FAQ 4.21 How do I remove consecutive pairs of characters?

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4.21: How do I remove consecutive pairs of characters?

    (contributed by brian d foy)

    You can use the substitution operator to find pairs of characters (or
    runs of characters) and replace them with a single instance. In this
    substitution, we find a character in "(.)". The memory parentheses store
    the matched character in the back-reference "" and we use that to
    require that the same thing immediately follow it. We replace that part
    of the string with the character in $1.


    We can also use the transliteration operator, "tr///". In this example,
    the search list side of our "tr///" contains nothing, but the "c" option
    complements that so it contains everything. The replacement list also
    contains nothing, so the transliteration is almost a no-op since it
    won't do any replacements (or more exactly, replace the character with
    itself). However, the "s" option squashes duplicated and consecutive
    characters in the string so a character does not show up next to itself

            my $str = 'Haarlem';   # in the Netherlands
            $str =~ tr///cs;       # Now Harlem, like in New York


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