First,

shorten this:

map { s/^-// } @ARGV;
  print join ("\n", @ARGV) . "\n";
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to this

print join "\n", map { s/^-// } @ARGV;
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now for an answer

In the first case, you were modifying $_ and as a result modifying@ARGV in place. Since you printed @ARGV, you got what you expected.

however, the second time, you received a number indicating the number of succesful matches. Check out the /gmodifier you want - to match more than once in the string.

Here is a simpler example that shows what was happening each time you applied your regexp to $_

$_ = 'aaaaaaaaaaa';

my $x = s/a//;

print "$x\n";
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