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To use utilities, you must use the shell.
Specifically, you tell the shell to execute a utility on your
behalf.
The most basic tool provided by
the shell is the command interpreter. Specifically, the shell
executes utilities (or programs) specified by the user.
To execute a utility, you must follow the
basic format of command followed by a "-" followed by optional
options and arguments as in:
command -options arguments
Right off the bat, you may execute
any of the utilities found in "/bin" or "/usr/bin". You can
also use the command interpreter to execute any executable
utility that you install.
| Another cool way to run
commands is to use the backtick character (`). essentially, the
backtick surrounding a command means that the shell should execute it.
This is most commonly used when more than one command are interacting
as you will see later... |
We are going to talk more about all
the utilities you have at your disposal in the next couple
of days, but for now, lets just work with the "ls" utility
used to list the contents of a given
directory. This utility demonstrates how "all" commands are
executed in general.
As we said, a utility can be
run simply by typing its name at the command line
as in the following case where we simply type "ls"
at the command line: (Notice that the "ls" utility reports
that there are three files in this directory)
![[ls]](Images/ls.gif)
However, many utilities also take options
that modify how the command is executed. For example,
consider the -l option for the "ls" command. This
option produces a more detailed listing. We will talk more
about the meaning of the listing later. Just notice
how the option was applied to the comand generically.
| In order to stop a command while it is running, you
should press the BREAK or DELETE key. If that does not work, try hitting
CNTRL-D or CNTRL-C. |
![[ls-l]](Images/ls-l.gif)
Finally, many utilities also take
arguments. For example, to get a listing of all the files
with . extensions, you might use the following: (We will talk more about
the "*" argument later. For now, just notice the lack of the
Mail directory which appeared in the other listings)
![[ls arguments]](Images/ls_args.gif)
| You can execute several commands on the same comand line by
separating them with a semi-colon such as:
$ ls -l; who; cal; pwd.
Likewise, if you do not
want to wait for the command to finish before you continue working, you can request that
UNIX performs the command in the background. To do so, you use the "&" character
such as:
$(ls > dir.txt)&
Finally, you can keep a job alive even after you logout by
using the nohup (no hang up) utility such as:
nohup sort address_book > sorted_addresses &
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If you are not sure what arguments
or options a command takes you can always use the
generic -? or --help, which will give you some hints. the
following image shows a help request for the "pwd" command
![[Command Help]](Images/help.gif)
Of course, the "man" command,
that we will discuss later, or a good reference book
may be a better resource.
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