You can use a backreference to obtain a single regex: 
    #!/usr/bin/perl -wl

    use strict;


    my $s = 'aaaabababbbbaaaccccbbbbbbaadddd';

    print $s;

    $s =~ s/((.)\2+)/length($1) . $2/eg;

    print $s;


    __END__
    Prints:
    aaaabababbbbaaaccccbbbbbbaadddd
    4ababa4b3a4c6b2a4d

[download]

--
John.

In reply to Re: Regexp: can I do it in one go? by jmcnamara
in thread Regexp: can I do it in one go? by moxliukas

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