Another potentially confusing variation would be if list context was used since the match will return the list of matched sub-expressions. In the example below, $input is assigned a value for each iteration wheras $1 is only changed on a good match.

#! /usr/bin/perl
use strict;

my $input;
while (<DATA>)
{
    ($input) = /(\w+)/;
    print "\$input=$input\t\$1=$1\n";
}
__DATA__
Hello

World
[download]

Output:

$input=Hello    $1=Hello
$input= $1=Hello
$input=World    $1=World
[download]