There are so many ways to construct a loop. I'm not talking about syntax, i'm talking about the logic behind it and what the loop is trying to achieve. And even in a for() loop you might have some conditions that terminate the loop early (or restart the iterator).

For example, imagine a simple software that wants to run 100 loops of sending some data over the network. If the connection breaks, you'll have to restart from the beginning, or in some cases abort altogether. Let's write a small simulation:

#!/usr/bin/env perl

use strict;
use warnings;

my $restartcount = 0;
my $done = 1;
for(my $i = 0; $i < 100; $i ++) {

    # Do your complex stuff here
    print "$i\n";

    # Simulate some kind of random error
    # that requires a restart of the loop
    if(int(rand(100)+1) % 23 == 0) {
        print "Yada-Yada error, restarting loop\n";
        $i = 0;
        $restartcount++;
    }

    # Simulate a condition that requires an abort
    if(int(rand(1000)+1) == 42) {
        print "Fatal error, aborting after $restartcount tries\n";
        $done = 0;
        last;
    }
}

if($done) {
    print "Loop done\n";
    print "Had to restart $restartcount times\n";
}

[download]

There is only a very small chance that the Perl interpreter is even theoretically capable of predicting when it is the last loop... until it exits the loop in one of three completely different ways. Depending on how borked your pseudo-random number generator is, it's theoretically possible that the script will never exit the loop. It's a classic halting problem. Alan Turing himself stated that it's impossible to predict the outcome.

perl -e 'use Crypt::Digest::SHA256 qw[sha256_hex]; print substr(sha256_hex("the Answer To Life, The Universe And Everything"), 6, 2), "\n";'

In reply to Re: Perl's feature to determine, in current point of loop, that this is the last one? by cavac
in thread Perl's feature to determine, in current point of loop, that this is the last one? by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.