Where to declare?

Rich36 has asked for the wisdom of the Perl Monks concerning the following question:

Part of the piece of code I'm working on involves getting a list of valid directories from the user. The problem that I'm having is this...
The code below works, but I get a error message stating.

Variable "@dirlist" will not stay shared at test.pl line 17.
Variable "@dirlist" will not stay shared at test.pl line 24.
[download]

Where/how do I declare that variable to avoid that warning? If I place the "my @dirlist" within the "getAns()" sub, it redeclares the variable and erases any information that was added. If I leave it out of that sub, I get that warning.

#!/usr/bin/perl -w

use strict;

my @dirs = &getDirs();

sub getDirs() {

    my @dirlist; # PROBLEM!!!
    sub getAns() {
        print qq(Enter a valid directory: );
        chomp(my $ans = <STDIN>);
        if ($ans ne "") {
            if ($ans =~ m/foo/g) {
                push(@dirlist, $ans);
                &getAns;
            } else {
                print qq(That is not a valid directory!\n);
                &getAns;
                }
            } else {
                return @dirlist;
            }
        }
    }

    my @dirs = &getAns();
    
    if (@dirs) {
        return @dirs;
    } else {
        die qq(No directories have been entered!\n);
    }

}
[download]

Thanks in advance for the help,
Rich36

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Re: Where to declare? by Masem (Monsignor) on Oct 24, 2001 at 21:58 UTC
Not the specific answer to your problem, but do you really need a nested sub for this application? A while loop is much much easier to build around than this. KISS. eg: `my @dirlist; print qq(Enter a valid directory); chomp (my $ans = <STDIN>); while ( $ans ne "" ) { if ( $ans =~ m/foo/g ) { push @dirlist, $ans; } else { print qq(That is not a valid dir); } print qq(Enter a valid directory); chomp ($ans = <STDIN>); } # @dirlist is now filled happily` [download] ----------------------------------------------------- Dr. Michael K. Neylon - mneylon-pm@masemware.com \|\| "You've left the lens cap of your mind on again, Pinky" - The Brain "I can see my house from here!" It's not what you know, but knowing how to find it if you don't know that's important	[reply] [d/l]
Re: Re: Where to declare? by traveler (Parson) on Oct 24, 2001 at 23:11 UTC
As an aside to your suggestion, I remember a programming course that taught recursion before loops and then taught while loops as an alternative to the "more natural" tail recursion. Interesting what some consider "simple". --traveler	[reply]
Re: Where to declare? by blackmateria (Chaplain) on Oct 24, 2001 at 22:02 UTC
Move the declaration of `@dirlist` after the nested sub (getAns), then pass it in as a hard reference: `sub getDirs() { sub getAns() { my ($dirlist) = @_; # new print qq(Enter a valid directory: ); chomp(my $ans = <STDIN>); if ($ans ne "") { if ($ans =~ m/foo/g) { push(@$dirlist, $ans); # note the @$dirlist &getAns; } else { print qq(That is not a valid directory!\n); &getAns; } } else { return @$dirlist; # note the @$dirlist } } my @dirlist; my @dirs = getAns(\@dirlist); # note the \@dirlist if (@dirs) { return @dirs; } else { die qq(No directories have been entered!\n); } }` [download] For more information on hard references, take a look at perlref. Just a stylistic note, you don't need to put the & on getAns to call if if you're already using () (the original has a line which read `my @dirs = &getAns()`). As a matter of fact, you should stay away from using & to call subroutines unless you understand how it's different from calling them with (). Calling with & makes @_ in the called subroutine an alias for @_ in the caller; () makes a copy instead. So changing the parameters in the subroutine could affect the variables used in the main program. This is probably not what you expect! Be careful. If I were you, I'd change the places in your code that call &getAns to getAns(). Anyway, hope this helps.	[reply] [d/l] [select]
Re: Where to declare? by Rich36 (Chaplain) on Oct 24, 2001 at 22:25 UTC
Thanks very much for your help. The "while" loop definitely simplified things. And this - As a matter of fact, you should stay away from using & to call subroutines unless you understand how it's different from calling them with (). Calling with & makes @_ in the called subroutine an alias for @_ in the caller; () makes a copy instead. So changing the parameters in the subroutine could affect the variables used in the main program. This is probably not what you expect! Be careful. - is definitely information I can use. I tend to be pretty liberal about using both "&" and "()" in my subroutine calls. I didn't realize there was a difference. Thanks for the help and enlightenment... Rich36	[reply]
(tye)Re: Where to declare? by tye (Sage) on Oct 24, 2001 at 23:36 UTC
Actually, that bit of text you quoted is incorrect. Using & without () does what is described. Using both together is probably a good practice, especially if you aren't in the habit of giving your subroutines names with mixed case. See (tye)Re: A question of style for more info. - tye (but my friends call me "Tye")	[reply]