TL;DR
Bash shell scripting is a powerful tool for automating repetitive tasks on Linux systems. This article introduces basic concepts of Bash scripting and demonstrates how to write simple scripts for automation. Whether you need to run a sequence of commands, monitor system resources, or schedule backups, Bash scripting can make these tasks more efficient.
Introduction
The Bash shell is a command-line interface (CLI) for Linux systems. It allows users to interact with the system, run commands, and perform various tasks. Bash shell scripting takes this a step further by enabling the creation of scripts that can automate complex and repetitive tasks.
Writing Your First Bash Script
Bash scripts are text files containing a series of commands to be executed by the Bash shell. Here’s how to write a basic script:
- Create a New Script File: Use a text editor like nano or vi to create a new file, such as myscript.sh.
- Add the Shebang Line: The first line of the script should be #!/bin/bash. This tells the system to use the Bash shell to interpret the script.
- Write Commands: Add the commands you want the script to run, one per line. For example:
echo “Hello, World!”
date
- Make the Script Executable: Run the command chmod +x myscript.sh to make the script executable.
- Run the Script: Execute the script with ./myscript.sh.
Variables and Parameters
Bash scripts can use variables to store values and parameters to accept input from the user. Here’s an example:
name=$1
echo “Hello, $name!”
Run the script with ./myscript.sh PureVoltage, and it will greet you with “Hello, PureVoltage!”
Conditional Statements
You can use if, elif, and else statements to create conditional logic:
if [ “$1” == “PureVoltage” ]; then
echo “Welcome, PureVoltage!”
else
echo “Unauthorized user!”
fi
Loops
Loops allow you to repeat a sequence of commands. A for loop example:
for file in *.txt; do
echo “Processing $file…”
done
Scheduling Scripts with Cron
You can schedule your scripts to run at specific intervals using Cron. To edit the crontab, use crontab -e and add a line like:
0 * * * * /path/to/myscript.sh
This will run the script every hour on the hour.
To setup your script or learn more about scheduling scripts with Cron check out our other article Linux Basics: Scheduling Tasks with Cron
Functions in Bash Scripts
Functions allow you to create reusable blocks of code. Here’s how to define and call a function:
function greet {
echo “Hello, $1!”
}
greet “PureVoltage”
User Input
You can prompt the user for input using the read command:
echo “Enter your name:”
read name
echo “Hello, $name!”
Error Handling
You can handle errors using exit codes and the trap command:
#!/bin/bash
set -e
trap “echo ‘An error occurred!’” ERR
# Your script commands here
Debugging
You can debug your scripts by running them with the -x option:
bash -x myscript.sh
Working with Files
You can read and write files within your script:
# Reading from a file
while read line; do
echo “$line”
done < file.txt
# Writing to a file
echo “Content” > file.txt
Advanced Automation Examples
Include some real-world examples of how Bash scripting can automate complex tasks, such as:
- System Monitoring: Writing a script that checks CPU, memory, and disk usage and sends alerts if thresholds are exceeded.
- Backup Automation: Creating a script that compresses important directories and copies them to a backup location on a schedule.
- User Management: Automating the process of adding, modifying, or deleting users across multiple systems.
Conclusion
Bash shell scripting is an essential skill for Linux administrators and users looking to automate tasks. With a basic understanding of script writing, variables, loops, and conditional statements, you can start creating powerful scripts to make your work more efficient.