Perl uc Function

last modified April 4, 2025

The Perl uc function converts all characters in a string to uppercase. It's a built-in string manipulation function that handles locale-specific case conversion.

uc returns a new string and doesn't modify the original. For in-place modification, Perl provides the uc in combination with assignment.

Basic uc Usage

The simplest way to use uc is on a single string variable.

basic.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.34.0;

my $text = "Hello World";
my $upper = uc($text);

print "Original: $text\n";
print "Uppercase: $upper\n";

We demonstrate uc converting a string to uppercase. The original string remains unchanged while a new uppercase version is created.

$ ./basic.pl
Original: Hello World
Uppercase: HELLO WORLD

In-Place Conversion

To modify a string directly, combine uc with assignment.

inplace.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.34.0;

my $text = "perl programming";
print "Before: $text\n";

$text = uc($text);
print "After: $text\n";

This shows how to convert a string to uppercase while modifying the original variable. The assignment replaces the original value.

$ ./inplace.pl
Before: perl programming
After: PERL PROGRAMMING

Locale Awareness

uc respects the current locale settings for case conversion.

locale.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.34.0;
use locale;

my $text = "straße";  # German street
my $upper = uc($text);

print "Original: $text\n";
print "Uppercase: $upper\n";

With use locale, uc handles special characters correctly according to the current locale. The German ß becomes SS.

$ ./locale.pl
Original: straße
Uppercase: STRASSE

Array Processing

uc can process array elements with map.

array.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.34.0;

my @words = ("apple", "banana", "cherry");
my @upper = map { uc } @words;

print "Original: @words\n";
print "Uppercase: @upper\n";

We use map to apply uc to each array element. This creates a new array with all elements converted to uppercase.

$ ./array.pl
Original: apple banana cherry
Uppercase: APPLE BANANA CHERRY

Hash Keys Conversion

uc is useful for normalizing hash keys to uppercase.

hash.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.34.0;

my %config = (
    "timeout" => 30,
    "retries" => 3,
    "debug" => 0
);

my $key = "Timeout";
print "Value: ", $config{lc $key}, "\n";

# Convert all keys to uppercase
my %upper_config = map { uc $_ => $config{$_} } keys %config;
print join(", ", keys %upper_config), "\n";

This demonstrates converting hash keys to uppercase for case-insensitive lookups. We use both uc and lc for normalization.

$ ./hash.pl
Value: 30
TIMEOUT, RETRIES, DEBUG

File Processing

uc can standardize text when processing files.

file.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.34.0;

open(my $fh, '<', 'data.txt') or die "Can't open file: $!";

while (my $line = <$fh>) {
    chomp $line;
    print uc($line), "\n";
}

close($fh);

This script reads a file line by line, converts each line to uppercase, and prints it. Combining chomp and uc is common.

Unicode Handling

uc properly handles Unicode characters when using appropriate Perl versions and settings.

unicode.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.34.0;
use utf8;

my $text = "café résumé";
my $upper = uc($text);

binmode STDOUT, ':utf8';
print "Original: $text\n";
print "Uppercase: $upper\n";

With use utf8, Perl correctly handles non-ASCII characters. The output shows proper conversion of accented letters to uppercase.

$ ./unicode.pl
Original: café résumé
Uppercase: CAFÉ RÉSUMÉ

Best Practices

Preserve originals: Create new variables for uppercase versions.
Use locale: Enable locale for language-specific conversions.
Combine with lc: For case-insensitive comparisons.
Handle Unicode: Use utf8 pragma for non-ASCII text.
Document conversions: Make case changes obvious in code.

Source

Perl uc Documentation

This tutorial covered Perl's uc function with practical examples demonstrating its usage in various scenarios.

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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