Linux.com: The Unix Shell, Part One

“The word Unix has traditionally brought to mind images of a
mystical operating system for high-end workstations and servers
that can only be gotten to through a cryptic command line interface
know as the Unix Shell. Linux with the help of graphical front
ends like GNOME has allowed people the power of Unix without
requiring them to learn a complex command line system. However, The
Unix Shell still has a lot to offer.
From the command prompt
simple programs or scripts can be quickly constructed to automate
repetitive tasks. Constructing larger and more complex programs can
also be done with minimal effort. The Unix Shell is a powerful tool
that can make life easier for anyone who is willing to invest a bit
of time learning the basic syntax.”

“Running programs from the Unix command line is easy, under
normal circumstances it is a matter of typing in the name of the
program you wish to run. For exanple, if you want to start the Pine
email client, just type “pine” at a command prompt. Pine will then
take control of the screen until you exit. Only programs located
within directories that appear in your PATH can be run in this
fashion. All of the directories that normally contain executable
programs should be in the default PATH. If you want to run a
program that is not in a directory that your path searches you must
specify the full path plus program name on the command line. For
example if you wanted to run the program hello, located in the /tmp
directory you would have to type in “/tmp/hello” the command will
work from any directory.”