Course of Raku / Regexes and grammars / Regexes / Substitution and replacement

Transliteration

When you want to replace individual characters rather than a whole pattern, use the transliteration operator tr///. It maps each character in the first set to the character in the same position of the second set:

my $s = 'hello';
$s ~~ tr/a..z/A..Z/;
say $s; # HELLO

Every lowercase letter is replaced by the uppercase letter at the matching position in the second range, so the whole word is upper-cased.

The two sets are matched up character by character. A small example that shifts three letters:

my $s = 'abcabc';
$s ~~ tr/abc/xyz/;
say $s; # xyzxyz

Here every a becomes x, every b becomes y, and every c becomes z.

Transliteration is the right tool for character-level mappings — changing case, swapping a small alphabet, or encoding. For anything that depends on a pattern rather than single characters, use s///.

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