in reply to printing lists...

You don't know the last element ... but you know the first. Using that knowledge, you can enhance your logic as follows:

my $first = 0;                         # a flag to remember the first 
+element

while(elements to check) {             # *
  if (elem should be printed) {        # *

     if ($first == 0) { $first = 1; }  # don't print a comma before th
+e first element
     else             { print ",";  }  # print a comma

     print elem                        # *
  }
}

[download]

HTH, Rata

Update: marked the pseudocode of the original poster with # * to reduce confusion

Replies are listed 'Best First'.
Re^2: printing lists...
by ww (Archbishop) on Jul 27, 2010 at 11:54 UTC
    Clever approach. Minor glitch in implementation.
    Update: that should be "glitch in my interpretation." Neither Ratazong's nor OP's data is necessarsarily formatted as I did it.

    my $first=0;

while (<DATA>) {
    chomp ($_);
    my $element = $_;
    if ($first == 0) { 
        $first = 1;   # don't print a comma before the first element
    } else {
         print ",";    # print a comma
    }
     print $element;
}

print "\n";

__DATA__
foo
bar
blivitz
this is a line
1
2
a
b
cde

    [download]

    Ratazzong produces:

    foo
,bar
,blivitz
,this is a line
,1
,2
,a
,b
,cde

    [download]

    instead of (what I understand to be) OP's desire:

    foo,bar,blivitz,this is a line,1,2,a,b,cde
[reply]
[d/l]
[select]

In Section Seekers of Perl Wisdom