”, regardless of case.

Modifier m (Multi-line)

Allows ^ and $ to match the start and end of lines (not just the entire string)

Here, ^La selects the word “La” that appears at the beginning of each line, not just at the start of the text.

Modifier s (Dot All)

Allows the dot (.) to match newline characters (\n), in addition to any other character.

Here, the regex selects the text between “Hola” and “mundo”, even crossing lines due to the s modifier.

Modifier u (Unicode)

Enables full matching of Unicode characters.

Here, \p{L} selects any Unicode letter, such as ñ, é, and ß.

Modifier x (Verbose)

Allows comments and whitespace within the regex for better readability. Comments are placed with #.

Here, all numbers with more than one digit are selected, while the comment after # does not affect the regex.