What is the purpose of the PATH variable?

Question

a. Set the PATH variable and place it in the environment so it causes the
shell to search the following directories in order:
• /usr/local/bin
• /usr/bin
• /bin
• /usr/kerberos/bin
• The bin directory in your home directory
• The working directory
b. If there is an executable file named doit in /usr/bin and another file with
the same name in your ~/bin directory, which one will be executed?
c. If your PATH variable is not set to search the working directory, how can
you execute a program located there?
d. Which command can you use to add the directory /usr/games to the end
of the list of directories in PATH?

Answer 1

When you give the shell a simple filename as a command, the shell searches
through directories specified by the PATH variable for the program you
want to execute. It looks for a file that has the same name as the command
and that you have execute permission for (a compiled program) or read and
execute permission for (a shell script).

a. The following command sets the PATH variable as specified and places
it in the environment:
$ export PATH=/usr/local/bin:/usr/bin:/bin:/usr/kerberos/bin:~/bin:.:
b. The /usr/bin/doit file will be executed because /usr/bin appears before
~/bin in PATH.
c. You can execute the command by giving either an absolute pathname or
a relative pathname such as ./program-name.
d. $ PATH=$PATH:/usr/games