Shell reserved word??”Words reserved by the shell for special use. Many of these are
words that you would use in programming-type functions, such as do, while, case, and
else.
3. Function??”A set of commands that are executed together within the current shell.
4. Built-in command??”A command built into the shell. As a result, there is no representation
of the command in the file system. Some of the most common commands you will
use are shell built-in commands, such as cd (to change directories), echo (to echo text to
the screen), exit (to exit from a shell), fg (to bring a command running in the background
to the foreground), history (to see a list of commands that were previously
run), pwd (to list the present working directory), set (to set shell options), and type (to
show the location of a command).
5. File system command??”A command that is stored in and executed from the computer??™s
file system. (These are the commands that are indicated by the value of the
PATH variable.)
To find out where a particular command is taken from, you can use the type command. (If you
are using a shell other than bash, use the which command instead.) For example, to find out
where the bash shell command is located, type the following:
$ type bash
bash is /bin/bash
Try these few words with the type command to see other locations of commands: which, case,
and return.
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