Ummm, I'm not exactly sure what $basedir is supposed to mean. Perhaps something like this will show you a solution?

#!/usr/bin/perl -w
use strict; # always
use File::Basename;
my $prog    = $^X;
my $basedir = dirname($prog);

print "prog   : $prog\n";
print "basedir: $basedir\n";
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Which outputs:

prog   : /usr/bin/perl
basedir: /usr/bin
[download]

Cheers,
Shendal