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Using Linux Overview
[Shell Selection] [Shell Features]
[Environment Vars] [Jobs] [Files]
[Essentials]
Selecting a Shell
To some extent, the "feel" of interacting with a Unix system depends on
the command interpreter or "shell" that you are using. Different Unix systems
have different shells, and users can often select among a number of different
shells to suit their own tastes.
The most commonly used shell in the Linux world is "bash". It
is an enhanced version of a traditional shell known as the Bourne shell.
Bash is the "Bourne-again shell". Some other common shells are based
on the original "C" shell (csh).
Shell Features (tcsh and bash)
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Command recall.
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You can cycle through previous commands using the up and down arrows.
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Command/filename completion.
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If you type the first few characters of a command or file/directory name
and then press the tab key, the shell will attempt to complete the command
or name. If there is more than one valid completion, the shell will complete
the command up to the ambiguity. Pressing tab again will show the possible
completions.
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Filename wildcards.
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You can specify a "set" of files using "*" to represent a sequence of characters.
For example, "foo*" matches all the files starting with "foo".
Environment Variables
Environment variables are are often used in Unix to set general properties
of the system. For example the variable PATH determines what directories
will be searched when trying to lookup a command. DISPLAY determines the
machine on which windows will be displayed when using X, the Unix graphical
interface. Some useful commands:
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echo $<variable>
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Display the contents of the variable. Example: "echo $PATH"
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setenv <variable> <value> (c-shells only)
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Set the value of a variable. To add a new directory to a path, a c-shell
user would do something like "setenv PATH ${PATH}:/home/myfiles/bin". The
${PATH} is the old value of PATH and causes the new directory to be appended.
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unsetenv <variable> (c-shells only)
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Clears out an environment variable. For example, for a text-based login
session, a user might to "unsetenv DISPLAY" so that certain commands (e.g.
emacs) do not try to create a window.
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<variable>=<value>;export<variable> (Bourne-shells)
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Sets the value of an environment variable. Note there should be no spaces
around the "=". Example: "PATH=${PATH}:/home/myfiles/bin ; export PATH"
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<variable>=
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To unset a variable. Example "DISPLAY="
Sometimes there are some variables that we always want to set. We can customize
the environment automatically by placing shell commands in a file that
is automatically consulted when the shell starts. For bash, the commands
in ".bash_profile" are performed on login, and those in ".bashrc" are performed
whenever a new shell is started.. For c-shells, the commands in ".login"
are performed when you login, and those in ".chrc" are performed each time
you start a shell. Usually, you would modify the commands in .login. Note
these configuration files start with ".", so they are hidden files (see
section on files).
Job Control
To execute a command, simply type the name of the command at the shell
prompt. For example, to start the emacs text editor, type:
emacs <enter>. When the command has finished
executing, you will get back the shell prompt. Putting an "&" at the
end of a command causes it to run in the background. That is, the shell
prompt returns immediately so that more commands can be issued. The background
command will run concurrently with any subsequent commands. In this fashion, it
is possible to be running multiple "jobs" at the same time. Here are some
commands for manipulating multiple jobs:
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jobs
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List the currently running jobs.
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<ctrl>-z
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Suspend the current foreground job.
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bg
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Restart a suspended job in the background.
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fg
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Restart a suspended job in the foreground.
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kill %<number>
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kill (terminate) the job with the given number (obtained from "jobs").
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kill -9 %<number>
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Terminate with extreme prejudice.
Files and Directories
Unix maintains a tree-structured directory system. When you log in, you
are automatically placed in your "home" directory. You can make subdirectories
to organize your files. In referring to directories, there are some special conventions:
- '~' represents your home directory (can also use '$HOME')
- '.' represents the current directory.
- '..' represents the parent of the current directory.
Some file-handling commands:
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ls
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List files in directory.
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ls -l
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Directory listing in extended format.
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ls -a
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Directory Listing including hidden files (starting with ".").
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mkdir filename
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Create a new (sub)directory.
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cd directory
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Change directory.
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cd ..
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Change to parent directory.
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more filename
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display contents of file one page at a time.
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cat filename
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display contents of entire file.
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rm filename
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Delete the specified file.
Other Essential Commands
exit
Leave current command shell. At top-level, this logs you out.
yppasswd
Change your password on central password server.
man command
Display manual page entry describing the command.
man -k term
Display commands related to this term.
xterm (or konsole) &
Start up a graphical terminal (only used under X-windows).
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