Perl Regular Expressions Guide — Pattern Matching and Text Processing

use strict;
use warnings;

my $text = "The quick brown fox jumps over the lazy dog.";

# Simple match
if ($text =~ /quick/) {
    print "Found 'quick'\n";
}

# Case-insensitive
if ($text =~ /THE/i) {
    print "Case-insensitive match\n";
}

# Match anywhere (default behavior)

my $text = "Name: Alice, Age: 30, City: New York";

# Parentheses capture
if ($text =~ /Name: (\w+), Age: (\d+)/) {
    print "Name: $1, Age: $2\n";  # Alice, 30
}

# Named captures (Perl 5.10+)
if ($text =~ /Name: (?<name>\w+), Age: (?<age>\d+)/) {
    print "Name: $+{name}, Age: $+{age}\n";
}

my $s = "Hello world, hello Perl";

# Simple substitution
(my $modified = $s) =~ s/hello/hi/;
print "$modified\n";  # Hi world, hello Perl

# Global substitution
(my $global = $s) =~ s/hello/hi/gi;  # case-insensitive
print "$global\n";  # Hi world, hi Perl

# In-place modification
$s =~ s/Perl/Lua/;

# /i  - case insensitive
# /g  - global (all occurrences)
# /m  - multiline (^ and $ match line boundaries)
# /s  - single line (. matches newline)
# /x  - extended (allow whitespace and comments)
# /o  - compile once

my $text = "Line 1\nLine 2\nLine 3\n";
my @matches = $text =~ /^Line \d+$/gm;  # all 3 lines

my $text = "Email: user@example.com, Phone: 555-1234";

# Alternation
if ($text =~ /Email|Phone/) { }

# Character classes
if ($text =~ /[A-Z]/) {}  # uppercase letter
if ($text =~ /[0-9]/) {}  # digit
if ($text =~ /[^0-9]/) {} # not a digit

# Quantifiers
# *  - zero or more
# +  - one or more
# ?  - zero or one
# {n} - exactly n
# {n,} - n or more

# Non-greedy
my $html = "<b>Bold</b> and <i>italic</i>";
my ($greedy) = $html =~ /<b>(.*?)<\/b>/;  # non-greedy