Challenge 3: Fix the Missing or die — Possible Solution
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Given:
    open(my $fh, '<', 'does_not_exist.txt');

What happens when this runs against a genuinely missing file:
open() fails silently — it returns a false value, but since nothing
checks that return value, the script simply continues running with
$fh left undefined (or otherwise unusable), producing no visible
error at all; any later attempt to read from $fh either fails
quietly too or triggers a separate, more confusing warning far away
from the actual root cause.

Corrected version:
    open(my $fh, '<', 'does_not_exist.txt')
        or die "Can't open does_not_exist.txt: $!";

WHY THIS WORKS AS AN ANSWER
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The one-sentence explanation reuses this chapter's own warn-box
almost exactly — "a script that fails to open a file... continues
running anyway, silently doing nothing useful with an unopened
filehandle," described there as "a genuinely common source of 'my
script ran with no errors but produced no output' confusion." This
challenge asks specifically to state that consequence rather than
just avoid it.

The fix reuses the exact or die "..."; idiom the chapter establishes
as standard practice, first introduced with Chapter 5's own
open(...) or die pattern and reused throughout every open() call in
this chapter's own examples. Adding it here means a missing file now
produces an immediate, specific, human-readable error — "Can't open
does_not_exist.txt: No such file or directory" (via the $! special
variable, also reused from Chapter 5) — right at the point of
failure, instead of the silent, hard-to-diagnose non-failure the
original version produced.