use File::Basename;
my $baseLoc=($0=~/\//)?dirname($0):
  (grep { -x "$_/$0"} split ":", $ENV{"PATH"})[0];
[download]

That is, if there's a / in the executable, all well and good: it's been told precisely where it is. Otherwise, check through all the elements of the PATH environment variable, until we find an executable with this name.

Note that this will go horribly wrong if somebody invokes your script directly using perl, rather than letting the kernel decide on the interpreter, as a few seconds thought about what'll happen if the execution command was: perl ls

Update:dmerphq has just pointed out in the CB that $0 is always set to the full path and filename, if the user has relied on the normal path searching. So you can get away with just using dirname($0)

see Re: How do I get the full path to the script executing? for a longer explanation.

--
Tommy
Too stupid to live.
Too stubborn to die.