Since it is ksh code, if you put:

Code:

#!/bin/ksh

At the very beginning of your script then it should run fine, provided that you make the script executable (chmod +x) and run it like /path/to/script, or like script if the path leading to the script is in your search path.

If you start the script like

Code:

bash script

then that will not work, since the first line is simply a comment and ksh will not be used.

You can also make sure ksh is used by calling it like:

Code:

ksh script

--
Actually it is the first two bytes and they inform the OS' program loader that the file is a script and that the remainder of the line specifies which command interpreter to run, with the script name as argument. This command interpreter is subsequently started and it then reads the script and typically interprets this first line - that starts with #! (the "shebang") - as comment, because it starts with #.