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miusarname2 / repository
🚀 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! 🌟
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! :)
date: Displays the current date.
zaira@Zaira:~/shell-tutorial$ date
Tue Mar 14 13:08:57 PKT 2023
```
pwd: Show current working directory
zaira@Zaira:~/shell-tutorial$ pwd
/home/zaira/shell-tutorial
```
``ls`: List the contents of the current directory
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
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.
By naming convention, Bash scripts typically end with .sh. However, Bash scripts can run perfectly fine without the .sh extension.
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:
#!/bin/bash
You can find the path to your Bash shell (which may differ from the above) using the following command:
which bash
chmod and Running Scriptschmod: 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.run_all.sh is the file we want to execute.
You can execute the script using any of the following methods:
sh run_all.sh
bash run_all.sh
./run_all.sh
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.
You can assign and use variable values in the following ways:
Assigning a value directly:
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:
same_country=$country
To access the value of a variable, prepend $ to the variable name:
zaira@Zaira:~$ country=Pakistan
zaira@Zaira:~$ echo $country
Pakistan
zaira@Zaira:~$ new_country=$country
zaira@Zaira:~$ echo $new_country
Pakistan
This section discusses methods to provide input to your scripts.
You can read user input using the read command.
#!/bin/bash
echo "What's your name?"
read entered_name
echo -e "\nWelcome to the Bash tutorial, $entered_name"
Image
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.
while read line
do
echo $line
done < input.txt
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:
echo "Hello, $1!"
For example, we supply Zaira as an argument to the script:
#!/bin/bash
echo "Hello, $1!"
Here are some methods for receiving output from scripts.
echo "Hello, World!"
This prints the text "Hello, World!" to the terminal.
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.
echo "More text." >> output.txt
This appends the text "More text." to the end of the output.txt file.
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.
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.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.
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.
if [ $a -gt 60 -a $b -lt 100 ]
if, if-else, and if-elif-elseHere's a Bash script that determines if a number entered by the user is positive, negative, or zero:
#!/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
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.
#!/bin/bash
i=1
while [[ $i -le 10 ]] ; do
echo "$i"
(( i += 1 ))
done
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.
#!/bin/bash
for i in {1..5}
do
echo $i
done
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:
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
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."
Create a script to monitor CPU and memory usage, sending alerts if they exceed a defined threshold.
Automate the cleanup of temporary files older than seven days.
Selected from shared topics, language and repository description—not editorial ratings.
VikramNaik26 /
Welcome to my Bash-Scripting repository! 🚀 In this repository, I'm embarking on an exciting journey to master the art of Bash shell scripting. As a versatile and powerful tool, Bash offers endless possibilities for automating tasks, managing systems, and unleashing the full potential of the command line.