If you run a {bourne, shell, etc.} script with a filename longer than 15 
characters, pidof -x will not find the running script.

To test, create a file called sleep.pl containing the following:

  #!/usr/bin/perl
  sleep 60;

Then create two links to this file:

  ln -s sleep.pl 15xxxxxxxxxxxxx
  ln -s sleep.pl 16xxxxxxxxxxxxxx

Start the first script and look for its pid:

  ./15xxxxxxxxxxxxx &
  pidof -x 15xxxxxxxxxxxxx

pidof will return the correct pid of the running script. Then do the same 
with the second script:

  ./16xxxxxxxxxxxxxx &
  pidof -x 16xxxxxxxxxxxxxx

Now pidof returns nothing. This does not seem to be affected by the script 
interpreter, length of total path, or any other factors.