Learn

Groovy has regex literals, operators, and a smooth API on top of Java's regex.

Regex literals

def pattern = ~/\d+/        // pattern compiled at parse time
def alt = ~"\\d+"           // alternative — escape backslashes

The ~/.../ syntax produces a java.util.regex.Pattern.

Match operators

"hello123" =~ /\d+/         // creates a Matcher
"hello123" ==~ /[a-z]+/      // exact match — boolean
"hello123" =~ /\d+/ ? "contains digits" : "no digits"

• =~ — find any match (returns Matcher)
• ==~ — exact full-string match (returns boolean)

Extracting captures

def m = "name: Ada, age: 36" =~ /name: (\w+), age: (\d+)/
if (m) {
    def name = m[0][1]      // first match, first capture group
    def age = m[0][2]
    println "$name is $age"
}

m[0] is the first match (whole match + groups). m[0][0] is the full match, m[0][1..n] are the groups.

Find all matches

def matcher = "phone 555-1234 fax 555-5678" =~ /\d{3}-\d{4}/
matcher.each { println it }    // "555-1234", "555-5678"

// Or collect:
def numbers = ("phone 555-1234" =~ /\d+/).findAll()
// ["555", "1234"]

Replace

def s = "hello world"
s.replaceAll(/o/, "0")           // "hell0 w0rld"

// With closure for dynamic replacement:
s.replaceAll(/\w+/) { match ->
    match.toUpperCase()
}
// "HELLO WORLD"

Common patterns

// Email-ish
~/[\w.-]+@[\w.-]+/

// URL-ish
~/https?:\/\/[\w.-]+(\/.*)?/

// Date
~/\d{4}-\d{2}-\d{2}/

// Numbers
~/\d+/
~/\d+\.\d+/

Multi-line, case-insensitive, etc.

Use Java's flag syntax inside the pattern:

• (?i) — case-insensitive
• (?s) — dot matches newlines
• (?m) — multiline (^ and $ per line)

"HELLO" ==~ /(?i)hello/      // true