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Full Discussion: perl - variable inheritance
Top Forums Shell Programming and Scripting perl - variable inheritance Post 302069603 by cbkihong on Monday 27th of March 2006 08:51:39 PM
Old 03-27-2006
That depends on what you mean by "parent" and "child" scripts.

If a Perl script invoked another Perl script through a shell with backticks, or system() for instance, then of course you can't. Even variables will not work as they are separate processes. Only some sort of IPC or command-line arguments will work. Probably you are not asking for this, but as a "parent" and "child" relationship, this seems to fit the terminology.

The Perl require() doesn't really have much a parent or child relationship. It just means to load and execute the code in an external file, but the execution environment is just exactly the same one.

Code:
~# cat a.pl
$a = 6;
require 'b.pl';

~# cat b.pl
print $a, "\n";

~# perl a.pl
6

Because $a is a package global (in package "main" here), its value is retained throughout the entire script unless its value is modified. Scoping has no effect, so you can always refer to it anywhere in the script.

But this won't work because my imposes lexical scope:

Code:
# cat a.pl
my $a = 6;
require 'b.pl';

# cat b.pl
print $a, "\n";

# perl -w a.pl
Use of uninitialized value in print at b.pl line 1.

local() is okay, though, because it has a dynamic scope. Slightly better than unrestricted package global:


Code:
# cat a.pl
local $a = 6;
require 'b.pl';

# cat b.pl
print $a, "\n";

# perl -w a.pl
6

There's nothing wrong with passing parameters around. In fact, it is usually a bad idea to use package globals unless you have established different packages (namespaces) to avoid variable name clashes.

Or you can use OOP. Then you probably can put everything into the object so that you only have one thing to pass around.
 

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LEARN ABOUT DEBIAN

test::script

Test::Script(3pm)					User Contributed Perl Documentation					 Test::Script(3pm)

NAME

       Test::Script - Basic cross-platform tests for scripts

DESCRIPTION

       The intent of this module is to provide a series of basic tests for 80% of the testing you will need to do for scripts in the script (or
       bin as is also commonly used) paths of your Perl distribution.

       Further, it aims to provide this functionality with perfect platform-compatibility, and in a way that is as unobtrusive as possible.

       That is, if the program works on a platform, then Test::Script should always work on that platform as well. Anything less than 100% is
       considered unacceptable.

       In doing so, it is hoped that Test::Script can become a module that you can safely make a dependency of all your modules, without risking
       that your module won't on some platform because of the dependency.

       Where a clash exists between wanting more functionality and maintaining platform safety, this module will err on the side of platform
       safety.

FUNCTIONS

   script_compiles
	   script_compiles( 'script/foo.pl', 'Main script compiles' );

       The "script_compiles" test calls the script with "perl -c script.pl", and checks that it returns without error.

       The path it should be passed is a relative unix-format script name. This will be localised when running "perl -c" and if the test fails the
       local name used will be shown in the diagnostic output.

       Note also that the test will be run with the same perl interpreter that is running the test script (and not with the default system perl).
       This will also be shown in the diagnostic output on failure.

   script_runs
	   script_runs( 'script/foo.pl', 'Main script runs' );

       The "script_runs" test executes the script with "perl script.pl" and checks that it returns success.

       The path it should be passed is a relative unix-format script name. This will be localised when running "perl -c" and if the test fails the
       local name used will be shown in the diagnostic output.

       The test will be run with the same perl interpreter that is running the test script (and not with the default system perl). This will also
       be shown in the diagnostic output on failure.

SUPPORT

       All bugs should be filed via the bug tracker at

       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Test-Script>

       For other issues, or commercial enhancement and support, contact the author.

AUTHOR

       Adam Kennedy <adamk@cpan.org>

SEE ALSO

       prove, <http://ali.as/>

COPYRIGHT

       Copyright 2006 - 2009 Adam Kennedy.

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

       The full text of the license can be found in the LICENSE file included with this module.

perl v5.10.1							    2009-11-24							 Test::Script(3pm)
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