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Full Discussion: Learning regular expressions
Top Forums UNIX for Dummies Questions & Answers Learning regular expressions Post 302894237 by Ditto on Monday 24th of March 2014 12:19:13 PM
Old 03-24-2014
Quote:
Originally Posted by jim mcnamara
FWIW -

egrep -v does an exclusionary search and using alternation try:

Code:
egrep -v  '( @[a-zA-Z0-9]|\.com )'  somefile

Just an opinion - sometimes really long one-liners are harder to debug. We see 250 character "one-liners" here frequently. They are hard to work with.
Understood .. I'm just curious to use this as a learning exercise.

hmm, that's cute, reverse logic. Clever.
Ok, it still pulls back a line with no @'s in it.
Trying this, however, still doesn't work ... hmmm

Code:
egrep -v  '([^@]| @[a-zA-Z0-9]|\.com )' test.txt

 

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Perl::Critic::Policy::RegularExpressions::RequireExtendeUsermContributed PPerl::Critic::Policy::RegularExpressions::RequireExtendedFormatting(3pm)

NAME
Perl::Critic::Policy::RegularExpressions::RequireExtendedFormatting - Always use the "/x" modifier with regular expressions. AFFILIATION
This Policy is part of the core Perl::Critic distribution. DESCRIPTION
Extended regular expression formatting allows you mix whitespace and comments into the pattern, thus making them much more readable. # Match a single-quoted string efficiently... m{'[^\']*(?:\.[^\']*)*'}; #Huh? # Same thing with extended format... m{ ' # an opening single quote [^\'] # any non-special chars (i.e. not backslash or single quote) (?: # then all of... \ . # any explicitly backslashed char [^\']* # followed by an non-special chars )* # ...repeated zero or more times ' # a closing single quote }x; CONFIGURATION
You might find that putting a "/x" on short regular expressions to be excessive. An exception can be made for them by setting "minimum_regex_length_to_complain_about" to the minimum match length you'll allow without a "/x". The length only counts the regular expression, not the braces or operators. [RegularExpressions::RequireExtendedFormatting] minimum_regex_length_to_complain_about = 5 $num =~ m<(d+)>; # ok, only 5 characters $num =~ m<d.(d+)>; # not ok, 9 characters This option defaults to 0. Because using "/x" on a regex which has whitespace in it can make it harder to read (you have to escape all that innocent whitespace), by default, you can have a regular expression that only contains whitespace and word characters without the modifier. If you want to restrict this, turn on the "strict" option. [RegularExpressions::RequireExtendedFormatting] strict = 1 $string =~ m/Basset hounds got long ears/; # no longer ok This option defaults to false. NOTES
For common regular expressions like e-mail addresses, phone numbers, dates, etc., have a look at the Regexp::Common module. Also, be cautions about slapping modifier flags onto existing regular expressions, as they can drastically alter their meaning. See <http://www.perlmonks.org/?node_id=484238> for an interesting discussion on the effects of blindly modifying regular expression flags. TO DO
Add an exemption for regular expressions that contain "Q" at the front and don't use "E" until the very end, if at all. AUTHOR
Jeffrey Ryan Thalhammer <jeff@imaginative-software.com> COPYRIGHT
Copyright (c) 2005-2011 Imaginative Software Systems. All 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 2012-0Perl::Critic::Policy::RegularExpressions::RequireExtendedFormatting(3pm)
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