Perl uc Function

last modified October 8, 2026

The Perl uc function converts all characters in a string to uppercase. It's a built-in string function. For character strings, it applies Unicode case rules.

uc returns a new string and doesn't modify the original. To change a variable itself, assign the result back to it.

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

With use locale, uc respects the current locale for byte strings. Character strings always follow Unicode rules.

locale.pl

#!/usr/bin/perl

use strict;
use warnings;
use v5.34.0;
use utf8;
use locale;
binmode STDOUT, ':encoding(UTF-8)';

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

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

With a decoded (use utf8) string, uc follows Unicode rules, and the German ß becomes SS whatever the locale. Byte strings, by contrast, depend on the system locale.

$ ./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 $_ => $config{$_} } sort keys %config;
print join(", ", sort 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
DEBUG, RETRIES, TIMEOUT

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.
Prefer Unicode strings: Decode input and use utf8 rather than relying on locale.
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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