Raku Books / Using Raku / Regexes and Grammars / Substitutions with regexes

76. Double each character

In a given string, double each alphanumeric character and print the result. Punctuation and spaces should stay untouched.

Regexes are very powerful tools for searching and replacing texts. In this task, only the alphanumeric characters are requested to be doubled. The \w character class is the perfect match to find these characters.

my $string = 'Hello, 1 World!';
$string ~~ s:g/(\w)/$0$0/;
say $string;

We are using the s/// construct here. The $string is matched against the \w regex. The parentheses around \w capture the found character. It is now contained in the $0 special variable.

In the second part of the replacement, $0 is used twice, and, thus, the doubled character is replacing the single character found in the string. The :g adverb makes the replacement global.

The program prints the following output:

HHeelllloo, 11 WWoorrlldd!

Let us update the program to exclude the r letter from the process. In other words, all the characters, except r, must be doubled. Build a new character class as a difference between \w and r as demonstrated in the following line of code:

$string ~~ s:g/(<[\w] - [r]>)/$0$0/;

Now, the output is a bit different: HHeelllloo, 11 WWoorldd!

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