Data

Tools

Indexes

Applications

Experiments

Awesome

An open API service indexing awesome lists of open source software.

https://github.com/miusarname2/bash_scriptformanagementandoptimisation

🚀 Welcome to my Linux adventure! 🐧 This repo is my Bash lab: from monitoring CPU and memory to automating temporary file cleanups, all part of my vacation learning path to master system administration. All part of my holiday learning path to mastering system administration - join and explore with me! 🌟
https://github.com/miusarname2/bash_scriptformanagementandoptimisation

bash bash-script learning shell shell-scripting

Last synced: about 2 months ago
JSON representation

🚀 Welcome to my Linux adventure! 🐧 This repo is my Bash lab: from monitoring CPU and memory to automating temporary file cleanups, all part of my vacation learning path to master system administration. All part of my holiday learning path to mastering system administration - join and explore with me! 🌟

Awesome Lists containing this project

README 

          
## How to get started with Bash scripting



## Running Bash commands from the command line



As mentioned above, the shell prompt looks like this:



```

[username@host ~]$

```



You can enter any command after the `$` sign and see the result in the terminal.



Generally, commands follow this syntax:



```

command [OPTIONS] arguments

```



Let's look at some basic bash commands and see their results. Don't forget to follow the instructions! :)



### Basic commands:



- **`date`**: Displays the current date.



    ````bash

    zaira@Zaira:~/shell-tutorial$ date

    Tue Mar 14 13:08:57 PKT 2023

    ```



- **`pwd`**: Show current working directory



    ````bash

    zaira@Zaira:~/shell-tutorial$ pwd

    /home/zaira/shell-tutorial

    ```



- **``ls`**: List the contents of the current directory



    ````bash

    zaira@Zaira:~/shell-tutorial$ ls

    check_plaindrome.sh count_odd.sh env log temp

    ```



- **`echo`**: Print a string or the value of a variable to the terminal



    ````bash

    zaira@Zaira@Zaira:~/shell-tutorial$ echo ‘Hello bash’

    Hello bash

    ```



You can always consult a command manual with the `man` command.



For example, the `ls` manual looks like this:



> Image



You can see the options for a command in detail using `man`.

## How to Create and Run Bash Scripts



### Script Naming Conventions



By naming convention, Bash scripts typically end with `.sh`. However, Bash scripts can run perfectly fine without the `.sh` extension.



### Adding the Shebang



Bash scripts begin with a shebang. The shebang is a combination of the `#` symbol and the `!` symbol, followed by the path to the Bash shell. This is the first line of the script. The shebang instructs the shell to execute the script using the Bash shell. It is simply an absolute path to the Bash interpreter.



Below is an example of a shebang declaration:



```bash

#!/bin/bash

```



You can find the path to your Bash shell (which may differ from the above) using the following command:



```bash

which bash

```



### How to Execute a Bash Script

# Using `chmod` and Running Scripts



- **`chmod`**: Modifies the file's permissions for the current user: `u`.

- **`+x`**: Grants execute permissions to the current user. This means the file owner can now run the script.



### Example:

`run_all.sh` is the file we want to execute.



You can execute the script using any of the following methods:



```bash

sh run_all.sh

```



```bash

bash run_all.sh

```



```bash

./run_all.sh

```

## Variables and Data Types in Bash



Variables allow you to store data. You can use variables to read, access, and manipulate data throughout a script.



In Bash, there are no strict data types. A variable can store numeric values, single characters, or strings.



### Using Variables in Bash



You can assign and use variable values in the following ways:



- **Assigning a value directly**:



    ```bash

    country=Pakistan

    ```



- **Assigning a value based on the output of a program or command** using command substitution. Note that `$` is required to access the value of an existing variable:



    ```bash

    same_country=$country

    ```



### Accessing the Value of a Variable



To access the value of a variable, prepend `$` to the variable name:



```bash

zaira@Zaira:~$ country=Pakistan

zaira@Zaira:~$ echo $country

Pakistan

zaira@Zaira:~$ new_country=$country

zaira@Zaira:~$ echo $new_country

Pakistan

```



# Input and Output in Bash Scripts



## Gathering Information



This section discusses methods to provide input to your scripts.



### Reading User Input and Storing it in a Variable



You can read user input using the `read` command.



```bash

#!/bin/bash



echo "What's your name?"



read entered_name



echo -e "\nWelcome to the Bash tutorial, $entered_name"

```



> Image



### Reading from a File



This code reads each line from a file called `input.txt` and prints it to the terminal. We'll explore `while` loops in more detail later in this article.



```bash

while read line

do

  echo $line

done < input.txt

```



### Command-Line Arguments



In a Bash script or function, `$1` denotes the first argument passed, `$2` denotes the second argument, and so on.



This script takes a name as a command-line argument and prints a personalised greeting:



```bash

echo "Hello, $1!"

```



For example, we supply `Zaira` as an argument to the script:



```bash

#!/bin/bash

echo "Hello, $1!"

```



# Displaying Output



Here are some methods for receiving output from scripts.



### Printing to the Terminal



```bash

echo "Hello, World!"

```



This prints the text "Hello, World!" to the terminal.



### Writing to a File



```bash

echo "This is some text." > output.txt

```



This writes the text "This is some text." to a file named `output.txt`. Note that the `>` operator overwrites a file if it already has content.



### Appending to a File



```bash

echo "More text." >> output.txt

```



This appends the text "More text." to the end of the `output.txt` file.



### Redirecting Output



```bash

ls > files.txt

```



This lists files in the current directory and writes the output to a file called `files.txt`. You can redirect the output of any command to a file this way.



## Basic Bash Commands (`echo`, `read`, etc.)



Below is a list of commonly used Bash commands:



- **`cd`**: Changes the directory.

- **`ls`**: Lists the contents of the current directory.

- **`mkdir`**: Creates a new directory.

- **`touch`**: Creates a new file.

- **`rm`**: Deletes a file or directory.

- **`cp`**: Copies a file or directory.

- **`mv`**: Moves or renames a file or directory.

- **`echo`**: Prints text to the terminal.

- **`cat`**: Concatenates and displays the contents of a file.

- **`grep`**: Searches for a pattern in a file.

- **`chmod`**: Changes file or directory permissions.

- **`sudo`**: Runs a command with administrative privileges.

- **`df`**: Shows available disk space.

- **`history`**: Displays a list of previously executed commands.

- **`ps`**: Shows information about running processes.



# Conditional Statements (`if/else`)



Expressions that produce a boolean result, either true or false, are called conditions. Various forms of conditionals include `if`, `if-else`, `if-elif-else`, and nested conditionals.



### Syntax



```bash

if [[ condition ]];

then

    statement

elif [[ condition ]]; then

    statement

else

    do this by default

fi

```



Logical operators such as `-a` (AND) and `-o` (OR) can be used for more complex comparisons.



```bash

if [ $a -gt 60 -a $b -lt 100 ]

```



### Example: Using `if`, `if-else`, and `if-elif-else`



Here's a Bash script that determines if a number entered by the user is positive, negative, or zero:



```bash

#!/bin/bash



echo "Please enter a number: "

read num



if [ $num -gt 0 ]; then

  echo "$num is positive"

elif [ $num -lt 0 ]; then

  echo "$num is negative"

else

  echo "$num is zero"

fi

```



### See it in Action 🚀



# Loops and Branching in Bash



## While Loop



`while` loops check if a condition exists and repeat the loop as long as the condition is `true`. A counter statement is required to control the loop's execution.



In the following example, `(( i += 1 ))` increments the value of `i`. The loop will execute exactly 10 times.



```bash

#!/bin/bash

i=1

while [[ $i -le 10 ]] ; do

   echo "$i"

   (( i += 1 ))

done

```



## For Loop



The `for` loop, like the `while` loop, allows statements to execute a specific number of times. The syntax and usage differ.



In this example, the loop iterates 5 times.



```bash

#!/bin/bash

for i in {1..5}

do

    echo $i

done

```



## Case Statements



In Bash, `case` statements are used to compare a given value against a list of patterns and execute a block of code based on the first matching pattern. The syntax for a `case` statement in Bash is as follows:



```bash

case expression in

    pattern1)

        # code to execute if expression matches pattern1

        ;;

    pattern2)

        # code to execute if expression matches pattern2

        ;;

    pattern3)

        # code to execute if expression matches pattern3

        ;;

    *)

        # code to execute if none of the above patterns match expression

        ;;

esac

```



### Example



```bash

fruit="apple"



case $fruit in

    "apple")

        echo "This is a red fruit."

        ;;

    "banana")

        echo "This is a yellow fruit."

        ;;

    "orange")

        echo "This is an orange fruit."

        ;;

    *)

        echo "Unknown fruit."

        ;;

esac

```



In this example, since the value of `fruit` is `"apple"`, the first pattern matches, and the block of code prints "This is a red fruit." If the value of `fruit` were `"banana"`, the second pattern would match, printing "This is a yellow fruit," and so on. If `fruit` does not match any specified pattern, the default case executes, printing "Unknown fruit."



# Activity 1



Create a script to monitor CPU and memory usage, sending alerts if they exceed a defined threshold.



# Activity 2



Automate the cleanup of temporary files older than seven days.