How do I pass a variable through multiple subroutines in perl?

Question

I have a variable currentUser in a sub routine. It carries through to one subroutine, but does not carry through to another subroutine. How can I pass a variable through multiple subroutines while keeping the value?

sub login {
    &app_header;
    print <<EOF;
<form name="macform" method="POST" enctype="application/x-www-form-urlencoded"       action="$fullurl">
    ...stuff
    EOF  
}

sub html_menu {
    $me = $currentUser;
    print $me;
    print <<EOF;
    <form name="menuform" method="POST" enctype="application/x-www-form-urlencoded"     action="$fullurl">
    ..stuff
    EOF
    &app_list_button;
    print "<br>";
    &app_search_button;
    print "<br>";
    &app_edit_button;
    print "</div>";
}

When I attempt to do the same thing the html_form sub does with currentUser in a new sub called after html_form), the variable does not display as what the user entered during login.

This would be a better question if you would include a short code snippet showing what you are trying to do and what you expect to happen. — mob, Nov 12 '12 at 17:08
Show the html_form sub as well... you don't have to include anything not related to the variable. — TLP, Nov 12 '12 at 17:20
I stand corrected. The code snippet and explanation are not making this a better question. — mob, Nov 12 '12 at 18:17

TLP · Accepted Answer · 2012-11-12T17:18:12.710

3

sub first {
    my $currentUser = shift;
    second($currentUser);
}

sub second {
    my $currentUser = shift;
    third($currentUser);
}

...and so on.

Passing a variable as argument is done through the @_ variable. You should not attempt to use global variables, it is not a good way to do it. You can do it like so:

my ($arg1, $arg2, @rest) = @_;

Or by using shift, pop and the other methods of manipulating arrays, like I above used shift.

If you are not already doing so, I recommend very strongly that you use

use strict;
use warnings;

It will help you solve many simple problems.

edited Nov 12 '12 at 17:18

answered Nov 12 '12 at 17:11

TLP

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This worked perfectly for me. Thanks for the help! Pardon my perl stupidity. – RichDiet Nov 12 '12 at 18:27
@user1703986 You're welcome. You should only call subs with the `name($arg)` method, unless you explicitly are trying to achieve something different, which is described in perldoc perlsub. – TLP Nov 12 '12 at 18:44

score 2 · Answer 2 · answered Nov 12 '12 at 17:08

2

The safest way is to use the variable as an argument:

sub r1 {
    my $arg = shift;
    r2($arg);
}

sub r2 {
    my $arg = shift;
    print "$arg in r2\n";
}

answered Nov 12 '12 at 17:08

choroba

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score 1 · Answer 3 · answered Nov 12 '12 at 17:55

When I attempt to do the same thing the html_form sub does with currentUser in a new sub called after html_form), the variable does not display as what the user entered during login.

Firstly, this is a rather complex example. You should have tried to break it down. To add to what others have said thus far, I'm going to tell you the & prefix on a subroutine's name without adding () changes the meaning. You use this in your examples, and I'm not sure if you know what it does. All of these have slightly different meanings.

foo() This simply calls sub foo with no arguments.
&foo This calls foo passing in @_ implicitly. Important note, if foo modifies @_ by reference then the @_ will change for the callee too.
&foo() This is just a relic of perl4. This calls foo with the explicit subref sigil. This is deprecated in all contexts.

there are also minor differences with prototypes and the & sigil that are outside of the bounds of the question

For more information see perldoc -q "calling a function" and perldoc perlsub

How do I pass a variable through multiple subroutines in perl?

3 Answers3