# 🚀 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.).
    

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**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:
    

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

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**4\. Scheduling Scripts using Cron:**

**Cron Job Syntax:**

* `* * * * *` represents minute, hour, day, month, weekday.
    
* Example: `0 0 * * * /path/to/`[`script.sh`](http://script.sh) runs a script daily at midnight.
    

**Examples of Scheduling Cron Jobs:**

* Running a script every 5 minutes: `*/5 * * * * /path/to/`[`script.sh`](http://script.sh).
    
* Running a script from Monday to Friday at 6 am: `0 6 * * 1-5 /path/to/`[`script.sh`](http://script.sh).
    

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**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`.