The file permissions that ls -l shows up does not have executable permissions for the user i.e you i.e davidlee. So you need to set the executable permissions for the script file (myscript). to do this give chmod u+x myscript
the ls -l myscript will then show
-rwx-r--r-x
i.e you now have the executable rights and now you can run myscript by typing just the filename.
Hope this works.