#!/usr/bin/perl
use strict;
use warnings;

our $data;

print "\n\n original\n";
foreach (split("\n",$data))
{
    if(/start/ .. (!(/start/../end/) && /end/)) 
        { print "$_\n"}
}

print "\n\n analysis:\n";
print "    - note that range operator is set to true when \$flag1 is t
+rue\n";
print "           becomes false only after \$flag3 has been set to tru
+e\n";
print "\n";
foreach (split("\n",$data))
{
    my $flag1=0;my $flag2 = 0;my $flag3=0;
    $flag1 = 1 if (/start/);
    $flag2 = 1 if (/start/../end/);
    $flag3 = 1 if (!$flag2 && /end/);
    
    print "$flag1, $flag2, $flag3, $_",' 'x(15-length($_));
    
    if(/start/ .. (!(/start/../end/) && /end/)) 
        { print "success\n"}
    else {print "\n";}
}


BEGIN {
    our $data = << 'TEST';
a
a
a
start
b
    start
    c
    d
    e
    end
    f
    start
    g
    h
    i
    end
j
end
k
k
l
TEST
}
[download]

result

 original
start
b
    start
    c
    d
    e
    end
    f
    start
    g
    h
    i
    end
j
end


 analysis:
    - note that range operator is set to true when $flag1 is true
           becomes false only after $flag3 has been set to true

0, 0, 0, a
0, 0, 0, a
0, 0, 0, a
1, 1, 0, start          success
0, 1, 0, b              success
1, 1, 0,     start      success
0, 1, 0,     c          success
0, 1, 0,     d          success
0, 1, 0,     e          success
0, 1, 0,     end        success
0, 0, 0,     f          success
1, 1, 0,     start      success
0, 1, 0,     g          success
0, 1, 0,     h          success
0, 1, 0,     i          success
0, 1, 0,     end        success
0, 0, 0, j              success
0, 0, 1, end            success
0, 0, 0, k
0, 0, 0, k
0, 0, 0, l
[download]