This little paper describes how to use the Korn Shell in the UNIX environment (very basic stuff).
At first, you have to create the file .profile in your home directory if it does not yet exist. That file should contain at least the following stuff:
PATH=/bin:/usr/bin:/usr/local/bin: EDITOR=/usr/bin/emacs SHELL=/bin/ksh export EDITOR
If you do not have such a file, some things may work but you will not have fun. Make sure it exists. To set (update) the environment variables type the following at the command line:
. ~/.profile
Alternatively, you can start a new session.
Within ksh there are two editing modes, emacs-mode and vi-mode. Since I like emacs I will explain that mode below.
In order to enable emacs-mode we set the environment variable VISUAL. Put the following line into your .profile:
VISUAL=$(whence emacs)
Update your .profile (see above) and emacs-mode is enabled.
Now I will show some important commands within emacs-mode.
| Command | Description |
|---|---|
| ESC b | Move one word backward |
| ESC f | Move one word forward |
| ESC h | Delete one word backward |
| ESC d | Delete one word forward |
| CTRL-A | Move to beginning of line |
| CTRL-E | Move to end of line |
| CTRL-K | Delete forward to end of line |
| CTRL-P | Move to previous line of history file |
| CTRL-N | Move to next line of history file |
| ESC < | Move to the first line of history file |
| ESC > | Move to last line of history file |
There are many more commands but in my opinion they are not so important.
Aliases are very popular and easy to use. An alias is defined at the command line or within the .profile file. It is simply a synonym for a command. OK, lets start with an example.
alias search=grep
Add this line to your .profile and whenever you type search you will start the program grep. That's it. It is also possible to define more complex aliases:
alias conn='netstat -a --tcp | grep ssh'
Notice that there are no spaces on either side of the equal sign.
Redirection is a very important thing and there is often much confusion about it. Therefore, I will give an overview.
| Redirector | Function |
|---|---|
| > file | Direct standard output to file |
| < file | Take standard input from file |
| cmd1 | cmd2 | Pipe |
| >> file | Append to file |
| n> file | Direct output file descriptor n to file |
| n< file | Set file as input file descriptor n |
| <&n | Duplicate standard input from file descriptor n |
| >&n | Duplicate standard output to file descriptor n |
The last four entries in the table above require an understanding of file descriptors. If you do not know what a file descriptor is you should read some documentation first.
A very basic fact is that every process has three file descriptors open:
How to save error messages from a program into a single file? OK, let's see an example.
program 2> file
All errors from program go into file.
program > file 2>&1
"2>&1" sends the standard error to the same place as standard output, to file.
I am sure you know that there is a powerful feature, filename completion and expansion. You have the choice between three possibilities within ksh
The first two items are important.
The TAB command is very important and you will often use it. OK, let's have an example.
Assume you want to change the current directory. The new one should be foobar. But there is another directory as well named forms. You type
cd fo TAB
and nothing happens. The reason is that fo matches both directories, foobar and forms. You have to type at least
cd foo TAB
and the directory name will be completed to foobar.
If you want to see some alternatives you use the command ESC *. Related to the example above, to show all directories (or ordinary) files beginning with fo type
cd fo ESC *
Note: ESC * does not execute a command.
Rosenblatt, Bill; Robbins, Arnold: Learning the Korn Shell, Second Edition, Beijing: O'Reilly & Associates, 2002
