Shell Scripting is the King of Devlopment

Shell Scripting

Shell scripting is a powerful process of automating day-to-day or regular activities on a Linux computer. It can be implemented on any AWS-hosted Linux machine or a Linux-hosted laptop. Here's an introduction to shell scripting and its commands:

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Creating a File in Linux

touch first-shell-script.sh

This command creates a new file named first-shell-script.sh.

To verify if the file has been created:

ls

The ls command lists all files and directories in the current directory.

Use ls -ltr for detailed information about files and directories, including:

1. Hard links

2. Owner and group

3. File size in bytes

4. Date and time of last modification

5. Name of the file/directory

To get detailed information about any command, use:

man ls

The man command provides a manual or description of the specified command.

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Editing Files

Use vim or vi to edit files. vim needs to be installed, whereas vi is pre-installed.

Example:

vim first-shell-script.sh

Inside the editor:

• Press Esc and then i to insert text.

• To save changes, press Esc and type :wq!.

• To exit without saving, use :q!.

To view the file content:

cat first-shell-script.sh

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Writing a Basic Shell Script

Start a script with a shebang:

#!/bin/bash

The shebang (#!) defines the interpreter for the script. Examples include:

• /bin/bash for Bash

• /bin/sh for SH

• /bin/ksh for KSH

Example script content:

#!/bin/bash
echo "My name is Piyush"

To execute the script:

sh first-shell-script.sh

or

./first-shell-script.sh

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Permissions with chmod

The chmod command changes file permissions. Permissions are divided into three categories:

1. Root user/administrator

2. Group

3. Others

Each permission is represented numerically:

• 4 = Read

• 2 = Write

• 1 = Execute

Example:

chmod 777 first-shell-script.sh

This grants read, write, and execute permissions to all users.

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Useful Commands

• mkdir <directory-name>: Create a directory.

• cd <directory-name>: Change directory.

• rm -rf <file/directory>: Force delete files or directories.

• history: View the history of all executed commands.

To write comments in shell scripts:

# This is a comment

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Debugging Mode

Enable debug mode in your script using:

set -x

Example:

set -x
echo "Print disk space"
df -h
echo "Print memory"
free -g

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Process Management

• ps -ef: List all running processes with detailed information.

• ps -ef | grep <keyword>: Filter processes containing a specific keyword.

• | (Pipe): Pass the output of one command as input to another command.

Example:

ps -ef | grep "amazon"

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Summary

• Creating and editing files: Using touch, vim, and cat.

• Permissions: Managed with chmod.

• Debugging and process management: Using set -x and ps -ef.

• Integration: The pipe (|) command connects outputs and inputs.

Mastering these commands and techniques makes shell scripting a valuable tool for Linux automation.

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