| Knowledge of file and directory
management using commands is very important in building a solid
foundation for further study of the UNIX operating system. Power UNIX
users and system administrators must have a working knowledge of
command line capabilities and syntax. Many operating system management
and device configuration tasks require an understanding of UNIX
commands, and in some cases, the command line is the only tool
available. Power users and administrators frequently create executable
script files, which are powerful tools for automating certain tasks
such as backing up files or creating new user accounts. Script files
are a series of UNIX commands and are similar to batch files used with
other network operating systems.
Control characters are used to perform
specific tasks such as stopping and starting screen output and others
as listed in Figure .
There are two control keys on most PC keyboards. They are normally
labeled Ctrl and found in the lower left and right corners of
the keyboard. On a Sun workstation, there is one control key in the
lower left of the keyboard which is labeled Control. When
displayed on the screen, the Control key is represented by the caret
(^) symbol.
To enter a control character sequence,
hold down the Control key and press the appropriate character on the
keyboard. Control-c is a common control character sequence and
is frequently used to interrupt or cancel a process. The actual character in the
shell appears as ^C, even though you press the Control key and
the c key at the same time. The following control characters can be
used:
- Control-s - Stops screen
output. The Control-s and Control-q characters were originally
needed by teletype operators and are rarely used today. An example
of when you might use the Control-s is when viewing a large file
with the
cat command
(covered later).
- Control-q - Resumes screen
output stopped by Control-s and is not used frequently.
- Control-c - Interrupts the
current activity and is frequently used to abort processes or long
display outputs resulting from the man,
cat or
ls commands. If you do a
man page on a command and want to stop the remaining display of
the man output, you can press Control-c to interrupt the output
and return to a command prompt.
Control-c is also helpful in restoring the shell prompt if
an unrecognized command line (i.e., $ls
" ) is typed and the
secondary prompt (>) in the Korn shell is received.
- Control-d - Indicates
end-of-file or exit. Control-d is used to exit some UNIX utilities
(bc, write, and several others), exit a terminal window, and to
log out of a terminal session or command line login session. As a general rule, when
stuck or
if Control-c does not work, try Control-d.
- Control-u - Erases the entire
command line. This can be used as a quick way to erase a command
line that you decided not to execute or in cases where you are
logged into a remote system and the backspace key does not work.
It can also be used to ensure that you are starting with a fresh
user id and password entry when logging in. Because passwords
cannot be seen when they are typed, use Control-u to erase the
password and start over when an incorrect character(s) has been
typed.
- Control-w
- Erases the last word on the command line. This can be used as a
quick way to erase the last argument (i.e., a pathname or file
name) on the command line that you decided not to use or in cases
where you are logged into a remote system and the backspace key
does not work.
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