Agenda

1. Agenda • Korn Shell • Korn Shell Variables • Korn Shell Variable Attributes • Korn Shell Arithmetic • Functions

2. Korn Shell • The Korn shell was developped to incorporate Bourne shell as well as incorporate many features of the C shell • The Korn shell also has many features including improved math processing, aliases, variable attributes and history capabilities • The default shell for PHOBOS is the Korn shell.

3. Z & Bash Shells • The Z shell is Linux’s equivalent to the Korn shell - Z shell is available on TUX • The Bash shell has evolved to contain many of the features of both the Bourne shell and Korn shell

4. Running Shells • If your system allows you access to the shell, you can switch to a shell by issuing a command. • Eg. • Bash bash shell • zsh Z Shell • sh Bourne Shell • ksh Korn Shell

5. Setting a Default Shell • In some Linux and UNIX systems, you may be able to set your default shell upon logon by issuing the command: • chsh

6. Korn Shell Variables • The rules for Korn Shell variables are very similar as for Bourne Shell variables: • $1 - $9 are positional parameters (can use ${var} this allows for greater range • For user-created variables, variable name cannot begin with a digit and use assignment with an equal sign (no spaces on either side) • Variables can be removed using the unset command

7. Korn Shell Variables • Braces for variables can be handy to combine text together: • example: • SUFF=ization • echo org$SUFF • PREF=counter • echo ${PREF}clockwise Will display organization In order for text substitution to work in front of text, braces must be used. This example will display counterclockwise

8. Korn Shell Variable Attributes • One major way in which Bourne and Korn shells differ is that Korn shell can assign attributes to variables such as: • upper or lower case • integer • justification and width • The most useful attribute is integer since the variable does not have to be converted from text to an integer during processing

9. Korn Shell Variable Attributes • The typeset command is used to set an attribute for a variable • examples • typeset -u var (set var to be uppercase) • typeset -l var (set var to be lowercase) • typeset -i var (set var to hold an integer) • typeset -L3 var(set var as left justified with a width of 3) • typeset -R5 var(set var as right justified - width of 5)

10. Korn Shell Arithmetic • In the Korn shell, user-created variables can have an integer attribute. This makes it more efficient to perform math operations than the Bourne shell. • When performing calculations in the Korn shell using these variables, two expressions are used: • The let statement • The convention $((..))

11. Korn Shell Arithmetic • Example: • typeset -i x y • x=23 • y=37 • let result=x+y • echo $result • result=$((x+y)) • echo $result In first example, note how variables are set as integers. Also note with let command that no spaces are allowed In second example can use double-braces to perform math operations….

12. Z & Bash Shell Arithmetic • Syntax for Z shell arithmetic is the same as for Korn shell arithmetic • Bash Shell Arithmetic: • result=$[x+y] • echo $result • Note difference between Bash, Korn shell and Bourne shell syntax!

13. Command Substitution Syntax • The syntax rules for the Bourne, Korn (Z) and Bash shells are as follows: • Bourne Shell `command` • Korn (Z) Shell $(command) • Bash Shell $(command)

14. Functions • A function is a series of commands that are stored in computer’s main memory in order to allow quicker execution than executing a script. • Functions can also be contained within a shell script. As opposed to creating a function within the shell itself, a script containing a function will run slower since it is not stored in computer’s main memory

15. Functions After function entered (include brackets) type body of function at PS2 prompt - make sure to include braces. • Example: • who_is_here() • >{ • > date • > echo “Users Currently Logged On:” • > who -H | more • >} When end brace is entered, shell prompt will appear. To run function type who_is_here