perl - passing values to subroutines

sporty · 08-07-2006, 12:38 PM

I am having some trouble understanding how to reference a value passed to a subroutine.

When I run the following code the first print statement in sub open_domain prints the value passed in from the sub open_states; however the second print statement in open_domain prints the same value as the $_ which was read from the file domain.list.
I'm confused, I thought the second print statement would print the value read in from the file domain.list and the value passed in from the sub open_states.

Could someone please explain to me why the @_ in the second print statement does not print the passed in value and how I correct this?
Thanks

Code:

#!/usr/bin/perl -w
sub open_domain {
     print "@_";
   open (DOM, "<", "domain.list");
        while (<DOM>) {
          print "$_",".","@_";
        }
   close DOM;
}   # end open_dom

sub open_states {
        open (STATES, "<", "abv.list");

        while (<STATES>) {
                open_dom ($_);
        } #end while STATES
        close STATES;
} # end sub open_states

open_states ();

spirit receiver · 08-07-2006, 01:44 PM

I guess you want something like this:

Code:

sub open_domain {
   my $arg = shift;
   print $arg;
   open (DOM, "<", "domain.list");
        while (<DOM>) {
          print "$_",".",$arg;
        }
   close DOM;
}   # end open_dom

sporty · 08-07-2006, 02:37 PM

Quote:

Originally Posted by spirit receiver

I guess you want something like this:

Code:

sub open_domain {
   my $arg = shift;
   print $arg;
   open (DOM, "<", "domain.list");
        while (<DOM>) {
          print "$_",".",$arg;
        }
   close DOM;
}   # end open_dom

Thanks spirit receiver. I guess from this code that the @_ is only good if you dont read anymore data from another file because then the array @_ is used inside the sub for the read- correct?

Thanks again

spirit receiver · 08-07-2006, 03:53 PM

Seems like you're asking a good question here, I couldn't reproduce your problem.

What does the following script return in your case?

Code:

#! /usr/bin/perl

use warnings;
use strict;

sub nuff {
  open( FILE, "< tempdata-$$");
  while (<FILE>) {
    print "$_","@_","\n";
   }
  close( FILE );
}

-e "tempdata-$$" && die;
open( DATA , "> tempdata-$$" );
print DATA "I am read from the file.\nSo am I.\nMe too.\n";
close( DATA );

my @array = ("arg 1,","arg 2,","arg 3");
nuff @array;
system "rm tempdata-$$";

This is what I get:

Code:

ada@barnabas:~/tmp> ./test.pl
I am read from the file.
arg 1,arg 2,arg 3
So am I.
arg 1,arg 2,arg 3
Me too.
arg 1,arg 2,arg 3

sporty · 08-07-2006, 05:30 PM

Quote:

Originally Posted by spirit receiver

This is what I get:

Code:

ada@barnabas:~/tmp> ./test.pl
I am read from the file.
arg 1,arg 2,arg 3
So am I.
arg 1,arg 2,arg 3
Me too.
arg 1,arg 2,arg 3

I got the same output as you running your code.

Code:

I am read from the file.
arg 1, arg 2, arg 3
So am I.
arg 1, arg 2, arg 3
Me too.
arg 1, arg 2, arg 3

The more I learn about perl the less I know.
Thanks again

spirit receiver · 08-07-2006, 06:27 PM

I tried your script, and I also got that strange behaviour. Note that @_ will even be uninitialized if accessed from open_domain after the inner loop.
The content of @_ seems to be somewhat undetermined in this situation, doesn't it?

bigearsbilly · 08-08-2006, 09:29 AM

got any example data files???

spirit receiver · 08-08-2006, 10:13 AM

The data is completely irrelevant, just create two files, domain.list and abv.list, each with a single line of text. There's a typo in sporty's script, the subroutine should be named open_dom instead of open_domain.