Working with the Unix OS

Introduction to Unix
PS1=$
shell prompt
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
UBUNTU,SOLARIS: $prompt
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PS2=>
MAIL=/var/mail//grad0777
SHELL=/usr/local/bin/tcsh
TERM=xterm
HOST=kronos
quoted string prompt
mail box
shell program
terminal type
computer host name
Use the command "set" with no arguments to display the values of all shell environment variables.
All environment variables are strings. To change value or create a new variable, use a shell command of the form:
=
Example:
EXINIT="set redraw aw ai wm=0 number"
PS1="Please give me a command? "
Note that there is no space beside the equals sign.
If the string does not contain any characters that need quoting, then the quotes are not needed. i.e. no white space,
or pattern characters
Example:
TERM=vtl00 set terminal type
TMP=/tmp/junk
TMP="
set to null string
TMP=
Each process has its own copy of these environment variables. When a command is executed and a new process is
created by the shell, only the variables marked to be exported are copied into the new process.
Example:
export EXINIT TERM
Most variables set up by the system are already marked as exported. These exported variables are accessible within
C programs by using the library function getenv().
Example:
char *termtype;
termtype = getenv("TERM");
Note however that another program cannot modify the environment variables within the original shell. This is
because they exist in a separate process and only copies of these variables are available within the program.
Shell variables can also be used within the shell. Any shell command may contain variable names preceded by
dollar "$" to substitute it's value.
Example:
echo $HOME displays home directory
If a shell variable contains special characters such as white space or pattern characters then these are interpreted
after the variable is substituted.
Example:
LIB="curses"
CCFILES="yesno.o *.c"
CC=cc -o myprog -l$LIB $CCFILES
$CC assl kit
Is this the same as?
cc -o myprog -lcurses yesno.o assl.c kit.c
Command
Output
echo $CCFILES yesno.o ass1.c kit.c
echo "$CCFILES" yesno.o *.c
echo '$CCFILES' $CCFILES
Vi modes
7