Perl fc Function

last modified April 4, 2025

The Perl fc function performs Unicode case folding on strings. It returns a case-folded version of the input string.

Case folding is similar to case conversion but more comprehensive. It's used for case-insensitive string comparisons in Unicode-aware applications.

Basic fc Usage

The simplest way to use fc is on a single string.

basic.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.16.0;  # fc introduced in Perl 5.16

my $text = "Hello World";
my $folded = fc($text);

print "Original: $text\n";
print "Folded: $folded\n";

We demonstrate fc converting a string to its case-folded form. The function returns a new string without modifying the original.

$ ./basic.pl
Original: Hello World
Folded: hello world

Case-Insensitive Comparison

fc enables reliable case-insensitive string comparisons.

compare.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.16.0;

my $str1 = "Straße";
my $str2 = "STRASSE";

if (fc($str1) eq fc($str2)) {
    print "Strings are equal when case-folded\n";
} else {
    print "Strings are not equal\n";
}

This script compares German words with different cases and forms. The ß/SS equivalence is handled correctly by case folding.

$ ./compare.pl
Strings are equal when case-folded

fc vs lc/uc

fc provides more comprehensive case handling than lc.

comparison.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.16.0;

my $text = "İstanbul";

print "Original: $text\n";
print "lc: ", lc($text), "\n";
print "fc: ", fc($text), "\n";

With Turkish dotted I, fc handles the special case correctly. Simple lowercase conversion might not handle all Unicode cases properly.

$ ./comparison.pl
Original: İstanbul
lc: i̇stanbul
fc: i̇stanbul

Using fc with Arrays

fc can process array elements with map.

array.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.16.0;

my @words = ("Apple", "BANANA", "Cherry");
my @folded = map { fc } @words;

print "Original: @words\n";
print "Folded: @folded\n";

We apply fc to each array element using map. This creates a new array with case-folded versions of all strings.

$ ./array.pl
Original: Apple BANANA Cherry
Folded: apple banana cherry

Case Folding with Regular Expressions

fc can be combined with regex for advanced matching.

regex.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.16.0;

my $text = "The Greek letter Σ (sigma) has lowercase form σ or ς";

if (fc($text) =~ /ς/) {
    print "Found final sigma form\n";
}

This script demonstrates finding different sigma forms using case folding. The final sigma (ς) is matched regardless of its original case.

$ ./regex.pl
Found final sigma form

Case Folding with Hashes

fc helps create case-insensitive hash keys.

hash.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.16.0;

my %color = (fc("Red") => "#FF0000", fc("Green") => "#00FF00");

my $input = "RED";
print "$input is $color{fc($input)}\n";

We use fc to normalize hash keys and lookups. This ensures case-insensitive access to the hash values.

$ ./hash.pl
RED is #FF0000

Performance Considerations

Case folding operations can be expensive for large texts.

benchmark.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.16.0;
use Benchmark qw(cmpthese);

my $text = "ÄÖÜäöüß" x 1000;

cmpthese(-1, {
    fc => sub { my $x = fc($text) },
    lc => sub { my $x = lc($text) },
});

This benchmark compares fc with lc performance. Case folding is typically slower but more correct for Unicode text.

Best Practices

Use for comparisons: Prefer fc over lc/uc for Unicode.
Normalize early: Fold case when storing or first processing.
Combine with NFC: Consider Unicode normalization if needed.
Document usage: Note where case folding is applied.

Source

Perl fc Documentation

This tutorial covered Perl's fc function with practical examples demonstrating its usage in Unicode string handling.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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