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Aug 11, 2012, 4:57 AM
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[perl #114452] [adi@hexapodia.org: Bug#681849: perl: regex negative lookbehind does not work before $]
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# New Ticket Created by Dominic Hargreaves
# Please include the string: [perl #114452]
# in the subject line of all future correspondence about this issue.
# <URL: https://rt.perl.org:443/rt3/Ticket/Display.html?id=114452 >
I can confirm that the behaviour is the same on current blead, so
forwarding here initially.
Thanks,
Dominic.
----- Forwarded message from Andy Isaacson <adi [at] hexapodia> -----
Date: Mon, 16 Jul 2012 23:06:05 -0700
From: Andy Isaacson <adi [at] hexapodia>
To: Debian Bug Tracking System <submit [at] bugs>
Subject: Bug#681849: perl: regex negative lookbehind does not work before $
Package: perl
Version: 5.14.2-6
Severity: normal
Dear Maintainer,
The negative look-behind assertion does not work correctly before $ (the
end-of-line assertion).
I expect to be able to say "match lines that do not end in bar"
using the regex /(?<!bar)$/ . However this does not work:
% (echo foo; echo bar; echo foobaz) | perl -ne 'print if(/(?<!bar)$/)'
foo
bar
foobaz
%
It should not have printed "bar" above.
A similar pattern using /^(?!bar)/ works to say "lines that do not
start with bar", and negative look-behind works before a string:
# negative lookahead
% (echo foo; echo bar; echo foobaz) | perl -ne 'print if(/^(?!foo)/)'
bar
%
# negative lookbehind before string
% (echo foo; echo bar; echo foobaz) | sed 's/$/x/g' | \
perl -ne 'print if(/(?<!bar)x$/)'
foox
foobazx
%
I found a workaround that may shed light on the root cause of the
problem. Normally /$/ matches the end of a string or the line-ending
character at the end of a <> string, and regex behavior with $ is not
changed by chomp()ing the line-ending-character away. But in this case,
there is a difference. If I "chomp;" before matching, the negative
look-behind assertion works correctly:
% (echo foo; echo bar; echo foobaz) | perl -ne 'chomp; print if(/(?<!bar)$/)'
foofoobaz
%
Note that it did not print "bar" above, correctly implementing the behavior
documented in perlre(1).
-- System Information:
Debian Release: wheezy/sid
APT prefers unstable
APT policy: (500, 'unstable'), (500, 'stable')
Architecture: amd64 (x86_64)
Kernel: Linux 3.4.0-rc4-00095-g95f7147 (SMP w/4 CPU cores)
Locale: LANG=en_US.utf8, LC_CTYPE=en_US.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Versions of packages perl depends on:
ii libbz2-1.0 1.0.6-1
ii libc6 2.13-26
ii libdb5.1 5.1.29-1
ii libgdbm3 1.8.3-10
ii perl-base 5.14.2-6
ii perl-modules 5.14.2-6
ii zlib1g 1:1.2.3.4.dfsg-3
Versions of packages perl recommends:
ii netbase 4.47
Versions of packages perl suggests:
ii libterm-readline-gnu-perl | libterm-readline-perl-perl <none>
ii make 3.81-8.1
ii perl-doc 5.14.2-6
-- no debconf information
----- End forwarded message -----
--
Dominic Hargreaves | http://www.larted.org.uk/~dom/
PGP key 5178E2A5 from the.earth.li (keyserver,web,email)
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