The Korn Shell (ksh)

CS465 – Unix

ksh Shell

• The Korn (ksh) shell– Scripting syntax is compatible with the

standard Bourne (sh) shell

– Included in Unix operating systems from most vendors (Sun Solaris, SGI IRIX, Linux, etc.)

– Provides some extra features:• Command aliasing

• Easier user input and math calculations

• Command history

• Command-line editing

Command Aliases

Aliases allow you to define your own commands• Format:

$ alias [-x] name=definition

• Examples:$ alias ll="ls -la"

$ alias dir="ls -F"

$ alias –x home="cd;ls"

$ alias –x rm="rm -i"

Using the –x option “exports” the alias.

Command Aliases

• To remove aliases:$ unalias name

• To show all aliases:$ alias

• If you put the alias commands in your .profile or .kshrc file, you can use them every time you login.

Displaying Alias Values

• To determine which command a specific alias will run, use either alias OR whence:

$ alias ll="ls -la"

$ alias ll

ll='ls –la'

$ whence ll

ls –la

$

The Dash (-) Character• Dash (-) represents the previous working directory. When used to

cd, it automatically displays the current directory path.

• Example: Switching between one of your subdirectories and the system bin directory:

$ pwd/home/user1/sub1$ cd /bin$ pwd/bin$ cd -/home/user1/sub1$ cd -/bin$

The let command

• let provides built-in integer handling that easier to use and 10-30 times faster than expr

• Syntax:$ let math-expression

NOTE: Use = to assign values

• Examples

$ let i=i+1

$ let "prod = 12 * 6" Double quotes allow spaces and no backslash on *

The let commandCan use (( instead of let )):

x=3y=4((z = x * y)) Result: z = 12

((z = z + 1)) Result: z = 13

Notes: - No dollar sign ($) needed to access variable values

- Double parentheses act as quotes, so you can add spaces and don’t need to backslash metacharacters

let Operators– Integer operators:

+, -, *, /, %

– Integer comparisons: <, <=, ==, !=, >=, >

– Compounds

&& (and), || (or), ! (not)

NOTE: No backslashes needed inside (( ))

Bourne vs Korn Comparison

• Korn Shell

• Bourne Shell

[ $num -ge 0 ]

(( num >= 0 ))

[ $num1 -gt 0 -a $num2 -lt 100 ]

(( num1 > 0 && num2 < 100 ))

result=`expr calculation`

(( result = calculation ))

let example

i=1

total=0while (( i <= 100 ))do

(( total = total + i ))(( i = i + 1 ))

doneecho $total

Korn Additional test Operators

• The Korn shell also extends the test expression from the Bourne shell.

• By using two sets of square brackets, instead of one set, the system uses the Korn shell (instead of Bourne) to test specific conditions.

[[ test-condition ]]

Korn Additional test Operators

File Operators:-a file file exists

-L file file exists and is a symbolic link

f1 -ef f2 file1 and file2 are linked

f1 –nt f2 file1 is newer than file2

f1 –ot f2 file1 is older than file2

Logical operators:

&& logical AND

|| logical OR

Korn test example

$ cat lsdir

#! /bin/ksh

# lists directory contents if yours

if [[ -d $1 && -O $1 ]]

then

ls -l $1

else

echo Error - not a directory or not yours!

fi

exit

$

Command History• The Korn shells supports a history feature

that lets you recall previous commands, performing a substitution if necessary.

• The history command displays the previous 16 commands:

$ history

• Common Alias:

$ alias h="history"

r (recall/rerun command)

r alone repeats the last command.

r 11 repeats command number 11

r -2 repeats the command before the last one.

r d repeats the last command that started with a “d”.

r sort one=two repeats previous sort command using two instead one.

History Variables

• HISTFILE contains name of your history file

HISTFILE=$HOME/.myhist• If you do not provide a name, then the Shell uses:

$HOME/.sh_history

• HISTSIZE contains how many commands to save– Default (to save) is 128 (but show only last 16)

HISTSIZE=50

In-Line Command Editing

• You can perform vi in-line editing of the command line

• In-line edit mode enables you to edit a previous command on the current command line

• Use vi commands to move and edit the previous command line

Turning On/Off Editing

$ set [-+]o vi

set -o vi turns command-line editing on

set +o vi turns it off

Once turned on, ESC key activates the in-line editor

To use:

Press the ESC key to activate in-line editing.

Press – (or k) until the desired command appears.

Edit using vi commands, then press ENTER.

Using Command Line Editing

• Your command line now becomes a single line editor window into the command history file.

• The single line you start viewing is the current Shell command line.

• You can move to other lines by using the editor move commands (- moves backwards, + moves forwards).

• Editor search commands can also be used to select the line being viewed.

<ESC> Enter command mode

i/a Enter insert mode and add text before/after cursor

l Move cursor right

h Move cursor left

fc Move to character c

x Delete character

dw Delete one word

$ Move to end of line

<Enter> Execute the command

Some vi for Command Line Editing

Using Filename Completion

• Automated completion of a filename used as an argument to a command.

• To initiate, use the <ESC> key and a backslash

• Example:$ lsfile1 file2 fileofstuffnotes subdir whynot$ vi n<ESC>\

Uses vi to edit the file notes

Note: Only works when file completion is unique

• If the filename is NOT unique, you can get a list of choices by using: <ESC>=

• Example:$ cat f<ESC>=1) file12) file23) fileofstuff$ cat f_

Now when you press a number (1-3), that file is chosen and used to complete the command.

Filename Completion Choices

Additional Korn Shell Variables

$PPID the shell's parent process' PID

$_ last parameter of previous command

$RANDOM randomly generated integer (0-Max)

$ENV pathname of Korn shell environment startup file

$OLDPWD working directory set before current one

$EDITOR pathname of editor to use for line editing

$PS3 prompt for select loops (default is #?)

$TMOUT number of seconds to wait before exiting shell if no command is given

OLDPWD example

$ pwd

/home/smith123/cprogs

$ cd /etc

$ pwd

/etc

$ cd $OLDPWD

$ pwd

/home/smith123/cprogs

New Pattern Matching

~ home directory(equivalent to $HOME)

~username username’s home

~+ current working directory(equivalent to $PWD)

~- previous working directory(equivalent to

$OLDPWD)

Using Tilde Substitution$ pwd

/home/smith123/progs/cprogs

$ cd

$ pwd

/home/smith123

$ cd ~-

$ pwd

/home/smith123/progs/cprogs

$ cd ~jones456

$ pwd

/home/jones456

Reading User Input

• Korn shell provides one command that will BOTH “echo” and “read”:

• Syntax:

$ read 'varname?prompt'

• Examples:

$ read 'name?Enter your name: '

$ read 'year?Current year? '

read Example

$ mulEnter a number: 5Enter another number: 85 times 8 is 40$

$ cat mulread 'num1?Enter a number: 'read 'num2?Enter another number: '(( prod = num1 * num2 ))echo $num1 times $num2 is $prod$

until statement

until [ condition ]do

command(s)

done

• Same condition syntax as if statement

• Begin and end of command block defined by keywords do…done

• Loops UNTIL condition is TRUE

until Example

Read in a number from a user, and verify the number is positive.

$ cat posnum#! /bin/sh# Read positive number from usernum=0until [ num -gt 0 ]doecho Enter a positive non-zero number:read num

doneecho You entered $numexit 0$

until Example

Read in a number from a user, and verify the number is positive.

$ cat posnum#! /bin/sh# Read positive number from usernum=0until (( num > 0 ))doecho Enter a positive non-zero number:read num

doneecho You entered $numexit 0$

until Example Execution

$ posnumEnter a positive non-zero number:-50Enter a positive non-zero number:0Enter a positive non-zero number:12You entered 12$

select statement

select var in listdo

command(s)

done

• Implements a menu from within a loop. Automatically displays a numbered list of choices, and interpret the number that the user enters.

• Begin and end of command block defined by keywords do…done

select statement

• You must still use the case control structure to evaluate the choice chosen, but the structure will loop automatically unless you have chosen to exit.

• If your menu options consist of multiple words, they must be enclosed in double quotes.

select example$ cat junkit#!/bin/ksh# Menu-driven junkit scriptjunk=$HOME/junkdir## If junkdir directory doesn't exist, create itif [[ ! (-d $junk) ]]then 'mkdir' $junk

fi#select choice in "List junk" "Delete junk" "Junk files" "Exit"

do case $choice in "List junk")

ls -lgF $junk;;

select example

"Delete junk") rm $junk/*;;

"Junk files") read 'filelist?Enter files to junk: ' mv $filelist $junk;;

"Exit") break;;

*) echo Invalid choice; please try again;; esacdoneexit 0$

NOTE: The break command is used to exit the loop.

select execution

#? 3Enter files to junk: p2.c#?

$ pwd/export/home/jmsmith$ junkdir1) List junk2) Delete junk3) Junk files4) Exit#? 1total 0#?

#? 1total 2-rw------- 1 jwsmith 122 May 7 13:19 p2.c#? #? 2#? 1total 0#? 4$

Other Korn Additions:String Length

• Length of string: ${#varname}– Returns length of string stored in variable

• Example:$ cat namelenname="Pam Smallwood"echo ${#name}$ namelen13$

Other Korn Additions

• Forcing Command Execution– In addition to the back quotes (graves)`command`

– In Korn you can use: $(command)

• Example:$ name=$(whoami)

$ echo $name

small000

$

Sample .kshrc file

# Set command aliasesalias rm='rm -i 'alias rename='mv 'alias c clear# Set environment variablesPATH=$PATH:.PS1="$PWD[!] $ " EDITOR=vi# Export global variablesexport PATH EDITOR PS1# Set history variablesHISTSIZE=40

Default .profile

• Review handout

Capturing a Terminal Session

• You can capture what your terminal display to a file using the command script

• Syntax: $ script filename

• Everything that appears on your screen will be captured in the file, until you enter <ctrl-d>

Terminal Session Example

$ script session1Script started, file is session1$

$ cat session1$ pwd/export/home/small000$ dateThu May 22 19:34:25 MDT 2003script done on Thu May 22 19:34:29 2003$

pwd/export/home/small000$ dateThu May 22 19:34:25 MDT 2003$ <CTRL-d>Script done, file is session1$