Environment Variables (35.3)
Setting Up Your Environment
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Environment Variables
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Aliases
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Setup Files
–
.login
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.tcshrc
–
other .*rc files
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History
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Command Completion
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Unlike a regular shell variable, an environment
variable is inherited by another shell or program
that you start.
A Unix process cannot change its parent's
environment.
Environment variables hold information that you
would normally have to commonly specify in shell
commands or for Unix utilities.
Environment information is passed to a C program.
int main(int argc, char *argv[], char *env[]);
Setting Environment Variables (35.3)
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General form. In the csh or tcsh, use the
following command to set an environment
variable. The general convention is to use capital
letters for environment variables and lowercase
letters for regular shell variables.
Unsetting Environment Variables
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setenv <name> <value>
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Examples:
setenv EDITOR vi
setenv DISPLAY lov301:0.0
Sometimes it is desirable to undefine an
enviroment variable. You can do this with the
unsetenv command.
General form.
unsetenv <name>
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Examples:
unsetenv EDITOR
unsetenv DISPLAY
Displaying the Value of an
Environment Variable
Predefined Environment Variables (35.5)
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The setenv command by itself will display the
values of all of your environment variables.
setenv
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You can also print out the variables using a
printenv command.
printenv [<environment variable name>]
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You can always display a specific environment
variable using:
echo $<environment variable name>
Predefined Environment Variables
(cont.)
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SHELL: Contains the absolute pathname of your
shell.
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USER: Contains your username.
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TERM: Contains the name of your terminal type.
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DISPLAY: Used by the X Window system to identify
the display server.
Predefined means that their name and use is
predefined. You still have to usually define them
yourself.
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PATH: Contains a list of directories separated by
colons in which the shell looks to find commands.
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EDITOR: Name of your favorite editor.
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PRINTER: Name of your default printer.
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PWD: Contains the absolute pathname of your current
directory. Set by the cd command.
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HOME: Contains the absolute pathname of your
home directory.
Aliases (29.2, 29.3)
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The alias facility allows you to define
abbreviations for commands.
General form.
alias <name> <string>
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Examples:
alias lprd “lpr -Z duplex”
alias ls “ls -F”
alias web “ssh websrv.cs.fsu.edu”
Which (2.6, 35.27)
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The which command can be used to print out the
value of an alias or the pathname of a utility.
which ls
which sort
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Related commands:
Removing Aliases
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unalias web
Source Command (35.29)
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General form.
set prompt = <string>
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Examples:
set prompt = “csh% ”
set prompt = “`hostname`% “
Examples:
unalias ls
Setting Your Command Prompt (4.1)
You can set your prompt at the command line.
General form.
unalias <name>
whatis – print a one line summary of the command
whereis – locate the binary, source, and man pages for a
command
alias – without the string definition, it prints the current
alias for a command
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The unalias command allows you to remove
aliases that were previously specified.
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It would be desirable to create a shell script that
defines your environment variables and aliases.
But invoking a shell script creates a child process
and thus the script cannot update the environment
variables or aliases of the parent process.
The source command (csh and tcsh) reads a script
file into the current shell instead of starting a
child shell. All definitions of variables and
aliases are retained.
source ~/.tcshrc
The .login File (3.3)
Shell Setup Files (3.3)
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Shell setup files are invoked automatically at the
start of specific events.
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Types:
The .login file is invoked in the csh or tcsh when
you login to a Unix system.
Tasks typically performed in a .login file include:
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Setting environment variables, which are passed to
subshells automatically.
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.login
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.tcshrc
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Setting the I/O options for your terminal.
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other .*rc files
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Performing commands you wish to run once each
time you login.
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The .tcshrc File
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The .tcshrc file is run any time a tcsh shell starts.
If the .tcshrc file does not exist, then the .cshrc
file is invoked. The tasks performed are often
those that set definitions that are not passed to
subshells.
Tasks typically performed in a .tcshrc file
include:
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setting aliases
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setting your command line prompt
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setting the history variable (will be discussed later)
Check news, mail, calendar, etc.
Other .*rc Files (3.20)
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A variety of different commands use a .*rc file in
your home directory to perform some type of
initialization. Some applications require that you
prepare the .*rc file, while others will set one up
automatically for you. The more complex
applications may have a setup subdirectory off of
your home directory.
Common .*rc Setup Files
The .mailrc Setup File
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.mailrc: used with mail and related mailers
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.gvimrc: used with the gvim editor
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Setup aliases for email addresses.
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.newsrc: used with news readers
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Setup the default editor for your mailer.
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.procmailrc: autonomous mail processor
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Specify a file that records outgoing messages.
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Specify a command to print a message.
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Specify a sound when you receive a message.
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.acrorc: used with the acroread pdf viewer
.xfigrc: used with the xfig picture editor
The .gvimrc Setup File
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.gvimrc: for use with the gvim editor (similar in
purpose to the .emacs file)
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Set the background of the window.
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Set the size and type of the font.
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Set the number of width and height in characters.
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Set whether syntax highlighting is turned on or off.
.mailrc: for use with mail and related mailers
The .newsrc Setup File
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.newsrc: for use with news readers
News readers allow you to read articles that are
posted to particular newsgroups. One command
to use is trn (threaded read news program).
The .newsrc file is automatically created by trn if
it does not find one.
The .newsrc file is automatically read by trn and
you are given the option to add new newsgroups
that have been recently created.
Other Common .*rc Setup Files
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History (30.1)
Other common .*rc setup files:
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.pinerc – setup file the pine mailer
.procmailrc – setup for the autonomous mail processor
that can be used to filter spam or generate automatic
replies
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.acrorc – setup file for the acroread pdf viewer to
indicate how to display a pdf file
Most shells contain a history of your most
recently entered commands.
You can retrieve these commands, make changes,
and reexecute them.
You can set the number of commands to save in
your history in your .tcshrc file.
set history=<number>
.xfigrc – contains recently accessed files by the xfig
picture editor
Extracting Portions of the Last
Command (30.3, 30.4, 30.8)
Command History Substitution
(30.5,30.7,30.8,30.9)
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There are many options for performing command
history substitution.
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You can also extract portions of the last command to
be used in the current command.
!!
repeat the last command
!$
take the last argument from the previous command
^pat^rep
repeat last command replacing pat with rep
!^
take argument 1 from the previous command
!-n
repeat the last nth previous command
!*
take the first through the last arguments
history
display the history list of commands by number
history num
display the last num commands
!num
repeat the command numbered num
!:n* take the arguments n through the last argument
from the previous command where the first
argument is numbered at 0
!pat
repeat last command that starts with pat
Extracting Portions of Last Command Exs
# using the last argument from the previous command
ps2pdf t.ps t.pdf
acroread !$
# using argument 1 from the previous command
cp t.c t.c.old
vi !^
# using all of the arguments from the previous command
gcc main.c input.c proc.c output.c
lpr !*
# using arguments n through the last argument
chmod +x ns.sh nd.sh ir.sh pd.sh pf.sh
lpr !:2*
Complete Word Function (28.6)
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In the tcsh you can complete a word by pressing
the TAB character if the characters typed so far
are unique.
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Complete the name of command that is in your path
when the word is the first word on the command line.
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Complete the name of a file that is in the current or
specified directory.
Shell Command-Line Editing (30.14)
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The tcsh allows you to use the arrow keys and
other special characters to retrieve previous
commands and to edit them.
Arrow key bindings:
up
go back one command
down
go forward one command
left
go backward one character
right
go forward one character