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Top Forums Shell Programming and Scripting Resolve variable inside another variable Post 302684539 by Corona688 on Thursday 9th of August 2012 05:25:55 PM
Old 08-09-2012
You either can't or won't tell me what the purpose of your program is. Nobody writes a program to "substitute in a variable", presumably that program has some actual use to you.

Fine, I'll do what I can without it.

You are doing it exactly backwards, which is why you are having so many problems. Set the variables first. Then make your query, letting it substitute the variables right then and there. That is the way variables are supposed to work. You'll get exactly what you want, quotes intact.

If possible, use it directly instead of storing it in a variable -- 30 lines is a lot to put in one variable, and you want to avoid splitting and accidental substitution anyway. You can use a here-document to stream something into a program, variables will substitute inside it:

Code:
databaseprogram <<EOF
Select '$ENV',t1.field1,t2.field2
        from $table1 t1,$table2 t2
        where t1.field1='$var1'
        and t2.field1='$var2'
EOF


Last edited by Corona688; 08-09-2012 at 06:49 PM..
 

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XS(3)							User Contributed Perl Documentation						     XS(3)

NAME
Readonly::XS - Companion module for Readonly.pm, to speed up read-only scalar variables. VERSION
This document describes version 1.05 of Readonly::XS, February 24, 2009. SYNOPSIS
Install this module, but do not use it. DESCRIPTION
The Readonly module (q.v.) is an effective way to create non-modifiable variables. However, it's relatively slow. The reason it's slow is that is implements the read-only-ness of variables via tied objects. This mechanism is inherently slow. Perl simply has to do a lot of work under the hood to make tied variables work. This module corrects the speed problem, at least with respect to scalar variables. When Readonly::XS is installed, Readonly uses it to access the internals of scalar variables. Instead of creating a scalar variable object and tying it, Readonly simply flips the SvREADONLY bit in the scalar's FLAGS structure. Readonly arrays and hashes are not sped up by this, since the SvREADONLY flag only works for scalars. Arrays and hashes always use the tie interface. Why implement this as a separate module? Because not everyone can use XS. Not everyone has a C compiler. Also, installations with a statically-linked perl may not want to recompile their perl binary just for this module. Rather than render Readonly.pm useless for these people, the XS portion was put into a separate module. Programs that you write do not need to know whether Readonly::XS is installed or not. They should just "use Readonly" and let Readonly worry about whether or not it can use XS. If the Readonly::XS is present, Readonly will be faster. If not, it won't. Either way, it will still work, and your code will not have to change. Your program can check whether Readonly.pm is using XS or not by examining the $Readonly::XSokay variable. It will be true if the XS module was found and is being used. Please do not change this variable. EXPORTS None. SEE ALSO
Readonly.pm AUTHOR
/ COPYRIGHT Eric Roode, roode@cpan.org Copyright (c) 2003-2009 by Eric J. Roode. All Rights Reserved. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. To avoid my spam filter, please include "Perl", "module", or this module's name in the message's subject line, and/or GPG-sign your message. perl v5.16.3 2009-02-24 XS(3)
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