l33t has asked for the wisdom of the Perl Monks concerning the following question:

I need some advice and help here. I am trying to print name of the input argument inside a sub routine.snippet of my code: 
my $var = 10;
sub print_name{
*glob = \$_[0];
print "Name of the variable ".*{glob}{NAME}."\n";
}
print_name $var;

Output: glob
Expected output: var

[download]
Is it possible to get name of scalar in Perl or is it only for Typeglob.

Replies are listed 'Best First'.
Re: To print name of a scalar
by syphilis (Archbishop) on Dec 18, 2010 at 06:50 UTC
    This will work: 
    use warnings;
use PadWalker qw(var_name);;

my $var = 10;
print_name(\$var);

sub print_name {
    print var_name(1, shift);
}

    [download]
    However, according to the PadWalker docs, it works only if $var is a "my" variable.

    Cheers,
    Rob
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[d/l]
Re: To print name of a scalar
by davido (Cardinal) on Dec 18, 2010 at 12:18 UTC

    Lexicals ('my' variables) aren't in the global symbol table. They don't appear in the %:: special variable's structure either (for the same reason). If it were a global via our, use vars, or non-adherence to use strict, then it does show up in the global symbol table, and can be referenced through %::. But even that is a little awkward. You don't really know by snooping in %:: when or where the variable first shows up in the script.

    I'm not sure what you're after, but could you use a tied scalar so that you're able to create a class of scalar that knows its name by object method?


    Dave

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[d/l]
[select]
      I was just experimenting reading perlsub. got stuck so wanted to know more. Thank you.
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Re: To print name of a scalar
by JavaFan (Canon) on Dec 18, 2010 at 14:02 UTC
    I am trying to print name of the input argument inside a sub routine
    What if the input argument doesn't have a name? What do you expect the answer to be in the following cases: 
    @foo = (10); sub bar {10}; $baz = 5; $qux = 2; @quux = (); $fred = 100
+;
print_name 10;
print_name \10;
print_name ${\10};
print_name [10];
print_name @foo;
print_name $foo[0];
print_name bar;
print_name $baz * $qux;
print_name;
print_name undef;
print_name @quux;
print_name sqrt $fred;
print_name do {my $waldo = 10};
print_name sub {10}->();

    [download]
[reply]
[d/l]
      I am a newbie in Perl. My assumption while doing this experiment was that, subroutine will be passed a scalar variable declared as my. example: 
      my $var; print_name $var;

      [download]
      Your question made me realize all possible scenario which I had totally forgotten about. Thank you. Will work towards it.
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[d/l]

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