Bash Scripting Learning Repository

Welcome to my Bash Scripting Learning Repository! This repository is designed for beginners to learn Linux Bash scripting from scratch and demonstrate practical scripting skills through real examples. It contains study notes (explanations of fundamental Bash concepts) ready-to-run scripts.

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Contents

• /notes folder contains study materials on various topics.
• /scripts folder contains codes with comments.

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Why This Repository is Useful

• Ideal for beginners learning Linux Bash scripting
• Demonstrates key concepts: variables, loops, conditionals, functions, environment variables
• Provides ready-to-run practical scripts for automation
• Implements safety practices (set -euo pipefail) and clear documentation

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Quick Start

1. Clone the repository:

git clone https://github.com/fitandfine/linux-scripting-repo
cd linux-scripting-repo

2. Make scripts executable:

chmod +x scripts/*.sh

or you can make individual script files executable as well with

cd scripts
chmod +x your_script.sh

3. Run a script:

./scripts/your_script.sh --help

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Bash Syntax Reference for Beginners

1. Shebang

Specifies the interpreter to run the script:

#!/usr/bin/env bash

2. Variables

# Assigning a variable
name="Alice"
# Accessing variable
echo "Hello $name"
# Exporting variable to child processes
export MY_VAR="123"

3. Command Line Arguments

$0  # script name
$1  # first argument
$2  # second argument
$@  # all arguments as separate words
$*  # all arguments as a single string
$#  # number of arguments
$!  # PID of last background process
$?  # the exit status of the most recently executed foreground command.
     A value of 0 means success. Any other value (from 1 to 255) means failure.

4. Conditionals

If statements

if [[ -n "$1" ]]; then  # non-empty string
  echo "Argument provided: $1"
elif [[ $1 -eq 0 ]]; then  # numeric comparison
  echo "Argument is zero"
else
  echo "No argument provided"
fi

• -n STRING $\rightarrow$ true if string is non-empty
• -f FILE $\rightarrow$ true if file exists and is a regular file

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Numeric operators:

• -eq $\rightarrow$ Equal to
• -ne $\rightarrow$ Not Equal to
• -lt $\rightarrow$ Less than
• -le $\rightarrow$ Less than or equal to
• -gt $\rightarrow$ Greater than
• -ge $\rightarrow$ Greater than or equal to

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• [[ ... ]] $\rightarrow$ recommended for condition tests

Case statements*

case $1 in
  start) echo "Starting service";;
  stop) echo "Stopping service";;
  *) echo "Unknown command";;  # Wild card pattern match (like default case in C)
esac

5. Loops

For loop

for i in {1..5}; do
  echo "Number $i"
done

While loop

count=1
while [[ $count -le 5 ]]; do
  echo "Count $count"
  ((count++))
done

Until loop

count=1
until [[ $count -gt 5 ]]; do
  echo "Count $count"
  ((count++))
done

6. Functions

my_function() {
  local name=$1
  echo "Hello $name"
}

my_function "Bob"

• Use local for variables inside functions
• Return values via echo and capture with var=$(my_function)

7. Input and Output

# Read input from user
read -p "Enter your name: " name
echo "Hello $name"

# Redirect output
echo "Hello" > file.txt      # overwrite
echo "World" >> file.txt     # append

# Redirect errors
command 2> error.log           # stderr
command > output.log 2>&1       # stdout + stderr

8. Environment Variables

echo $HOME     # user's home directory
echo $PWD      # current working directory
echo $USER     # username
echo $SHELL    # default shell
export MY_VAR="123"  # set environment variable

9. Special Variables

• $? → exit code of last command
• $$ → PID of current script
• $! → PID of last background process
• $0 → script name
• $* / $@ → all arguments
• $# → number of arguments

10. Command Substitution

files=$(ls *.txt)
echo $files

• Captures the output of a command and stores in a variable

11. Pipes

ls -l | grep ".txt"  # send output of ls to grep

• Chains commands so output of one becomes input of another

12. Combining Loops and Conditionals

#!/usr/bin/env bash
for file in *.log; do
  if [[ -s $file ]]; then  # check if file is non-empty
    echo "$file is not empty"
  fi
done

13. Safety and Best Practices

• Use set -euo pipefail to catch errors early
• Quote variables: "$var" to avoid word splitting
• Validate input arguments
• Provide --help usage messages in scripts
• Break scripts into functions for readability
• Test scripts with different scenarios

14. Useful Commands in Scripts

• grep → search text
• awk / sed → text processing
• cut → extract columns
• find → locate files
• xargs → construct commands from input
• rsync → copy/sync files efficiently

15. Example Script

#!/usr/bin/env bash
# Check if a file exists and print message
FILE=$1
if [[ -f "$FILE" ]]; then
  echo "$FILE exists"
else
  echo "$FILE does not exist"
fi

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For more bash scripting guide, read this as well:

Bash Scripting Guide

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Practice Basics here:

Basic Bash Scripting Practice

Tips for Beginners

• Always quote variables: "$var"
• Use set -euo pipefail for safe scripts
• Add comments and clear usage instructions
• Start small: automate basic tasks first
• Gradually add functions, loops, and argument handling

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Also check out these websites:

https://explainshell.com/ by Idan Kamara

https://github.com/idank/explainshell