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Setting up your environment Fall 2006
Setting up your environment
Setting up your environment
 Environment variables these variables are passed to
child processes
 Aliases modify the meaning of commands
 History a record of your shell commands
 Command completion lets you save keystrokes
COP 4342 Fall 2006
Setting up your environment
Environmental variables
 Environmental variables are passed to child processes
at invocation. (The child process can of course ignore
them if it likes.)
 Children
cannot
modify
parents
environmental
variables any modication by a child process are
local to the child and any children it might create.
COP 4342 Fall 2006
Setting up your environment
Environmental variables
 The traditional C main is usually dened something
like:
int main(int argc, char *argv[], char *envp[])
COP 4342 Fall 2006
Setting up your environment
Setting environmental variables
CSH/TCSH: setenv VARIABLE VALUE
BASH: export VARIABLE=VALUE
old SH: VARIABLE=VALUE ; export VARIABLE
Note: there are a few special variables such as path
and home that CSH/TCSH autosynchronizes between the
two values.
COP 4342 Fall 2006
Setting up your environment
Setting environmental variables
[langley@sophie 2006-Fall]$export VAR1=value
[langley@sophie 2006-Fall]$ bash
[langley@sophie 2006-Fall]$ echo $VAR1
value
[langley@sophie 2006-Fall]$ exit
exit
[langley@sophie 2006-Fall]$ csh
[langley@sophie 2006-Fall]$ echo $VAR1
value
COP 4342 Fall 2006
Setting up your environment
Setting environmental variables
[langley@sophie 2006-Fall]$ csh
[langley@sophie 2006-Fall]$ setenv VAR2 bigvalue
[langley@sophie 2006-Fall]$ csh
[langley@sophie 2006-Fall]$ echo $VAR2
bigvalue
[langley@sophie 2006-Fall]$ exit
[langley@sophie 2006-Fall]$ exit
[langley@sophie 2006-Fall]$ bash
[langley@sophie 2006-Fall]$ echo $VAR2
bigvalue
COP 4342 Fall 2006
Setting up your environment
Unsetting environmental variables
CSH/TCSH: unsetenv VAR
SH/BASH: unset VAR
You can also leave it as local variable in bask with
export -n VAR.
COP 4342 Fall 2006
Setting up your environment
Unsetting environmental variables
[langley@sophie 2006-Fall]$ csh
[langley@sophie 2006-Fall]$ setenv VAR99 testvar
[langley@sophie 2006-Fall]$ csh
[langley@sophie 2006-Fall]$ echo $VAR99
testvar
[langley@sophie 2006-Fall]$ unsetenv VAR99
[langley@sophie 2006-Fall]$ echo $VAR99
VAR99: Undefined variable.
[langley@sophie 2006-Fall]$ exit
[langley@sophie 2006-Fall]$ exit
[langley@sophie 2006-Fall]$ echo $VAR99
testvar
COP 4342 Fall 2006
Setting up your environment
Unsetting environmental variables
[langley@sophie 2006-Fall]$ export VAR50=test
[langley@sophie 2006-Fall]$ bash
[langley@sophie 2006-Fall]$ echo $VAR50
test
[langley@sophie 2006-Fall]$ unset VAR50
[langley@sophie 2006-Fall]$ echo $VAR50
[langley@sophie 2006-Fall]$ exit
exit
[langley@sophie 2006-Fall]$ echo $VAR50
test
[langley@sophie 2006-Fall]$ export -n VAR50
[langley@sophie 2006-Fall]$ echo $VAR50
test
[langley@sophie 2006-Fall]$ bash
COP 4342 Fall 2006
Setting up your environment
[langley@sophie 2006-Fall]$ echo $VAR50
COP 4342 Fall 2006
Setting up your environment
Displaying your environment
BASH: env, printenv, set, declare -x, typeset
-x
CSH: env, printenv, setenv
COP 4342 Fall 2006
Setting up your environment
Predened environmental variables
What is predened is not so much the value of the
variable as its name and its normal use.
 PATH : a list of directories to visit. They are delimited
with :.
Note that csh/tcsh autosynchronize this
variable.
 EDITOR : the default editor to start when you run a
program that involves editing a le, such as crontab
-e.
COP 4342 Fall 2006
Setting up your environment
 PRINTER : the default printer to send to.
 PWD : your present working directory.
 HOME : your home directory.
 SHELL : the path to your current shell. (Be cautious
with this one: in some shells, it is instead shell).
 USER : your username.
 TERM : your terminal type.
 DISPLAY : used by programs to nd the X server to
COP 4342 Fall 2006
Setting up your environment
display their windows.
COP 4342 Fall 2006
Setting up your environment
Aliases
An alias allows you to abbreviate a command. For
instance, instead of using /bin/ls -al, you might
abbreviate it to ll with:
SH/BASH: alias ll=/bin/ls -al
CSH/TCSH: alias ll /bin/ls -al
COP 4342 Fall 2006
Setting up your environment
Removing aliases
You can remove an alias with unalias.
Example:
unalias ll
COP 4342 Fall 2006
Setting up your environment
which, whatis, whereis, locate
The program (or built-in) which simply gives you the
path to the named executable as it would be interpreted
by your shell invoking that executable, and is created by
examining your path.
The program locate looks in a database for all
accessible les in the lesystem that contain the substring
you specify. You can also specify a regular expression,
such as
locate -r ab.*ls
COP 4342 Fall 2006
Setting up your environment
The program whatis will give you the description line
from the man page for the command you specify. (N.B.:
You can also search the man page descriptions with man
-k keyword.)
The program whereis will give you both the path to
the executable named and the page to its manpage.
COP 4342 Fall 2006
Setting up your environment
Setting your prompt
SH/BASH: PS1=%
CSH/TCSH: set prompt=%
COP 4342 Fall 2006
Setting up your environment
Sourcing commands
Because ordinarily running a shell script means rst
forking a child process and then exec-ing the script in that
child shell, it is not possible to modify the current shells
environmental variables from just running a script.
Instead, we do what is called sourcing the script,
which means simply executing its commands (such as
setting environmental variables) inside the current shell
process.
COP 4342 Fall 2006
Setting up your environment
CSH/TCSH: source FILE
SH/BASH: .
FILE
N.B.: modern versions of bash also support the source
built-in.
COP 4342 Fall 2006
Setting up your environment
.login , .profile
When you login, your user shell is started with -l. For
sh/bash, this means that shell will source your .profile
le; for csh/tcsh, this means sourcing your .login le.
Typically, you would want your environmental variables
in that le, and any other one-time commands that you
want to do when logging in, such as checking for new
email.
COP 4342 Fall 2006
Setting up your environment
Shell .*rc les
For each shell that you start, generally a series of run
command les, abbreviated as rc will be sourced. In
these you can set up aliases and variables that you want
for every shell (including those that are not interactive,
such as those running under a crontab.)
BASH: .bashrc
CSH: .cshrc
There is also a .tschrc for tcsh. History, sh did not
COP 4342 Fall 2006
Setting up your environment
look for conguration les except when invoked as a login
shell.
COP 4342 Fall 2006
Setting up your environment
.*rc les in general
In general, many program use .*rc les. Some will ask
you to setup the le; some will create it for you. Some
want a whole directory.
 .gvimrc
 .procmailrc
 .gtkrc
 .xfigrc
COP 4342 Fall 2006
Setting up your environment
 .acrorc
COP 4342 Fall 2006
Setting up your environment
.gvimrc
 Set the background
 Set the size and type of the font
 Set the size of the window in characters
 Turn on or o syntax highlighting
COP 4342 Fall 2006
Setting up your environment
.procmailrc
The syntax is quite obscure, but you can apply arbitrary
rules to your incoming email via your .procmailrc le.
COP 4342 Fall 2006
Setting up your environment
.procmailrc example
DOMAIN="<$1>"
RECIPIENT="<$2>"
WHATSIT="<$3>"
VERBOSE=on
LOGFILE=/tmp/procmail2.log
LOGABSTRACT=all
ROOTHOMEDIR=/home/vmail-users
ROOTINBOXDIR=/var/spool/vbox
:0
* RECIPIENT ?? ()\/[^<]*@
* MATCH ?? ()\/.*[^@]
{
USER=$MATCH
}
COP 4342 Fall 2006
Setting up your environment
:0 a
* DOMAIN ?? ()\/[^<].*[^>]
{
DOMAINNOBRACKET=$MATCH
}
:0 a
${ROOTINBOXDIR}/${DOMAINNOBRACKET}/${USER}
COP 4342 Fall 2006
Setting up your environment
Shell history
You can modify the number of lines kept in your history:
bash: HISTSIZE=SOMENUMBER
csh/tcsh: set history=SOMENUMBER
Your shell history lets you do many things:
search
commands that you ran in the past, re-execute commands,
modify them, or save them o (bash lets you do the latter
automatically in your .bash history le.)
COP 4342