Webmaster Forum / Perl / Getting Started / March 2009

How can I retrieve data loaded into an array within a foreach block?
The array is defined outside the foreach block and is not the indexing
array of the foreach loop.

I have defined three arrays

my @lines = ();
my @line = ();
my @lastnames = ();

loaded into @lines a file in which each line is a series of tab
separated items and run the following code using warnings and strict

foreach (@lines) {
    @line = split /\t/, $_;
    push @lastnames, $line[2];
}

This works perfectly BUT when I try to uses @lastnames I get a warning
that it is undefined.  Specifically, I continued

@lastnames = sort @lastnames;

my $dup = "";
foreach (@lastnames) {
    if ($dup ne $_) {
        print $_;
        $dup = $_;
    }
}

and still everything works but there is a warning the $_ is undefined in
the condition statement.

I don't understand why it should not be possible to modify a global
variable inside the foreach loop.  In the second part of the problem I
modified the code as follows

my $dup = "";
my $item = "NoName";
foreach (@lastnames) {
    $item = $_;
    if ($dup ne $item) {
        print $item;
        $dup = $item;
    }
}

reasoning that foreach might be treating $_ like a numeral though it
actually holds current name from the array @lastnames. Now I received a
warning that $item was undefined in the conditional statement.

I hope there is a straightforward way of correctly doing what this code
does and I realy would like to understand why it is incorrect.  

Tom