Basic Shell Commands – in Shell Scripting
Welcome to this comprehensive, student-friendly guide on basic shell commands in shell scripting! Whether you’re just starting out or looking to brush up on your skills, this tutorial is designed to make learning shell scripting fun and engaging. 😊
What You’ll Learn 📚
- Core concepts of shell scripting
- Key terminology explained simply
- Step-by-step examples from basic to advanced
- Common questions and troubleshooting tips
Introduction to Shell Scripting
Shell scripting is like giving your computer a to-do list. It’s a way to automate tasks by writing scripts using shell commands. Think of it as teaching your computer to do repetitive tasks for you, so you can focus on more important things.
Key Terminology
- Shell: A program that interprets commands and acts as an interface between the user and the operating system.
- Script: A file containing a series of commands that the shell can execute.
- Command: An instruction given to the shell to perform a specific task.
Starting with the Simplest Example
#!/bin/bash
echo "Hello, World!"This is the classic “Hello, World!” script. Let’s break it down:
#!/bin/bash: This line tells the system to use the Bash shell to execute the script.echo "Hello, World!": This command prints “Hello, World!” to the screen.
Progressively Complex Examples
Example 1: Listing Files
#!/bin/bash
lsThis script lists all files in the current directory:
ls: Lists files and directories.
file2.txt
directory1/
Example 2: Creating and Navigating Directories
#!/bin/bash
mkdir my_directory
cd my_directory
echo "Now in my_directory"This script creates a directory and navigates into it:
mkdir my_directory: Creates a new directory named my_directory.cd my_directory: Changes the current directory to my_directory.
Example 3: Conditional Statements
#!/bin/bash
if [ -f "file.txt" ]; then
echo "file.txt exists."
else
echo "file.txt does not exist."
fiThis script checks if a file exists:
if [ -f "file.txt" ]: Checks if file.txt is a file.then: Executes the following command if the condition is true.else: Executes the following command if the condition is false.
Example 4: Loops
#!/bin/bash
for i in 1 2 3 4 5
do
echo "Number: $i"
doneThis script loops through numbers 1 to 5:
for i in 1 2 3 4 5: Loops through the numbers.do: Begins the loop block.echo "Number: $i": Prints the current number.done: Ends the loop block.
Number: 2
Number: 3
Number: 4
Number: 5
Common Questions and Answers
- What is a shell script?
A shell script is a file containing a series of commands that the shell can execute. It’s used to automate tasks.
- How do I run a shell script?
Make the script executable with
chmod +x script.shand then run it with./script.sh. - Why use shell scripting?
Shell scripting automates repetitive tasks, saving time and reducing errors.
- What is
#!/bin/bash?This line, called a shebang, tells the system which interpreter to use to execute the script.
- How do I debug a shell script?
Use
bash -x script.shto run the script in debug mode, which shows each command before it executes. - Can shell scripts take input?
Yes, use
readto take input from the user. - What are common errors in shell scripting?
Common errors include syntax errors, incorrect file paths, and permission issues.
- How do I handle errors in a script?
Use
set -eto stop the script on errors or handle errors with conditional statements. - What is the difference between
shandbash?bashis an enhanced version ofshwith more features. - Can I use variables in shell scripts?
Yes, declare variables with
VAR=valueand use them with$VAR. - How do I comment in a shell script?
Use
#to add comments. - How do I pass arguments to a shell script?
Use
$1,$2, etc., to access arguments passed to the script. - What is a loop in shell scripting?
A loop executes a block of code multiple times. Common loops are
for,while, anduntil. - How do I create a function in a shell script?
Define a function with
function_name() { commands }and call it withfunction_name. - What is
exitin shell scripting?exitterminates the script. You can specify an exit status withexit 0for success orexit 1for failure. - How do I redirect output in a shell script?
Use
>to redirect output to a file and2>to redirect errors. - What is a pipe in shell scripting?
A pipe
|passes the output of one command as input to another. - How do I schedule a shell script?
Use
cronjobs to schedule scripts. - What is
chmod?chmodchanges file permissions, allowing you to make scripts executable. - How do I handle user input in a shell script?
Use
readto capture user input.
Troubleshooting Common Issues
If your script doesn’t run, check permissions with
ls -land ensure it’s executable withchmod +x script.sh.
If you see a “command not found” error, check for typos or ensure the command is installed on your system.
Remember, practice makes perfect! Try writing your own scripts to automate tasks you do often.
Practice Exercises
- Create a script that takes a user’s name as input and greets them.
- Write a script that checks if a directory exists and creates it if it doesn’t.
- Develop a script that counts the number of files in a directory.
For more information, check out the Bash Manual and Shell Scripting Guide.