This is not completely correct, I think:

for /proj/home/me/asdf.p your code would correctly give: /proj/home/me/

but for asdf1.pl the result would be: asdf1.pl

another approach:

my $temp1 = "/proj/home/me/asdf.pl";
print my_dirname($temp1) ."\n";

$temp1 = "asdf1.pl";
print my_dirname($temp1) ."\n";

$temp1 = "/asdf1.pl";
print my_dirname($temp1) ."\n";

sub my_dirname {
  my ($dir) = $_[0] =~ m|^(.*/)|;
  return $dir;
}
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