RegExp Class

RegExp is Alia's built-in regular expression class, used for pattern matching, text search, and replacement operations.

Creating Regular Expressions

Pattern Only

const re = new RegExp ['\\d+']

Pattern with Flags

const re = new RegExp ['hello', 'gi']

From an Object

const re = new RegExp [*[pattern: '\\w+', flags: 'i']]

Creating an Empty Regex

const re = new RegExp

Instance Properties (Read-Only)

Property	Type	Description
pattern	String	The regex pattern string
flags	String	The flags string
global	Boolean	Whether the g flag is set
multiline	Boolean	Whether the m flag is set
ignoreCase	Boolean	Whether the i flag is set
unicode	Boolean	Whether the u flag is set
sticky	Boolean	Whether the y flag is set
dotAll	Boolean	Whether the s flag is set (. matches newlines)

Instance Methods

test

Tests whether a string matches the regex. The signature is re.test input; it takes a single string argument and returns a Boolean.

const re = new RegExp ['\\d+']
print re.test 'abc123'  ~ true
print re.test 'abc'     ~ false

exec

Performs a matching search. The signature is re.exec input; it takes a single string argument, returning Null when there is no match and a details object on a match.

const re = new RegExp ['(\\d+)-(\\d+)']
const m = re.exec '2024-01-15'
if typeOf m == 'Object' {
  print m.index     ~ 0
  print m.matched   ~ '2024-01'
  print m.groups    ~ ['2024', '01']
}

Return value structure: *[index: Number, matched: String, groups: Array]

match

The signature is re.match input; it takes a single string argument and returns the match results, or Null when there is no match.

Non-global mode returns a nested single-element array:

const re1 = new RegExp ['\\d+']
print re1.match 'a12b'  ~ [[*[index: 1, matched: '12', groups: []]]]

Global mode returns all matches:

const re2 = new RegExp ['\\d+', 'g']
print re2.match 'a12b34'  ~ [*[index: 1, matched: '12', groups: []], *[index: 4, matched: '34', groups: []]]

replace

Replaces matched content. The signature is re.replace input with replacement; it takes the input string joined to the replacement string with with and returns a String.

const re = new RegExp ['\\d+']
print re.replace 'a12b34' with 'X'  ~ 'aXb34'

const re2 = new RegExp ['\\d+', 'g']
print re2.replace 'a12b34' with 'X'  ~ 'aXbX'

split

Splits a string by the pattern. The signature is re.split input; it takes the input string and returns an Array.

const re = new RegExp [',\\s*']
print re.split 'a, b, c'  ~ ['a', 'b', 'c']

The number of returned results can be limited by attaching limit with an upper bound:

const re = new RegExp [',\\s*']
print re.split 'a, b, c, d' limit 2  ~ ['a', 'b']

Static Methods

RegExp.escape

Escapes regex special characters in a string. The signature is RegExp.escape input; it takes a single string argument and returns a String.

const escaped = RegExp.escape 'price: $10.00'
print escaped  ~ 'price: \$10\.00'

Complete Example

~ Create regexes
const email = new RegExp ['[\\w.]+@[\\w.]+\\.[a-z]{2,}', 'i']
const digits = new RegExp ['\\d+', 'g']

~ Test matching
print email.test 'user@example.com'  ~ true

~ Replace
print digits.replace 'abc 123 def 456' with '#'  ~ 'abc # def #'

~ Split
const sep = new RegExp [',\\s*']
const parts = sep.split 'a, b, c'
print parts  ~ ['a', 'b', 'c']

~ Match
const matcher = new RegExp ['\\d+', 'g']
const nums = matcher.match 'a12b34'
print nums  ~ [*[index: 1, matched: '12', groups: []], *[index: 4, matched: '34', groups: []]]

~ exec
const re = new RegExp ['(\\d+)-(\\d+)']
const m = re.exec '2024-01-15'
if typeOf m == 'Object' {
  print m.index    ~ 0
  print m.matched  ~ '2024-01'
  print m.groups   ~ ['2024', '01']
}

~ Properties
print email.global       ~ false
print email.ignoreCase   ~ true
print email.pattern      ~ '[\\w.]+@[\\w.]+\\.[a-z]{2,}'

~ Static methods
print RegExp.escape '$10.00'  ~ '\\$10\\.00'

Flag Reference

Flag	Property name	Description
g	global	Global matching
i	ignoreCase	Case-insensitive matching
m	multiline	Multiline mode
s	dotAll	. matches newlines
u	unicode	Unicode mode
y	sticky	Sticky matching