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Full Discussion: grep regular expression
Top Forums Shell Programming and Scripting grep regular expression Post 302316934 by Calypso on Sunday 17th of May 2009 11:20:45 AM
Old 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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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)
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