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

I have a sub that can fetch the network information of a host. The sub looks like this:

for my $nic (networkInfo()) {
      if (defined $nic->{ip}) {
            print ">>>  IP4 Device: $nic->{device} is using: $nic->{ip
+} address\n" .
        "\tMask: $nic->{mask}\n" .
        "\tBroadcast: $nic->{bcast}\n";
    }
    if (defined $nic->{ip6}) {
        print ">>>  IP6 Device: $nic->{device} is using: $nic->{ip6} a
+ddress\n";
    }
}

[download]

The print lines are working, note how the print uses a $nic->{} variable. Okay, so now I want to send 2 variables into a new sub. These two variables are

$platform and $nic->{device}

I have a new sub call that tries to do this but when I get into the subroutine code itself, I don't know how to access the 2nd variable $nic->{device}

Here is the code for my call and the sub so you can see what I am trying to do....

CALL

my @files = getPlatformFiles($platform, $nic->{device});
foreach my $file (@files) {
    print "$file\n";
}

[download]

SUB

sub getPlatformFiles {
    my $plat_in = shift;
    my @list;
    if ($plat_in =~ /RedHat/) {
        @list = ("/etc-test/resolv.conf", 
                  "/etc-test/sysconfig/network-scripts/ifcfg-$nic->{de
+vice}");
    }
    return @list;
}

[download]

When I run the code I get an message telling me the following: (ignore the line numbers please)

Global symbol "$nic" requires explicit package name at ./new.pl line 1
+85.
Execution of ./new.pl aborted due to compilation errors (#1)
    (F) You've said "use strict vars", which indicates that all variab
+les
    must either be lexically scoped (using "my"), declared beforehand 
+using
    "our", or explicitly qualified to say which package the global var
+iable
    is in (using "::").

Uncaught exception from user code:
        Global symbol "$nic" requires explicit package name at ./new.p
+l line 185.
Execution of ./new.pl aborted due to compilation errors.
 at ./new.pl line 189

[download]

Line 185 is the line in the sub itself with the  $nic->{device} variable

Replies are listed 'Best First'.
Re: Another scoping issue: How do I send 2 variables to my sub and use both.
by kennethk (Abbot) on Feb 05, 2010 at 16:34 UTC
    As detailed in DESCRIPTION in perlsub, variables passed into a subroutine are stored in the special @_ array. The shift at the start of your subroutine implicitly accesses this array. Since $nic is presumably a hash reference and thus a scalar, you could access it with: 

    sub getPlatformFiles {
    my $plat_in = shift;
    my $nic = shift;
    my @list;

    [download]

    A style I prefer when not using OO-style programming is to use an list assignment rather than a shift, but this is wholly subjective: 

    sub getPlatformFiles {
    my ($plat_in, $nic) = @_;
    my @list;

    [download]

    There are some potential complexities involved in scoping here, which may bite you if you are incautious and use the same variable names in a script and a subroutine. Note the following is for demonstration purposes and using this approach without good reason can result in some painful bug hunting. If you declare a variable with my in scoping using that contains a subroutine, that subroutine can see all variables in that scope, and hence the following works: 

    #!/usr/bin/perl
use strict;
use warnings;

my $variable = "Hello\n";
outputter();

sub outputter {
    print $variable;
}

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    This is because the scope of $variable is at the script level and contains the subroutine definition. On the other hand, the following will output an error message: 

    #!/usr/bin/perl
use strict;
use warnings;

sub outputter {
    print $variable;
}

my $variable = "Hello\n";
outputter();

    [download]
    because the variable is not declared prior to its use in the subroutine. These behaviors allow for some very powerful structures called closures.
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[d/l]
[select]

      I have tried it both ways and I am getting a message about "use of uninitialized value in concat......" 

      sub getPlatformFiles {
#    my ($plat_in, $nic_in) = @_;
    my $plat_in = shift;
    my $nic_in = shift;
    my @list;
    print "<$plat_in>\n";    #debugging
    print "<$nic_in>\n";    #debugging
    if ($plat_in =~ /RedHat/) {
        @list = ("/etc-test/resolv.conf", 
                  "/etc-test/sysconfig/network-scripts/ifcfg-$nic->{de
+vice}");
    }
    return @list;
}

      [download]

      The first debugging has the correct value but the second is blank empty. It prints <>

[reply]
[d/l]
[select]
        "/etc-test/sysconfig/network-scripts/ifcfg-$nic->{device}");

        should read

        "/etc-test/sysconfig/network-scripts/ifcfg-$nic_in->{device}");

        - you missed a search and replace. If you are using strict and it did not get caught, that would be for the reason I detailed before.

        If print "<$nic_in>\n"; is not outputting something that looks like <HASH(0x236e88)>, then you are passing it an undefined value. Are you calling the subroutine with something that looks like getPlatformFiles($platform,$nic);? Are you sure $nic is defined?

[reply]
[d/l]
[select]
Re: Another scoping issue: How do I send 2 variables to my sub and use both.
by starX (Chaplain) on Feb 05, 2010 at 16:29 UTC
    Highly untested, but try this: 
    sub getPlatformFiles {
    my $plat_in = shift;
    my $nic = shift;
    my @list;
    if ($plat_in =~ /RedHat/) {
        @list = ("/etc-test/resolv.conf", 
                  "/etc-test/sysconfig/network-scripts/ifcfg-$nic->{de
+vice}");
    }
    return @list;
}

    [download]
    You're passing in a list of two elements, so you need to shift the second one onto a more localized variable in order to access it within the subroutine.

    --starX
    www.axisoftime.com

[reply]
[d/l]
Re: Another scoping issue: How do I send 2 variables to my sub and use both.
by hexcoder (Curate) on Feb 06, 2010 at 13:05 UTC
    If you call it like this:

    my @files = getPlatformFiles($platform, $nic->{device});

    [download]
    your sub should look like this

    sub getPlatformFiles {
  my $plat_in = shift;
  my $nic_device_in = shift;
  my @list;
  if ($plat_in =~ /RedHat/) {
    @list = ("/etc-test/resolv.conf",
             "/etc-test/sysconfig/network-scripts/ifcfg-$nic_device_in
+");
  }
  return @list;
}

    [download]
[reply]
[d/l]
[select]

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