FAQ 4.21 How do I remove consecutive pairs of characters?

Discussion in 'Perl Misc' started by PerlFAQ Server, Jan 14, 2011.

  1. This is an excerpt from the latest version perlfaq4.pod, which
    comes with the standard Perl distribution. These postings aim to
    reduce the number of repeated questions as well as allow the community
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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 "\g1" 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.

    s/(.)\g1/$1/g;

    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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    PerlFAQ Server, Jan 14, 2011
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