CS465 – Unix
The Korn Shell
(ksh)
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
alias
alias
alias
ll="ls -la"
dir="ls -F"
–x home="cd;ls"
–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 command
Can use (( instead of let )):
x=3
y=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
• Bourne Shell
result=`expr calculation`
[ $num -ge 0 ]
[ $num1 -gt 0
-a
$num2 -lt 100 ]
• Korn Shell
(( result = calculation ))
(( num >= 0 ))
(( num1 > 0
&&
num2 < 100 ))
let example
i=1
total=0
while (( i <= 100 ))
do
(( total = total + i ))
(( i = i + 1 ))
done
echo $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
-L
f1
f1
f1
file
file
-ef f2
–nt f2
–ot f2
file exists
file exists and is a symbolic link
file1 and file2 are linked
file1 is newer than file2
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
r 11
r -2
alone repeats the last command.
repeats command number 11
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.
Some vi for Command Line Editing
<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
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:
$ ls
file1
file2
notes
subdir
$ vi n<ESC>\
fileofstuff
whynot
Uses vi to edit the file notes
Note: Only works when file completion is unique
Filename Completion Choices
• If the filename is NOT unique, you can get a list of
choices by using:
<ESC>=
• Example:
$ cat f<ESC>=
1) file1
2) file2
3) fileofstuff
$ cat f_
Now when you press a number (1-3), that file is chosen
and used to complete the command.
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
$ cat mul
read 'num1?Enter a number: '
read 'num2?Enter another number: '
(( prod = num1 * num2 ))
echo $num1 times $num2 is $prod
$ mul
Enter a number: 5
Enter another number: 8
5 times 8 is 40
$
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 user
num=0
until [ num -gt 0 ]
do
echo Enter a positive non-zero number:
read num
done
echo You entered $num
exit 0
$
until Example
Read in a number from a user, and verify the number is
positive.
$ cat posnum
#! /bin/sh
# Read positive number from user
num=0
until (( num > 0 ))
do
echo Enter a positive non-zero number:
read num
done
echo You entered $num
exit 0
$
until Example Execution
$ posnum
Enter a positive non-zero number:
-50
Enter a positive non-zero number:
0
Enter a positive non-zero number:
12
You entered 12
$
select statement
select var in list
do
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 script
junk=$HOME/junkdir
#
# If junkdir directory doesn't exist, create it
if [[ ! (-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;;
esac
done
exit 0
$
NOTE: The break command is used to exit the loop.
select execution
$ pwd
/export/home/jmsmith
$ junkdir
1) List junk
2) Delete junk
3) Junk files
4) Exit
#? 1
total 0
#? 3
Enter files to junk: p2.c
#? 1
total 2
-rw------1 jwsmith 122 May
#? 2
#? 1
total 0
#? 4
$
7 13:19 p2.c
Other Korn Additions:
String Length
• Length of string: ${#varname}
– Returns length of string stored in variable
• Example:
$ cat namelen
name="Pam Smallwood"
echo ${#name}
$ namelen
13
$
Other Korn Additions
• Forcing Command Execution
– In addition to the back quotes (graves)
`command`
– In Korn you can use:
$(command)
• Example:
$ name=$(whoami)
$ echo $name
small000
Sample .kshrc file
# Set command aliases
alias rm='rm -i '
alias rename='mv '
alias c clear
# Set environment variables
PATH=$PATH:.
PS1="$PWD[!] $ "
EDITOR=vi
# Export global variables
export PATH EDITOR PS1
# Set history variables
HISTSIZE=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 session1
Script started, file is session1
$ pwd
/export/home/small000
$ date
Thu May 22 19:34:25 MDT 2003
$ <CTRL-d>
Script done, file is session1
$ cat session1
$ pwd
/export/home/small000
$ date
Thu May 22 19:34:25 MDT 2003
script done on Thu May 22 19:34:29 2003
$