Shell Scripting Basics

Shell scripting is a method to automate tasks in UNIX-like operating systems using shell scripts, which are text files containing a series of commands. bash (Bourne Again SHell) and ksh (Korn SHell) are two popular shells that support scripting, each with its own set of features, though they share many syntax and functionality similarities. Both shells provide programming constructs that allow conditional execution, loops, and functions, making them powerful tools for automation. Here, we'll cover some basics of shell scripting with a focus on similarities and key differences between bash and ksh.

Shebang

Both bash and ksh scripts typically start with a "shebang" line that specifies the interpreter to be used:

#!/bin/bash

#!/bin/ksh

This line tells the system to execute the script with bash or ksh respectively.

Variables

Variables in both shells are assigned without spaces, and their values are accessed using a dollar sign ($):

name="world"
echo "Hello, $name"

Both shells support local and environment variables, though their syntax for advanced features like arrays can differ slightly.

Conditional Statements

Both bash and ksh support if-else statements, though there are differences in how they handle certain test conditions and modern syntax extensions like [[ ]] for testing.

if [ "$name" == "world" ]; then
  echo "Hello, $name"
else
  echo "Unknown"
fi

Loops

Both shells support for, while, and until loops. The syntax is generally the same across both shells:

for i in 1 2 3; do
  echo "Number $i"
done

Functions

Functions in both shells are defined and used similarly:

greet() {
  echo "Hello, $1"
}
greet "world"