Variable scoping problem

kwatts59 has asked for the wisdom of the Perl Monks concerning the following question:

Hello, If somebody could help me out with this variable scoping problem, it would be greatly appreciated.

Program a.pl

use strict;
use warnings;

our ($database);

$database = "test1";
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Program b.pl

use strict;
use warnings;

our ($database);

$database = "test2";
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Program c.pl

require "a.pl";
print "$database\n";
require "b.pl";
print "$database\n";
require "a.pl";
print "$database\n";
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The output from program c.pl is as follows:

test1
test2
test2
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I would like the output to be as follows:

test1
test2
test1
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What am I doing wrong?

Comment on Variable scoping problem Select or Download Code

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Re: Variable scoping problem by haukex (Archbishop) on Nov 25, 2019 at 22:25 UTC
require only loads each file once. Although there are workarounds (deleting from %INC, or do with additional error checking), I would recommend against the architecture you've shown in general. Perhaps if you could explain what the bigger picture is, we can suggest a better approach.	[reply]
Re: Variable scoping problem by hippo (Archbishop) on Nov 25, 2019 at 22:29 UTC
The second time you try to `require "a.pl";` has no effect because a.pl is already loaded. To ensure the other scripts are always executed by c.pl, use `do` instead of `require`. `do "a.pl"; print "$database\n"; do "b.pl"; print "$database\n"; do "a.pl"; print "$database\n";` [download]	[reply] [d/l] [select]
Re^2: Variable scoping problem by haukex (Archbishop) on Nov 25, 2019 at 22:50 UTC
use `do` instead of `require` Yes, but do requires additional error checking to make sure it actually worked (the docs show one example, that could be simplified a bit).	[reply] [d/l] [select]
Re^3: Variable scoping problem by kwatts59 (Novice) on Dec 04, 2019 at 14:45 UTC
Thank you. I replaced "require" with "do" and the program now works.	[reply]
Re: Variable scoping problem (how is my program running) by Anonymous Monk on Nov 26, 2019 at 00:35 UTC
I would like the output to be as follows: What am I doing wrong? Why would you like the output to be as follows? What are you actually trying to accomplish? Is this a test/quiz question? Or What book are you learning from? Have you read require? This is how you should write that program `my $database = LoadDatabase('a.pl'); print "$database\n"; $database = LoadDatabase('b.pl'); print "$database\n"; $database = LoadDatabase('a.pl'); print "$database\n"; exit( 0 ); sub LoadDatabase { .... }` [download] Devel::Trace will trace your program exactly `>> c.pl:1: require "a.pl"; >> a.pl:1: use strict; ... >> a.pl:2: use warnings; ... >> c.pl:2: print "$database\n"; >> c.pl:3: require "b.pl"; >> b.pl:1: use strict; ... >> b.pl:2: use warnings; ... >> c.pl:4: print "$database\n"; >> c.pl:5: require "a.pl"; >> c.pl:6: print "$database\n";` [download] As you can see the last require does't execute a.pl because its already loaded	[reply] [d/l] [select]
Re: Variable scoping problem by BillKSmith (Monsignor) on Nov 27, 2019 at 03:47 UTC
Note that your problem has nothing to do with "variable scoping". There is only one package variable named $database. Neither the variable nor its name ever go out of scope before the end of the program. The value of that variable changes when the required code is executed as other monks have explained. Bill	[reply]
Re: Variable scoping problem by Anonymous Monk on Nov 26, 2019 at 01:58 UTC
This is an "old PHP-style" coding technique that today is strongly discouraged even in PHP.	[reply]
Re^2: Variable scoping problem by Anonymous Monk on Nov 26, 2019 at 15:49 UTC
Citation, please.	[reply]