As article 6.2 explains, UNIX programs can never, ever modify the environment of their parents. A program can only modify the environment that later will be passed to its children. This is a common mistake that many new UNIX users make: they try to write a program that changes a directory (or does something else involving an environment variable) and try to figure out why it doesn't work. You can't do this. If you write a program that executes the cd command, that cd will be effective within your program - but when the program finishes, you'll be back in your original (parent) shell.
you could use the following commands to change the current directory of the current shell:
The source and
read a script file into the current shell instead of starting a child shell.
These commands only work for shell script files (files containing command
lines as you'd type them at a shell prompt).
You can't use
. to read a binary (directly executable) file into the shell.