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From: lwall@jpl-devvax.jpl.nasa.gov (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: RLE compression in perl
Message-ID: <1991Jun25.170245.3867@jpl-devvax.jpl.nasa.gov>
Date: 25 Jun 91 17:02:45 GMT
References: <1991Jun24.203454.20218@com50.c2s.mn.org>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 24

In article <1991Jun24.203454.20218@com50.c2s.mn.org> caa@com50.c2s.mn.org (Charles Anderson) writes:
: 
: I'm trying to get perl to a simple form of RLE compression with the
: substitution operator like this:
: #!/usr/local/bin/perl
: open(TXT, '> test.txt');
: while (<>) {
:   ($buf = $_) =~ s/(.)\1{2,126}/sprintf("%c%c", length($&) + 128, $1)/ge;
:   print TXT $buf;
: }
: close(TXT);
: 
: I want to match any character then match 2 or more of the same character
: and replace it with the length of the matched string with the high bit
: set and the matched character.....to which perl tells me this:
: 
: /(.)\1{2,126}/: internal regexp foulup at rle.pl line 4, <> line 1.
: 
: Is this a bug or am I doing something wrong???

It's a bug.  I hope to fix it "right" (meaning "efficiently") in the next
patch, but as a (rather slow) workaround, you can put parens around the \1.

Larry