Shell Script

What is Shell Scripting?

Shell scripts are interpreted not compiler and used in Linux and UNIX computer systems.

Most used shell scripting.
.sh = Bourne Shell .ksh = Korn Shell .bash = Bourne Again Shell
File extensions does not matter as long as the shabang(#!) is stated. (e.g. #!/bin/ksh)

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Which to choose between Bourne and Korn Shell?

Bourne Shell is better because implementing Korn Shell in scripting can be anything like real ksh, pdksh and some of which are just symlinks to some other shell that has a "ksh" personality. This can lead to weird differences in execution behaviour.

At least with bash that it has a single code base, and all it need to worry about is what (usually minimum) version of bash is installed. UNIX/LINUX programming to bash is more reliably consistent.

Features

Bash vs Kornshell

• Is much easier to set a prompt that displays the current directory. To do the same in Kornshell is hackish.
• Kornshell has associative arrays and Bash doesn't.
• Kornshell handles loop syntax a bit better. You can usally set a value in a Kornshell loop and have it availabe after the loop.
• Bash handles getting exit codes from pipes in a cleaner way.
• Kornshell has the print command which is way better than the echo command.
• Bash has tab completions.
• Kornshell has the r history command that allows to quickly rerun older commands.
• Kornshell has the syntax cd old new which replaces old with new in your directory and CD's over there. It's convenient when you have are in a directory called /foo/bar/barfoo/one/bar/bar/foo/bar and you need to cd /foo/barfoo/two/bar/bar/foo/bar. In Kornshell, you can simply do cd one two and be done with it. In Bash. you'd have to cd ../../../../two/bar/bar/foo/bar/barfoo/one/bar/bar/foo/bar

UNIX in 1990s is booming and Kornshell was the go-to shell of choice. Bash is now implemented on most UNIX system as well as on Linux. And there are simply more resources available for learning Bash and getting help than Kornshell. Bash is simply the shell of choice now, so if you've got to learn something, might as well go with that is popular.

Commands

• Show shell types in linux cat /etc/shells
• Show bash version bash --version

Sources
KSH vs. BASH
Use BASH(Bourne Again Shell) or Kornshell
Debugging BASH scripts on the command line
Basic Shell Scripting Cheat Sheet

Dennis James Matildo