Bash Scripting Basics

Bash Scripting

Bash (short for “Bourne Again Shell”) is a command-line shell and scripting language commonly used on Unix-based operating systems like Linux and macOS. Bash scripts are sequences of commands and instructions that automate tasks and perform system administration tasks. Here, we’ll cover the basics of writing Bash scripts.

Writing Your First Bash Script

To create a Bash script, you need a text editor. You can use built-in editors like nano or more advanced ones like vim or Visual Studio Code. Let’s start with a simple “Hello World” example:

#!/bin/bash
# This is a comment

echo "Hello, World!"

Here’s what each part does:

#!/bin/bash: This is called a shebang, and it tells the system to use the Bash interpreter to run the script.

This is a comment: Comments start with # and are for documentation purposes.

echo “Hello, World!”: The echo command prints text to the standard output (usually the terminal).

Running a Bash Script

Make the script executable by running chmod +x scriptname.sh, where scriptname.sh is the name of your script.

Execute the script with ./scriptname.sh.

Variables

You can store and manipulate data using variables in Bash:

#!/bin/bash

name="Alice"
echo "Hello, $name!"
name="Alice": Declares a variable named name and assigns it the value "Alice."

"Hello, $name!": Uses the variable inside a string with double quotes. Bash will replace $name with the variable's value.

Input and Output

You can read user input and display output:

#!/bin/bash

echo "What's your name?"
read name
echo "Hello, $name!"
read name: Reads user input into the name variable.

Conditional Statements

You can use if statements for conditional execution:

#!/bin/bash

echo "Enter your age:"
read age

if [ "$age" -ge 18 ]; then
  echo "You're an adult."
else
  echo "You're a minor."
fi

if [ “$age” -ge 18 ]; then: Checks if the age is greater than or equal to 18.
else: Handles the case when the condition is not met.
fi: Ends the if statement.

Loops

Bash supports for and while loops:

bash

#!/bin/bash

# For loop
for i in {1..5}; do
  echo "Iteration $i"
done

# While loop
count=1
while [ $count -le 5 ]; do
  echo "Iteration $count"
  ((count++))
done

Functions

You can define functions to reuse code:

#!/bin/bash

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

greet "Alice"
greet "Bob"
greet() { ... }: Defines a function named greet that takes one argument.

greet "Alice": Calls the greet function with "Alice" as an argument.

Command-Line Arguments
You can access command-line arguments in a script:

bash
Copy code
#!/bin/bash

echo "Script name: $0"
echo "First argument: $1"
echo "Second argument: $2"

$0: The script’s name.
$1, $2, etc.: Command-line arguments.

Scripting is Powerful

Bash scripting is a versatile tool for automating tasks, managing files, and performing system administration on Unix-based systems. With the basics covered here, you can start writing your own Bash scripts to simplify and automate your workflow.

Useful Functions for Devs

Below are some bash functions tailored for software developers. These functions can be added to your bash profile (e.g., ~/.bashrc or ~/.bash_profile) so they’ll be available whenever you start a new terminal session.

Committing and Pushing Code to GitHub:

function git_push() {
    local message="$1"
    if [[ -z "$message" ]]; then
        echo "Commit message is required."
        return 1
    fi
    git add .
    git commit -m "$message"
    git push
}

Usage: `git_push “Your commit message”“

Scaffolding a New Express.js Project:

function create_express_project() {
    local project_name="$1"
    if [[ -z "$project_name" ]]; then
        echo "Project name is required."
        return 1
    fi
    npx express-generator "$project_name"
    cd "$project_name" && npm install
}

Usage: create_express_project your_project_name

Scaffolding a New Python Project:

function create_python_project() {
    local project_name="$1"
    if [[ -z "$project_name" ]]; then
        echo "Project name is required."
        return 1
    fi
    mkdir "$project_name"
    cd "$project_name"
    python -m venv venv
    source venv/bin/activate
    touch main.py
}

Usage: create_python_project your_project_name

Scaffolding a New Ruby Project:

function create_ruby_project() {
    local project_name="$1"
    if [[ -z "$project_name" ]]; then
        echo "Project name is required."
        return 1
    fi
    mkdir "$project_name"
    cd "$project_name"
    echo "source 'https://rubygems.org'" > Gemfile
    bundle install
    touch main.rb
}

Usage: create_ruby_project your_project_name

These functions streamline some common tasks in a developer’s workflow. For the git_push function, it’s a basic example, and you might want to extend or modify it according to your workflow, such as handling different branches, remotes, or even adding error checking before proceeding to each step.

For scaffolding functions, these are very basic and can be greatly expanded upon to suit your needs or your team’s project structure conventions. They serve as a starting point and can save a lot of time when starting new projects.

Remember to source your bash profile after adding these functions to it, by running source ~/.bashrc or source ~/.bash_profile, or by opening a new terminal session.

Reference

Cheatsheets

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