How to access command-line arguments in a shell script?

Accessing Command-Line Arguments in a Shell Script

In shell scripting, you can access the command-line arguments passed to your script using special variables. These variables are numbered, starting from $0 for the script name, and $1, $2, $3, and so on for the subsequent arguments.

Understanding the Special Variables

1. $0: This variable contains the name of the script itself.
2. $1, $2, $3, ..., $9: These variables represent the first, second, third, and up to the ninth command-line arguments, respectively.
3. $@: This variable represents all the command-line arguments as a single string, with each argument separated by a space.
4. $*: This variable also represents all the command-line arguments, but it treats them as a single string, without separating them.
5. $#: This variable contains the total number of command-line arguments, excluding the script name.

Here's a simple example to demonstrate how to access the command-line arguments:

#!/bin/bash

echo "Script name: $0"
echo "First argument: $1"
echo "Second argument: $2"
echo "All arguments: $@"
echo "Number of arguments: $#"

Assuming you save this script as my_script.sh, you can run it with some command-line arguments like this:

$ ./my_script.sh hello world

The output will be:

Script name: ./my_script.sh
First argument: hello
Second argument: world
All arguments: hello world
Number of arguments: 2

Handling a Variable Number of Arguments

Sometimes, you may not know the exact number of arguments that will be passed to your script. In such cases, you can use a loop to iterate through all the arguments:

#!/bin/bash

for arg in "$@"
do
    echo "Argument: $arg"
done

This script will print out each argument on a new line.

Accessing Arguments Beyond the Ninth

If you need to access arguments beyond the ninth, you can use the ${10}, ${11}, and so on. Here's an example:

#!/bin/bash

echo "First argument: $1"
echo "Tenth argument: ${10}"

Visualizing the Concept with a Mermaid Diagram

Here's a Mermaid diagram that illustrates the concept of accessing command-line arguments in a shell script:

In conclusion, accessing command-line arguments in a shell script is a fundamental skill that allows you to create more dynamic and versatile scripts. By understanding the different special variables and how to use them, you can write scripts that can adapt to various input scenarios and automate a wide range of tasks.