Mastering Unix Shell Scripting: A Quick and Efficient Guide

When it comes to Unix Shell scripting, there are numerous resources available that cater to different needs. However, it is quite common for these resources to focus solely on BASH. While BASH has its merits, it is important to recognize that BASH's landscape has significantly evolved over time, making it more efficient and user-friendly. This article aims to dispel some common misconceptions about BASH and provide a practical, quick-learning approach to mastering Unix Shell scripting.

Addressing Misconceptions About BASH

Several decades ago, certain limitations of BASH were indeed valid concerns. For instance, some have argued that BASH cannot handle decimal arithmetic or that it cannot return parameters from functions. While these statements were true at some point, they do not accurately reflect the current capabilities of BASH.

Bash now supports advanced arithmetic operations through the use of bc, a language for arbitrary precision mathematics. For example, the following script demonstrates how to perform decimal multiplication:

Define the input values:

luku11
luku22

Extract the integer parts of the decimal numbers:

int1${luku1//.*}
int2${luku2//.*}

Multiply the integer parts and calculate the result:

apu$((int1 * int2))
tulos$((luku1 / 10**${#luku1#*.} * 10**${#luku2#*.} * apu))

Output the result:

echo $tulos

This script, although simplified, demonstrates that BASH can handle decimal arithmetic with the help of bc. Additionally, when it comes to arithmetic operations, BASH is surprisingly fast, even when limited to integer-based calculations. Here is a more detailed example to address the multiplication of decimals:

Performing Decimal Multiplication with BASH

function kerro9  {
    because this script is simplified it cannot cope with all input - but the principles behind its immaculate brethren are so hard to grasp that here you are:
luku11
luku22
int1${luku1%%.*}
int2${luku2%%.*}
apu$((int1 * int2))
tulos$((luku1 * 10**-${#luku1#*.} * luku2 * 10**-${#luku2#*.} * apu))
echo $((tulos / 10**${#tulos#*.})).${tulos#*.}
}
kerro9 15.12345 -1.22222222222

As you can see, even though BASH is restricted to integer-based calculations, it can achieve relatively accurate results with some adjustments. Using bc for such calculations can further enhance the precision.

Returning Parameters from Functions in BASH

Another common misconception is that BASH cannot return parameters from functions. In reality, BASH's design is such that it is unnecessary to return parameters in many cases. However, if you need to return the result of a function, you can do so by exporting the variable within the function. Here is an example:

function get_number() {
    local x10
    echo $x
}
y$(get_number)
echo $y

This script demonstrates how to return a parameter from a function and assign it to a variable. While it is technically true that BASH does not directly support returning parameters, the language is flexible enough to facilitate this functionality in a user-friendly manner.

Practical Steps to Master BASH Scripting

To master BASH scripting, it is beneficial to set clear objectives and work towards them using scripts. Here is a step-by-step guide:

Step 1: Install/Configure a User

sudo useradd -d /home/USER_NAME USER_NAME

This command creates a new user with the specified home directory.

Step 2: Add a Password (if required)

sudo passwd USER_NAME

Alternatively, you can use the '-p' option in the 'useradd' command to set the password directly:

sudo useradd -d /home/USER_NAME -p PASSWORD USER_NAME

Step 3: Set Ownership and Permissions

sudo chown USER_NAME -R APP_DIRECTORY

This command ensures that the specified application directory is owned by the created user and is accessible to them.

Step 4: Automate Application Deployment

For a more comprehensive deployment process, you can use BASH scripts to automate steps such as downloading application packages, unpacking them, and installing them. For instance:

Download the application package:

wget 

Unpack the package:

tar -xvf app.tar.gz

Install the application:

sudo service app start

Automate the deployment process:

#!/bin/bash
# Download the application package
wget 
# Unpack the package
sudo tar -xvf app.tar.gz
# Install the application
sudo service app start

By following these steps, you can efficiently manage the deployment and orchestration of application servers using BASH scripts.

Conclusion

BASH scripting has evolved significantly over the years, addressing many of the limitations once associated with the language. With the advent of tools like bc and the flexibility of the scripting language itself, mastering BASH can be both quick and rewarding. By setting clear objectives and leveraging the power of BASH scripting, you can automate complex tasks and streamline your workflow.