05-17-2009
grep regular expression
please can someone tell me what the following regrex means
grep "^aa*$" <file>
I thought this would match any word beginning with aa and ending with $, but it doesnt.
Thanks in advance
Calypso
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LEARN ABOUT DEBIAN
perl::critic::policy::builtinfunctions::prohibitbooleangrep
Perl::Critic::Policy::BuiltinFunctions::ProhibitBooleanGUser3Contributed Perl DocuPerl::Critic::Policy::BuiltinFunctions::ProhibitBooleanGrep(3pm)
NAME
Perl::Critic::Policy::BuiltinFunctions::ProhibitBooleanGrep - Use "List::MoreUtils::any" instead of "grep" in boolean context.
AFFILIATION
This Policy is part of the core Perl::Critic distribution.
DESCRIPTION
Using "grep" in boolean context is a common idiom for checking if any elements in a list match a condition. This works because boolean
context is a subset of scalar context, and grep returns the number of matches in scalar context. A non-zero number of matches means a
match.
But consider the case of a long array where the first element is a match. Boolean "grep" still checks all of the rest of the elements
needlessly. Instead, a better solution is to use the "any" function from List::MoreUtils, which short-circuits after the first successful
match to save time.
CONFIGURATION
This Policy is not configurable except for the standard options.
CAVEATS
The algorithm for detecting boolean context takes a LOT of shortcuts. There are lots of known false negatives. But, I was conservative in
writing this, so I hope there are no false positives.
AUTHOR
Chris Dolan <cdolan@cpan.org>
CREDITS
Initial development of this policy was supported by a grant from the Perl Foundation.
COPYRIGHT
Copyright (c) 2007-2011 Chris Dolan. Many rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. The full text of this license
can be found in the LICENSE file included with this module.
perl v5.14.2 2012-06-07 Perl::Critic::Policy::BuiltinFunctions::ProhibitBooleanGrep(3pm)