smartperl:

When I see a problem like this, I normally break it apart into steps. Then, if I can't immediately write down the solution to any of those steps, I break the steps down even further. Something like:

my $spec="11-29,39-72,99-100,103,107";
my $input = "The quick red fox jumped over the lazy brown dog.";
# break spec into set of offsets and lengths

# for each offset and length...
for (my $idx=0 .. $#specs) {
   my ($input, $offset) = # how did I store them?

   #...extract a substring...
   my $substring = substr($input, $offset, $length);

   #...then print the result
   print "<$substring> is substr(...,$offset,$length)\n";
}
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Ok, I handled the easy part. Now I break down each comment that doesn't have code. Keep doing that until everything is done.

When you start out, you sometimes get a problem that seems complicated, but if you start breaking it down into subproblems, you often find that it's just a few trivial bits glued together.

...roboticus

When your only tool is a hammer, all problems look like your thumb.