Regular Expressions in Perl

Regular expressions are built into Perl at the language level, which is a big part of why Perl is so good at text. Here’s what you actually need.

Matching

The =~ operator binds a string to a pattern. // is the match:

my $text = "The order shipped on 2026-07-08";
if ($text =~ /shipped/) {
    print "it shipped\n";
}

Capture groups

Parentheses capture parts of the match into $1, $2, …:

if ($text =~ /(\d{4})-(\d{2})-(\d{2})/) {
    print "year=$1 month=$2 day=$3\n";   # year=2026 month=07 day=08
}

Substitution

s/// replaces matched text:

my $s = "colour and flavour";
$s =~ s/our/or/g;   # "color and flavor" (g = replace all)

The modifiers you’ll use

• g — global: match/replace every occurrence, not just the first.
• i — case-insensitive.
• m — multiline: ^ and $ match at line breaks within the string.
• s — single line: . also matches newlines.
• x — extended: ignore whitespace in the pattern so you can space it out and comment it.

$text =~ /
    (\d{4}) - (\d{2}) - (\d{2})   # an ISO date
/x;

The building blocks

Pattern	Matches
\d \w \s	digit, word char, whitespace
\D \W \S	the negations
.	any character (except newline)
* + ?	zero-or-more, one-or-more, optional
{2,5}	between 2 and 5 times
^ $	start / end of string (or line with /m)
[abc]	any one of a, b, c
(a|b)	a or b
\b	a word boundary

Extracting every match

In list context with /g, a match returns all captures — great for pulling structured data out of text:

my $log = "ip 10.0.0.1 ip 10.0.0.2 ip 10.0.0.9";
my @ips = $log =~ /ip (\S+)/g;   # ("10.0.0.1", "10.0.0.2", "10.0.0.9")

A practical tip

Prefer specific patterns over greedy ones. .* is greedy and will grab as much as it can; use .*? (non-greedy) or a precise character class like [^"]* when parsing delimited text.

Where to go next

Put regexes to work at the command line in Perl One-Liners for Text Processing.