Passing a variable to a sub process.

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

Monks, I've dealt with this before with no issues; I've tried a lot of different scenarios so I could try to get this particular issue resolved.

I am trying to pass $nossl to a subprocess in order for it to be handled. For some reason the variable ends up empty once I try to declare it inside of the subprocess.

if ($nossl) {
   &mkdirs($nossl);
}
[download]

sub mkdirs {


    # Can be used to build SSL and non-SSL sites.
my $nossl;
my $newsite = $nossl;

    if ( -e "/virtual/$newsite" ) {
        die "The site \"$newsite\"  must already be built!\n";
    }
    else {
        my %mkdircmd = (
            virtual   => "mkdir /virtual/$newsite",
            apachedir => "mkdir /etc/httpd/conf/$newsite",
            ssl_crt   => "mkdir /etc/httpd/conf/$newsite/ssl.crt",
            ssl_csr   => "mkdir /etc/httpd/conf/$newsite/ssl.csr",
            ssl_key   => "mkdir /etc/httpd/conf/$newsite/ssl.crt",
            logs      => "mkdir /var/log/httpd/$newsite"
        );

        system( $mkdircmd {'virtual'} );
        system( $mkdircmd {'apachedir'} );
        system( $mkdircmd {'ssl_crt'} );
        system( $mkdircmd {'ssl_csr'} );
        system( $mkdircmd {'ssl_key'} );
        system( $mkdircmd {'logs'} );
        sleep 2;
        print "Directories have been built!\n";
    }
}
[download]

Comment on Passing a variable to a sub process. Select or Download Code

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Re: Passing a variable to a sub process. by apl (Monsignor) on Apr 02, 2008 at 17:49 UTC
In your mkdirs subroutine, you should replace `my $nossl;` [download] with `my ( $nossl ) = @_;` [download] This indicates you want that variable to be populated with the value passed to the subroutine. If you called mkdirs with two parameters, your subroutine would need to say `my ( $nossl, $arg2 ) = @_;` [download] By the way, you're not calling a subprocess, you're calling a subroutine. A subprocess would be a program or command spawned from your program. A subroutine is a logical part of your program. One final note: for arcane reasons, you shouldn't put an ampersand in front of the name of the subroutine you're calling. I know the old Camel book did that, but don't. Revised: for clarity.	[reply] [d/l] [select]
Re: Passing a variable to a sub process. by toolic (Bishop) on Apr 02, 2008 at 17:50 UTC
Inside `sub mkdirs`, you are declaring a new vaiable, `$nossl`, which is local to the sub. It is different from the variable of the same name which resides in the calling scope. Perhaps what you want to do is: `#!/usr/bin/env perl use warnings; use strict; my $nossl = 'foo'; mkdirs($nossl); sub mkdirs { my $nossl = shift; print "nossl=$nossl\n"; }` [download] This prints: `nossl=foo` [download] Take a look at shift, perlsub and my.	[reply] [d/l] [select]
Re^2: Passing a variable to a sub process. by misconfiguration (Sexton) on Apr 02, 2008 at 18:21 UTC
I hope to someday be as wise as you two, the depth of understanding you have is quite amazing. After the string $nossl was passed into the subroutine I changed some things. `my $nossl = shift; my $newsite = $nossl;` [download] Thanks again for your help, I learned a lot from this lesson.	[reply] [d/l]
Re^3: Passing a variable to a sub process. by Bilbo (Pilgrim) on Apr 02, 2008 at 18:58 UTC
Since you never use $nossl within your routine, this is equivalent to `my $newsite = shift;` [download] There is no significance in using the same name inside and outside the routine. This just says that you want to set $newsite using the first parameter passed to the subroutine.	[reply] [d/l]
Re: Passing a variable to a sub process. by johngg (Canon) on Apr 02, 2008 at 21:56 UTC
A couple of points: You should omit the ampersand (`&`) from your subroutine call. You should check for the success or otherwise of the `mkdir` commands by looking at the return code from system. A non-zero return code would mean something went a bit wonky. It's nice to have faith but your `print` statement might be a bit optimistic. I hope this is of interest. Cheers, JohnGG	[reply] [d/l] [select]
Re: Passing a variable to a sub process. by mhearse (Chaplain) on Apr 02, 2008 at 18:43 UTC
You may find this node on scoping useful.	[reply]