How To Execute a Command with a Shell Script in Linux

Introduction to Execute a Command

Shell is a command-line interpreter that allows the user to interact with the system. It is responsible for taking inputs from the user and displaying the output.

Shell scripts are a series of commands written in order of execution. These scripts can contain functions, loops, commands, and variables. Scripts are useful for simplifying a complex series of commands and repetitive tasks.

In this article, you will learn how to create and execute shell scripts for the command line in Linux.

Prerequisites to Execute a Command

To complete this tutorial, you will need:

• Familiarity with using the terminal.
• Familiarity with a text editor.
• Familiarity with commands like chmod, mkdir, and cd.

Getting Started

A shell script needs to be saved with the extension .sh.

The file needs to begin with the shebang line (#!) to let the Linux system know which interpreter to use for the shell script.

For environments that support bash, use:

#!/bin/bash

For environments that support shell, use:

#!/bin/sh

This tutorial assumes that your environment supports bash.

Shell scripts can also have comments to increase readability. A good script always contains comments that help a reader understand exactly what the script is doing and the reasoning behind a design choice.

Creating and Running a Basic Shell Script

You can create a shell script using the vi editor, a cat command, or a text editor.

For this tutorial, you will learn about creating a shell script with vi:

vi basic_script.sh

This starts the vi editor and creates a basic_script.sh file.

Then, press i on the keyboard to start INSERT MODE. Add the following lines:

#!/bin/bash
whoami
date

To save and exit the vi editor:

1. Press ESC
2. Type : (colon character)
3. Type wq
4. Press ENTER

Finally, you can run the script with the following command to Execute a Command:

bash basic_script.sh

You may get output that resembles the following:

root
Fri Jun 19 16:59:48 UTC 2020

Using Variables in Shell Scripts

Scripts can include user-defined variables. Add the following lines to the script:

#!/bin/bash
# This is a comment

# defining a variable
GREETINGS="Hello! How are you"
echo $GREETINGS

Run the script:

bash basic_script.sh

This prints out the value assigned to the variable:

Hello! How are you

Reading Input from the Command Line

Shell scripts can accept input from the command line using the read command. Add the following lines:

#!/bin/bash
echo "What is your name?"
read NAME
GREETINGS="Hello! How are you"
echo $NAME $GREETINGS

Output:

What is your name?
Sammy
Sammy Hello! How are you

Defining Functions to Execute a Command

Users can define their own functions in a script. Add the following lines:

#!/bin/bash
echo "What is the name of the directory you want to create?"
read NAME

echo "Creating $NAME ..."
mkcd ()
{
  mkdir "$NAME" 
  cd "$NAME"
}

mkcd
echo "You are now in $NAME"

Output:

What is the name of the directory you want to create?
test_dir
Creating test_dir ...
You are now in test_dir

Conclusion

In this article, you learned how to create and Execute a Command for the line in Linux.