Scalar and Text Basics

Regex Match

A match operator checks whether a scalar follows a small text pattern.

regex match A regex match returns true when text fits the pattern.

Regex Match

code
regex_match.pl
Replay: real traced execution (multi-file project)
use strict;
use warnings;

my $code = "AB-123";
my $matched = $code =~ /^([A-Z]+)-(\d+)$/;
my $matched_text = $matched ? "yes" : "no";
my $prefix = $matched ? $1 : "none";
my $number = $matched ? $2 : "none";

print "code=$code\n";
print "matched=$matched_text\n";
print "prefix=$prefix\n";
print "number=$number\n";

use strict;
use warnings;

my $code = "CD-9";
my $matched = $code =~ /^([A-Z]+)-(\d+)$/;
my $matched_text = $matched ? "yes" : "no";
my $prefix = $matched ? $1 : "none";
my $number = $matched ? $2 : "none";

print "code=$code\n";
print "matched=$matched_text\n";
print "prefix=$prefix\n";
print "number=$number\n";

use strict;
use warnings;

my $code = "bad";
my $matched = $code =~ /^([A-Z]+)-(\d+)$/;
my $matched_text = $matched ? "yes" : "no";
my $prefix = $matched ? $1 : "none";
my $number = $matched ? $2 : "none";

print "code=$code\n";
print "matched=$matched_text\n";
print "prefix=$prefix\n";
print "number=$number\n";

  1. $code ← AB-123, $matched ← 1, $matched_text ← yes, $prefix ← AB

    4my $code→ AB-123 = "AB-123"; #@code="CD-9", "bad"5my $matched→ 1 = $codeAB-123 =~ /^([A-Z]+)-(\d+)$/;6my $matched_text→ yes = $matched1 ? "yes" : "no";7my $prefix→ AB = $matched1 ? $1 : "none";8my $number→ 123 = $matched1 ? $2 : "none";910print "code=$codeAB-123\n";11print "matched=$matched_textyes\n";12print "prefix=$prefixAB\n";13print "number=$number123\n";
    outputcode=AB-123
matched=yes
prefix=AB
number=123

  1. $code ← CD-9, $matched ← 1, $matched_text ← yes, $prefix ← CD

    4my $code→ CD-9 = "CD-9";5my $matched→ 1 = $codeCD-9 =~ /^([A-Z]+)-(\d+)$/;6my $matched_text→ yes = $matched1 ? "yes" : "no";7my $prefix→ CD = $matched1 ? $1 : "none";8my $number→ 9 = $matched1 ? $2 : "none";910print "code=$codeCD-9\n";11print "matched=$matched_textyes\n";12print "prefix=$prefixCD\n";13print "number=$number9\n";
    outputcode=CD-9
matched=yes
prefix=CD
number=9

  1. $code ← bad, $matched ← (empty), $matched_text ← no, $prefix ← none

    4my $code→ bad = "bad";5my $matched→ (empty) = $codebad =~ /^([A-Z]+)-(\d+)$/;6my $matched_text→ no = $matched(empty) ? "yes" : "no";7my $prefix→ none = $matched(empty) ? $1 : "none";8my $number→ none = $matched(empty) ? $2 : "none";910print "code=$codebad\n";11print "matched=$matched_textno\n";12print "prefix=$prefixnone\n";13print "number=$numbernone\n";
    outputcode=bad
matched=no
prefix=none
number=none

Follow the Match

  1. $code starts as AB-123.
  2. The pattern looks for letters, a dash, then digits.
  3. AB-123 matches.
  4. The captures are prefix AB and number 123.
  5. The program prints matched=yes, prefix=AB, and number=123. | code | matched | prefix | number | | --- | --- | --- | --- | | AB-123 | yes | AB | 123 | | CD-9 | yes | CD | 9 | | bad | no | none | none |

Exercise: regex_match.pl

Reproduce prefix=AB and number=123, then use codes CD-9 and bad to predict the match result.