Because reverse in list context reverses the order of the items in the list; in scalar context it reverses the characters in a string. Just like the documentation says it does.

Update: And your confusion may be from the fact that print is providing a list context to reverse which is triggering its reverse-a-LIST behavior even though it's only been given a single element list.

This is called being called "in scalar context" or "in list context".

This allows the same function to do two different useful jobs, but can be surprising to someone who expects the following snippets to do the same thing (which they might not):

# ------------------------------
# Call in array context
# wantarray() will return true inside some_function
my @ary = some_function;

# And see how many items were returned.
my $num_items = scalar @ary;

# ------------------------------
# Call with explicit scalar context:
# wantarray() will return false inside some_function
my $num_items = scalar some_function;

# $num_items might or might not be the same as the array
# context call above, depending on whether some_function
# chooses to check want_array and do something different.

# ------------------------------
# Call with explicit scalar context:
# wantarray() will return false inside some_function
my $num_items = some_function;
# As above.
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Reading the docs for reverse, one sees that it will reverse a string in scalar context (

results in $doog being set to 'doog'), but it will reverse the order of the elements of a list in list context (

results in @doog = ('good'), as a 1 element list looks the same when reversed (Perl may even optimize the reverse away in this case).

Since print expects a list (print ($a, $b, $c) is perfectly valid Perl), Perl's behavior for

print reverse('good');
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is the same as it is for

@doog = reverse('good');
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The solution is to convince reverse you want a scalar, not an array. There are many ways to do this:

# 1. Assign it to a scalar:
$a=reverse("monks");

# 2. Use the keyword "scalar":
print scalar reverse("monks");

# 3. Use some kind of scalar-based manipulation
print reverse("monks")."\n";

# 3a: do almost the same:
print reverse("monks")."";

# 3b: (reverses 100 to 001, then adds 1, printing "2".
print reverse(100)+1;
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