🚀 Day 4 - Bash Scripting -2 #90DaysOfDevOps 🚀

1. Bash Scripting Basics:

What is Bash Scripting? Bash scripting involves creating a sequence of commands executed by the Bash shell, enhancing automation and repeatability.

Advantages of Bash Scripting:

• Facilitates system administration tasks.

• Efficient management of system resources.

• Automates routine tasks, improving productivity.

Where can Bash Scripting be Used? Bash scripting finds applications in databases, web servers, cloud services, and various other environments.

Bash and Shell: Bash, the default shell for Unix/Linux, executes commands read from input devices like keyboards.

Basic Bash Commands:

• date: Displays the current date.

• pwd: Shows the present working directory.

• ls: Lists the contents of the current directory.

• echo: Prints text to the terminal.

• cd: Changes the directory.

• mkdir: Creates a new directory.

• touch: Creates a new file.

• rm: Removes a file or directory.

• cp: Copies a file or directory.

• mv: Moves or renames a file or directory.

• grep: Searches for a pattern in a file.

• chmod: Changes the permissions of a file or directory.

• sudo: Executes a command with administrative privileges.

Adding the Shebang: Bash scripts start with a shebang (#!/bin/bash), followed by the Bash shell path.

---

2. Variables and Data Types:

Variable Naming Conventions:

• Variables start with a letter or underscore.

• They can contain letters, numbers, and underscores.

• Case-sensitive and descriptive names are recommended.

• Avoid using reserved keywords as variable names.

Input and Output in Bash Scripts:

• Reading user input using the read command.

• Reading from files (< input.txt).

• Command-line arguments ($1, $2, etc.).

---

3. Conditional Statements and Looping:

Conditional Statements:

• Using if/else for conditional execution.

• Example: if [ $a -gt 60 -a $b -lt 100 ].

Looping:

• while loop example:

bashCopy code#!/bin/bash
i=1
while [[ $i -le 10 ]]; do
    echo "$i"
    ((i += 1))
done

---

4. Scheduling Scripts using Cron:

Cron Job Syntax:

• * * * * * represents minute, hour, day, month, weekday.

• Example: 0 0 * * * /path/to/script.sh runs a script daily at midnight.

Examples of Scheduling Cron Jobs:

• Running a script every 5 minutes: */5 * * * * /path/to/script.sh.

• Running a script from Monday to Friday at 6 am: 0 6 * * 1-5 /path/to/script.sh.

---

5. Debugging and Troubleshooting Bash Scripts:

Debugging Techniques:

• Use set -x to trace execution.

• Check exit codes ($?).

• Utilize echo statements for debugging.

• Use set -e to exit immediately on error.

Troubleshooting Cron Jobs:

• Verify logs located at /var/log/syslog.