The /proc filesystem does provide a cwd of the process which combined with a rel2abs() could provide the information desired but since it changes if the script changes - it too is unreliable.

I think is your only option, especially for scripts.

Scripts are really just arguments to proper binary executables. There is no kernel process structure to store the full path to arguments that happen to be file name values.

Also, I hate to bear bad news but, the shell guys can still drive you crazy if they don't put the she-bang at the top of their scripts. Take a look at this:

me@mybox:/home/me/sandbox
$ ./2.sh &
[1] 417964
me@mybox:/home/me/sandbox
$ ps -o pid,args -p 417964
   PID COMMAND
417964 -bash
me@mybox:/home/me/sandbox
$ ./1.sh &
[2] 430266
me@mybox:/home/me/sandbox
$ ps -o pid,args -p 430266
   PID COMMAND
430266 /usr/bin/bash ./1.sh
[download]

me@mybox:/home/me/sandbox
$ cat 1.sh
#!/usr/bin/bash
sleep 600
me@mybox:/home/me/sandbox
$ cat 2.sh
sleep 600
[download]

Yes, I use bash on AIX. Linux has spoiled me.