unix is user friendly -- it's just picky about who it's friends are...'' --...
DESCRIPTION
''Unix is user friendly -- It's just picky about who it's friends are...'' -- Unknown, seen in .sigs around the world. Basics of the Unix/Linux Environment. Shells and Your Unix Environment. What is a shell?. - PowerPoint PPT PresentationTRANSCRIPT
''Unix is user friendly --It's just picky about who it's friends are...''-- Unknown, seen in .sigs around the world
Basics of the Unix/Linux
EnvironmentShells and Your Unix Environment
What is a shell?Traditional user interface with the unix
operating system…it interprets your typing
A scripting program that controls the syntax at the command line interface
Just as there are many flavors of unix and unix-like systems, there are many types of shells
Common Shells
BourneShell
Bourne Again Shell
TENEXC shell
C ShellKornShell
shBourne shellthe original Unix shellPro: Flexible and powerful scripting shellCon: Not interactive or particularly user friendly
cshC shelldesigned for the BSD Unix systemsyntax closely follows C programmingPro: easy for C programmers to learn and comes
with many interactive features such as file completion and aliases
Con: not as flexible or powerful a scripting language
kshKorn shellderived from the Bourne shell so has a shared
syntaxjob control taken from the C shell
bashBourne-Again shellCombines the “best” of sh, ksh, and cshDefault shell on Linux and Mac OSX operating
systemsPro: Flexible and powerful scripting language
with all the interactive features of csh plus command completion
This shell is great for complicated GMT scripts
tcshTENEX C shellDefault shell of the CERI unix environmentPro: User friendly on the command line & it is
what your CERI account environment is set up to use
Con: It is not as suitable for long and involved scripts
It is perfectly good for most daily geophysics work on the command line & most faculty here use it on a daily basis so there are many experts around
What is my shell?env $SHELL will echo your current login shell to
the screento switch your shell in a single terminal window,
simply type the name of the preferred shellthe command line also usually indicates which
shell family you are using$ -- bash, sh, or ksh> or % -- csh, tcsh
Useful features of tcsh & bash
file completion: you can key the tab button to complete the name of a long file
history: list the previous commands entered during the active session
% history1139 11:19 ls | more | tail -n5 >> directory.list
up and down arrow keys: allow you to move up and down through previous commands
right and left arrow keys: allow you to edit command lines without starting from scratch
!XXX: reruns the command labeled XXX in the history list% !1139ls | more | tail -n5 >> directory.list
The Unix EnvironmentMitch has set up the basic CERI environment so
that everyone can access the standard geophysics packages available on the Sun system
But what does this mean?your environment is composed of a number of
environment variables which provide important information to the operating system
since you generally want the computer to behave the same way everyday, these environment variables are setup in configuration files accessed at login
What are your environment variables?
env: prints the current environment variables to the screen
HOME & SHELLHOME: this environment variable controls what
other unix commands consider your base or home directory
this is how “%cd “ knows which directory to go to% echo $HOME/gaia/home/hdeshon
SHELL: this variable stores your default shell% echo $SHELL/usr/bin/tcsh
*these environment variables should not be changed by the user
PATHPATH: tells the shell where to find applications and/or
executable files%echo $PATH
/gaia/smeagol/local/passcal.2006/bin:/gaia/smeagol/local/gmt/GMT4.2.1/bin:/opt/local/bin:/opt/local/sbin:/opt/csw/bin:/opt/csw/sbin:/ceri/local/bin:/usr/sbin:/ceri/local/sbin:/gaia/home/stbisrat/bin:/usr/local/bin:/opt/Studio/SUNWspro/bin:/opt/Studio/SUNWspro/prod/bin:/opt/sfw/bin:/usr/bin:/usr/dt/bin:/usr/openwin/bin:/bin:/usr/ucb:/usr/ccs/bin:/usr/local/teTeX/bin/sparc-sun-solaris2.8:/gaia/smeagol/local/bin
The : is used to separate each full path nameWhen a command is called from the command line,
the shell will search through this list of paths, in order, until it finds the first instance
How does PATH work?If you are working a program to do least squares
analysis and decide to call it “ls,” what will happen when you enter the command “ls”?
It depends on your PATH variable.When the shell goes looking through your path for
an executable file named “ls”, it will run the first one it finds.
If the directory containing your least squares program (executable file), “ls”, is in your path
Before
the directory containing the Unix list command, “ls”, it will run your program and you will not be
able (at least simply) to get a listing of your directory!
If the directory containing your least squares program, “ls”, is in your path
AFTER
the directory containing the Unix list command, “ls”, it will run the Unix ls command and you will
not be able (at least simply) to run your program!
To force your least squares executable in the current (working) directory to run
%./ls
To force the unix ls command to run
%/bin/ls
MANPATHMANPATH: tells the shell where to find the manual
pages read using the man command
%echo $MANPATH
/gaia/smeagol/local/passcal.2006/man:/gaia:smeagol/local/gmt/GMT4.2.1/man:/opt/local/man:/ceri/local/man:/usr/dt/man:/usr/man:/usr/openwin/share/man:/usr/local/man:/opt/SUNWspro/man:/opt/sfw/man:/usr/local/teTeX/man:/gaia/smeagol/local/man:/opt/csw/man
If you do a man on a command and the shell can’t find a manual page (and you are sure the man page exists), this environment variable may not be set correctly
HOST & REMOTEHOSTHOST: the name of the machine you are
currently logged intoREMOTEHOST: the name of the machine you
are sitting in front of, if different
% echo $HOST $REMOTEHOSTenigma sailfish2.ceri.memphis.edu
SSH Related VariablesSSH_CLIENT: the IP (internet protocol) address of
the HOST machineSSH_CONNECTION: the IP address of the HOST
machine and the REMOTEHOST machine
% echo $SSH_CLIENT $SSH_CONNECTION141.225.156.223 52372 22 141.225.156.223 52372 141.225.157.75 22
Modifying your current shell environment
If you mess up modifying the environment in your current window – you may “break” your current window (shell).
This is generally not a problem on the sun, mac, etc.
The environment is local to that window/shell.
Just close it and open another window.
set
set: sets csh shell variablesA typical tcsh set command is
%set history=100 This would save the last 100 commands on the history
list.
The bash equivalent is simply%history=100
setenvsetenv: the csh command to change
environment settings.
% setenv PATH {$PATH}:/gaia/home/hdeshon/scripts this adds the directory ‘~/scripts’ to the end of the
environment variable PATH within the active window
The bash equivalent is simply%PATH=$PATH:/gaia/home/hdeshon/scripts
setenv can be run on the command line, from within a local configuration file (.cshrc or .login), or in a shell script.
When run without specifying an environment variable, it will print all environment variables to the screen
Making your own environment variables
• Anytime you want a global definition of something, you can create your own global environment variable
%setenv LATESTRTVEL rtvel4_9305_5bv19
Modifying your default environment
It will get old changing everything to the way you want it each time you log in/open a new window/start a new shell. And this being Unix, there is a (easy) way to set up your own personal environment.
The setup of your personal environment (personal changes/preferences for how you want the shell to work for you) is stored in shell configuration files, aka dot files
.cshrc or .bashrc
There is also a file .login, but it is not likely you will have to change it (it get’s used when you log in, not each time you start a shell)
setenv PATH ${PATH}:/gaia/home/hdeshon/scripts
setenv LD_LIBRARY_PATH ${LD_LIBRARY_PATH}:/gaia/home/hdeshon/fftw-2.1.5/lib
setenv PRINTER 3876_grad
set filec #explicitly turns on file completion
set noclobber #turns on no clobber, which keeps redirect > from #overwriting files unless the ! is specified
set history=500 #keep the last 500 commands in the history list
alias l 'ls -F'
.cshrc
PATH=/usr/local/sod-2.2.2/bin:$ANTELOPE/bin:$PATH
export PATH
.bashrc
some warningsIf you need to modify your environment
configuration file (.cshrc, .bashrc), do so with care
Always leave two terminal windows open (prior to making any changes) in case you mess your file up so completely and break your active window, you have another window open to delete the offending file
Always backup the file you before modifying it!
Aliasesalias: creates a pseudonym or nickname for a
common command or series of commandsAnything you find yourself typing repeatedly can
be set to an aliasAnything you find yourself frequently mis-typing
can be set to an alias
unalias: unset the aliasalias and unalias can be run within a terminal
window for short-term usage or set in your configuration files for long-term usage
Aliases examplesalias settitlebar 'echo -n "^[]2;$CWD^G"'
alias cwdcmd 'set PROMPT="[${USER}@`hostname`] $CWD% "'
alias cd 'chdir \!* && cwdcmd && settitlebar’
alias howmuch 'du -sk .’
alias h 'history’
alias m more
alias mroe more
alias l 'ls -F'
alias c clear
alias src source
Sourcesource: executes configuration filesIf you change your configuration file, you will need to
execute the changes in all open terminal windows for the changes to take effect. They automatically will take effect when new terminal windows are opened.
%nedit ~/.cshrc you’ve used NEdit to make file changes
%source ~/.cshrc