Because you created this function, I am assuming it is not sitting in /usr/bin/ or some such equivalent.  You have three options to get this to work: 

• modify your shell PATH variable to include the path to where this program resides
• use chdir from within your perl script to move to where the program resides
• specify the absolute path within the `` as so `/{fullpath goes here}/pscnt $inv_app_name $parameter`

Also, (I know this sounds basic) don't forget to check if the program has its execute bit set; I've seen sillier things overlooked...

Update:  I just noticed you created this shell script in your .profile; if possible don't do that.  .profile is normally for configuration settings and other such stuff.  Instead, put your shell script in a seperate file with (I think) #!/usr/bin/sh (or replace the sh with whatever shell happens to be the one you want the script to run under) as your first line; then set the execute bit on the new file.