Regular Expressions in

About Regular Expressions

Regular expressions in Gleam follow the PCRE specification (Perl Compatible Regular Expressions), similarly to other popular languages like Java, JavaScript, or Ruby.

The gleam/regex module offers functions for working with regular expressions.

The most common way to create regular expressions is using the regex.from_string function.

let assert Ok(re) = regex.from_string("test")

The regex.from_string function yields an Error if the regular expression syntax is invalid, so a let-assertion has been used here to ensure the regular expression is valid.

The regex.check function can be used to check if a regular expression matches a string.

let assert Ok(re) = regex.from_string("test")

regex.check(re, "this is a test")
// -> True

regex.check(re, "this is too")
// -> False

Captures

If you wish to capture substrings using a regular expression, the regex.scan function can be used to return a list of matches.

let assert Ok(re) = regex.from_string("[oi]n a (\\w+)")
regex.scan(with: re, content: "I am on a boat in a lake.")
// -> [
//   Match(
//     content: "on a boat",
//     submatches: [Some("boat")]
//   ),
//   Match(
//     content: "in a lake",
//     submatches: [Some("lake")]
//   )
// ]

Modifiers

The behaviour of a regular expression can be modified by creating it with the regex.compile function and passing in options.

let options = regex.Options(case_insensitive: True, multi_line: False)
let assert Ok(re) = regex.compile("[A-Z]", with: options)
regex.check(re, "abc123")
// -> True