Bash Scripting: The Complete Guide (From Zero to Advanced)

Bash (Bourne Again SHell) is one of the most important tools every developer, DevOps engineer, system administrator, and backend engineer must master. Bash is not just a command-line interface—it is a powerful scripting language used to automate systems, deploy applications, manage servers, and glue entire infrastructures together.

This article is a complete Bash scripting reference, covering everything from fundamentals to advanced scripting techniques.

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1. What Is Bash?

Bash is:

• A shell (command interpreter)
• A scripting language
• The default shell on most Linux systems
• Available on macOS and Windows (WSL, Git Bash)

Bash executes commands entered by the user or stored inside scripts.

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2. Bash vs Shell

• Shell is a general term for command interpreters (sh, zsh, fish)
• Bash is an enhanced version of the original Bourne Shell (sh)

• Bash adds:

  • Arrays
  • Command history
  • Job control
  • Advanced string manipulation

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3. Bash Script File Basics

A Bash script is a text file containing Bash commands.

File extension

script.sh

Shebang (Mandatory)

#!/bin/bash

This tells the OS which interpreter to use.

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4. Making a Script Executable

chmod +x script.sh

Run it:

./script.sh

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5. Comments in Bash

# This is a comment

No multi-line comment syntax exists natively.

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6. Variables in Bash

Variable Declaration

name="Farhad"
age=25

❗ No spaces around =.

Accessing Variables

echo $name
echo ${age}

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7. Environment Variables

export PATH=$PATH:/custom/path

View:

printenv

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8. Read User Input

read username
echo "Hello $username"

With prompt:

read -p "Enter name: " name

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9. Positional Parameters

./script.sh arg1 arg2

Inside script:

$0  # script name
$1  # first argument
$2  # second argument
$@  # all arguments
$#  # number of arguments

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10. Exit Codes

Every command returns a status code:

• 0 → success
• Non-zero → failure

echo $?

Exit manually:

exit 1

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11. Conditional Statements

if

if [ $age -gt 18 ]; then
  echo "Adult"
fi

if-else

if [ "$name" == "Ali" ]; then
  echo "Hello Ali"
else
  echo "Unknown user"
fi

elif

if [ $age -lt 18 ]; then
  echo "Minor"
elif [ $age -lt 60 ]; then
  echo "Adult"
else
  echo "Senior"
fi

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12. Comparison Operators

Numeric

• -eq equal
• -ne not equal
• -gt greater than
• -lt less than
• -ge greater or equal
• -le less or equal

String

• = equal
• != not equal
• -z empty
• -n not empty

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13. Logical Operators

[ condition1 ] && [ condition2 ]
[ condition1 ] || [ condition2 ]
! condition

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14. Case Statement

case $option in
  start)
    echo "Starting"
    ;;
  stop)
    echo "Stopping"
    ;;
  *)
    echo "Invalid option"
    ;;
esac

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15. Loops

for loop

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

Range:

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

---

while loop

while [ $count -lt 5 ]; do
  echo $count
  ((count++))
done

---

until loop

until [ $count -gt 5 ]; do
  echo $count
  ((count++))
done

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16. break and continue

break
continue

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17. Functions

my_function() {
  echo "Hello"
}

Call:

my_function

With arguments:

greet() {
  echo "Hello $1"
}
greet Farhad

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18. Return Values from Functions

return 0

Retrieve:

$?

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19. Arrays

arr=(apple banana orange)

Access:

echo ${arr[0]}

All elements:

echo ${arr[@]}

Length:

echo ${#arr[@]}

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20. Associative Arrays

declare -A user
user[name]="Farhad"
user[age]=25

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21. String Manipulation

str="Hello World"

Length:

${#str}

Substring:

${str:0:5}

Replace:

${str/World/Bash}

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22. Arithmetic Operations

((a=5+3))
echo $a

Or:

expr 5 + 3

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23. Command Substitution

date=$(date)

Or:

date=`date`

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24. Input / Output Redirection

Redirect output

ls > file.txt

Append:

ls >> file.txt

Redirect input

wc -l < file.txt

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25. Pipes

ps aux | grep root

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26. File Test Operators

-f file    # regular file
-d dir     # directory
-e file    # exists
-r file    # readable
-w file    # writable
-x file    # executable

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27. Signals and Traps

trap "echo Interrupted" SIGINT

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28. Debugging Bash Scripts

Run with debug mode:

bash -x script.sh

Enable inside script:

set -x

Stop:

set +x

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29. Error Handling

set -e

Exit on error.

Custom handling:

command || echo "Failed"

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30. Process Management

Background:

command &

Wait:

wait

PID:

$$

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31. Cron Jobs (Automation)

Edit cron:

crontab -e

Example:

0 2 * * * /path/script.sh

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32. Best Practices

• Always use #!/bin/bash
• Quote variables "${var}"
• Use set -euo pipefail
• Use functions
• Avoid hard-coded paths
• Log outputs

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33. Real-World Use Cases

• Deployment scripts
• Server monitoring
• Log rotation
• CI/CD pipelines
• Backup automation
• DevOps orchestration

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34. Final Thoughts

Bash scripting is not optional for serious developers and engineers. It is the backbone of Linux systems, cloud infrastructure, and DevOps workflows. Mastering Bash gives you control over the operating system itself.

If you understand Bash deeply, you control the machine—not the other way around.

Comments

[ak0047]

Thank you for sharing this article!
As a beginner with Bash scripting, I found it really helpful and practical.

[Farhad Rahimi Klie]

have a good job my friend