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Full Discussion: sed using variables
Top Forums UNIX for Dummies Questions & Answers sed using variables Post 302256471 by vino on Sunday 9th of November 2008 11:57:57 PM
Old 11-10-2008
Quote:
Originally Posted by sivakumar.rj
Is there any differences between ' single quote and " double quotes....can u explain it in detail........
See man bash under the section Quoting
Code:
       Enclosing characters in single quotes preserves the literal value of each character within
       the quotes.  A single quote may not occur between single quotes, even when preceded  by  a
       backslash.

       Enclosing characters in double quotes preserves the literal value of all characters within
       the quotes, with the exception of $, ?, and \.  The characters $ and ? retain  their  spe-
       cial  meaning  within  double quotes.  The backslash retains its special meaning only when
       followed by one of the following characters: $, ?, ", \, or <newline>.  A double quote may
       be  quoted within double quotes by preceding it with a backslash.  When command history is
       being used, the double quote may not be used to quote the history expansion character.

 

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LEARN ABOUT CENTOS

perl::critic::policy::valuesandexpressions::prohibitquotesasquot

Perl::Critic::Policy::ValuesAndExpressions::ProhibitQuotPerl::Critic::Policy::ValuesAndExpressions::ProhibitQuotesAsQuotelikeOperatorDelimiters(3)

NAME

       Perl::Critic::Policy::ValuesAndExpressions::ProhibitQuotesAsQuotelikeOperatorDelimiters - Don't use quotes ("'", """, "`") as delimiters
       for the quote-like operators.

AFFILIATION

       This Policy is part of the core Perl::Critic distribution.

DESCRIPTION

       With the obvious exception of using single-quotes to prevent interpolation, using quotes with the quote-like operators kind of defeats the
       purpose of them and produces obfuscated code, causing problems for future maintainers and their editors/IDEs.

	   $x = q"q";		     #not ok
	   $x = q'q';		     #not ok
	   $x = q`q`;		     #not ok

	   $x = qq"q";		     #not ok
	   $x = qr"r";		     #not ok
	   $x = qw"w";		     #not ok

	   $x = qx`date`;	     #not ok

	   $x =~ m"m";		     #not ok
	   $x =~ s"s"x";	     #not ok
	   $x =~ tr"t"r";	     #not ok
	   $x =~ y"x"y";	     #not ok

	   $x =~ m'$x'; 	     #ok
	   $x =~ s'$x'y';	     #ok
	   $x = qr'$x'm;	     #ok
	   $x = qx'finger foo@bar';  #ok

CONFIGURATION

       This policy has three options: "single_quote_allowed_operators", "double_quote_allowed_operators", and "back_quote_allowed_operators",
       which control which operators are allowed to use each of "'", """, "`" as delimiters, respectively.

       The values allowed for these options are a whitespace delimited selection of the "m", "q", "qq", "qr", "qw", "qx", "s", "tr", and "y"
       operators.

       By default, double quotes and back quotes (backticks) are not allowed as delimiters for any operators and single quotes are allowed as
       delimiters for the "m", "qr", "qx", and "s" operators.  These defaults are equivalent to having the following in your .perlcriticrc:

	   [ValuesAndExpressions::ProhibitQuotesAsQuotelikeOperatorDelimiters]
	   single_quote_allowed_operators = m s qr qx
	   double_quote_allowed_operators =
	   back_quote_allowed_operators =

SUGGESTED BY

       Michael Schwern

AUTHOR

       Elliot Shank "<perl@galumph.com>"

COPYRIGHT

       Copyright (c) 2007-2011 Elliot Shank.

       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 v5.16.3						Perl::Critic::Policy::ValuesAndExpressions::ProhibitQuotesAsQuotelikeOperatorDelimiters(3)
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