You won't always want to re-type your Korn shell instructions each time you want to run then, so you may store them in a file:

Here's the file "hello_korn"


and I can run it as follows:


But I have to KNOW that's a Korn script to run it - if I just want to type its name at the command line, I come across various issues:


and even when I fix permissions:


Three things:

1. I should change permissions on the file to make it executable:
 chmod a+x hello_korn
or similar

2. I should specifiy at the top of the file that it is to be run under the Korn shell rather than any other, by adding a line
 #!/usr/bin/ksh

3. I might decide to change my path:
 export PATH=$PATH:.
but bear in mind that there may be security implications of adding any executable files you have in the current directory onto the list of executable syou may run.

It then works:



A new Korn shell doesn't just start up in isolation; rather, it starts up by reading in some initial settings from
 /etc/profile
 and $HOME/.profile
if it's a login shell, and then from a file named in $ENV. And if it's a shell which has been called in by another shell, it will inherit environment variables and functions which have been exported by that other shell.

Note the /etc/profile will usually contain directives to run additional shell startup scripts such as
 /etc/ksh.kshrc
 and $HOME/.kshrc

If a shell variable called HISTFILE is set, then the history will be reloaded from that file; if HISTFILE is not set, there's no re-loading of a previous session.


Like in Tcl, "everything is a command" in Ksh programming. In other words, as you analyse the syntax of the statements of the language you'll always find that, underlying everything else, you have a command name followed by a series of arguments. But there are several groups of commands:


Commands in this group are included within the shell program itself, and may vary somewhat from other commands with the same name in othe Unix or Linux shell programs (you have been warned now, right?)



Rather like the built in commands, these may vary in their Korn shell implementation to their implementation in other shells - although any that you use in the Bourne shell should wok directly here in ksh.



You can make up your own commands too, using the alias command


Although useful, you should take care not to rely on too many of your own aliases if you regularly move from one Korn shell environment to another - you need to know the basics.

The following aliases are built in to the Korn shell


unalias will let you delete an alias.


The majority - the vaste majority - of commands you need will be separate programs, and you'll find them on your computer / file system in the various directories listed in $PATH.


Even commands as fundamental as ls and cp will be found as separate programs.

If you need to find out what comes from where, have a look at the whence command


or if you prefer



You can define your own command (script) within your script - nested scripts within the same shell if you like - as a function. A sort of heavy-weight alias, if you like.


Let's see the funky file:



The set command allows lots of shell settings (switches) to be thrown.
-C noclobber
-n noexec (for checking)
-v verbose
-x xtrace - very useful for learning about how scripts work!
vi allows vi style command line editing

Environment:

CDPATH PATH EDITOR HISTFILE OLDPWD PPID PS1, 2 3 and 4 SECONDS




See also Linux Basics Course

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