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Full Discussion: Korn expr substr fails for non-numeric value
Top Forums Shell Programming and Scripting Korn expr substr fails for non-numeric value Post 302382816 by bakunin on Friday 25th of December 2009 11:55:00 PM
Old 12-26-2009
In AIX (including 5.3) /bin/ksh is a ksh88, whereas /bin/ksh93 is a ksh93. The substr()-function in the form "${var:start:length}" is only implemented in ksh93.

cfajohnsons observation is correct in a very general way: using ksh93-functions always runs the risk of getting less portable. On the other hand: using an external tool (expr, sed, awk, whatever) to trim the variables content is expensive in terms of system calls. I would like to offer the following solution to this problem, which which work in every ksh.version:

Code:
sub1=${DDNAME%${DDNAME#?????}}
sub=${sub1#???}

The first line extracts the first 5 characters from the string $DDNAME, the second statement extracts the last 2 from these 5 characters, effectively giving the substring starting at pos 4, length 2. Because this is done completely in the shell and without calling an external program it shoulld be by far faster than any solution based on such a program.

cfajohnson already explained how this can be tested for being an integer or not.

I hope this helps.

bakunin
 

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LEARN ABOUT CENTOS

perl::critic::policy::builtinfunctions::prohibitlvaluesubstr

Perl::Critic::Policy::BuiltinFunctions::ProhibitLvalueSuUser(Contributed Perl DocumPerl::Critic::Policy::BuiltinFunctions::ProhibitLvalueSubstr(3)

NAME

       Perl::Critic::Policy::BuiltinFunctions::ProhibitLvalueSubstr - Use 4-argument "substr" instead of writing "substr($foo, 2, 6) = $bar".

AFFILIATION

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

DESCRIPTION

       Conway discourages the use of "substr()" as an lvalue, instead recommending that the 4-argument version of "substr()" be used instead.

	   substr($something, 1, 2) = $newvalue;     # not ok
	   substr($something, 1, 2, $newvalue);      # ok

       The four-argument form of "substr()" was introduced in Perl 5.005.  This policy does not report violations on code which explicitly
       specifies an earlier version of Perl (e.g. "use 5.004;").

CONFIGURATION

       This Policy is not configurable except for the standard options.

SEE ALSO

       "substr" in perlfunc (or "perldoc -f substr").

       "4th argument to substr" in perl5005delta

AUTHOR

       Graham TerMarsch <graham@howlingfrog.com>

COPYRIGHT

       Copyright (c) 2005-2011 Graham TerMarsch.  All rights reserved.

       This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.16.3							    2014-06-09	   Perl::Critic::Policy::BuiltinFunctions::ProhibitLvalueSubstr(3)
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