Intro to bash scripting and command line

My study resources are the Bash Scripting Tutorial article from freeCodeCamp and Introduction to Bash Guide from Devops Daily

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Basic Bash Commands

date: Displays the current date in the terminal

date
Thu Sep 24 12:04:57 EEST 2026

pwd: Displays the present working directory

pwd
/Users/mas/documents

ls: Lists the contents of the current directory

ls
images.jpeg folder file.txt

echo: Prints a string of text, or value of a variable to the terminal

echo "Hello world"
Hello world

cd: Change the directory to a different location.

 cd documents
~/documents$

mkdir: Create a new directory.

mkdir newFolder 
ls
newFolder GitHub		

touch: Create a new file.

touch file.txt

rm: Remove a file or directory.

rm file.txt

cp: Copy a file or directory.

 cp file.txt ~/documents/

mv: Move or rename a file or directory.

 mv file.txt ~/documents/newfile/

echo: Print text to the terminal.

echo "hello world"
hello world

cat: Concatenate and print the contents of a file.

cat file.txt

hello world,

this is an example

grep: Search for a pattern in a file.

grep "hello" file.txt

chmod: Change the permissions of a file or directory.

chmod u+x run_all.sh

sudo: Run a command with administrative privileges.

sudo [command]

df: Display the amount of disk space available.

df

history: Show a list of previously executed commands.

history

ps: Display information about running processes.

ps

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Bash Script File

you can create a Bash script without .sh you can start the file with a shebang (# + ! + path to Bash) like this :

#!/bin/bash

you can find the bash path using which bash command inside your terminal

First File

create run_all.sh file then add this script to it

#!/bin/bash

# print today's date
echo "Today is " `date` 

# asks for the path
echo -e "\n Enter the path to the directory" 
read the_path

# Lists the contents of the path
echo -e "\n Your path has the following filess and folders: "
ls $the_path

To make the script executable, assign execution rights to your user using this command:

chmod u+x run_all.sh

chmod changes file permissions for the current user, +x adds the execution rights to the current user and u is the current user

then you can run the script using ./run_all.sh

Variables and data types

# assign the value
 country=Egypt
# printing the var value
 echo $country 
Egypt

Variables names are case-sensitive, they must start with a letter or _ and cannot contain spaces or special characters

Input and output

The first input way is read that reads the user input and store it inside a variable

#!/bin/bash 

# asking for the name
echo "What's your name?" 
# reading the user input
read entered_name 
# prints the value with a message
echo -e "\nWelcome to bash tutorial" $entered_name

The second way is reading a file using while loops, the example reads the input.txt file content and prints it in the terminal

while read line
do
  echo $line
done < input.txt

yeah i know this is what cat does, practice in silence please

The third way is CLI arguments $1 for the first arg and $2 for the second arg

hello.sh:

#!/bin/bash
echo "Hello, $1!"

when we run it we need to add a first arg to make sure it works

 ./hello.sh shnawy
Hello, shnawy!

To display the output you use the echo command

# prints hello to terminal
echo "hello" 

# prints to the file
echo "This is some text." > output.txt 

# append the text on the end of the file
echo "More text." >> output.txt 

Conditional statements

I created a simple Bash script that use if and elif and else that asks the user to enter a number between 1 and 100 If they enter a number higher or lower than that it prints a message.

cond.sh

#!/bin/bash
echo "give me a number between 1-100"
read num

if [ $num -gt 100 ]; then 
echo "number is greater than 100"
elif [ $num -lt 1 ]; then
echo "numer is lower than 1"
else
echo " Your number is $num "
fi

There’s another shorthand for this using logical operators like -a AND operator , -o OR operator

cond.sh

#!/bin/bash
echo "give me a number betwean 1-100"
read num

if [ $num -gt 100 -o $num -lt 1 ]; then 
echo "number out of the range"
else
echo " Your number is $num "
fi

Looping and Branching

While loop

check for a condition and loop until the condition remains true

#!/bin/bash
i=1
while [[ $i -le 10 ]] ; do
   echo "$i"
  (( i += 1 ))
done
# prints from 1 to 10

For loop

Same idea as a while loop but you iterate over a list

#!/bin/bash
for i in {1..5}
do
    echo $i
done

Case statements

a cleaner and more organized alter to long if-else chain, you gave it a value and it compares it against a list of possible options once it gets a match it excute the code for that specific option and skip the other

fruit="apple"

# it checks for the match value for the fruit
# in the list of options to find apple
case $fruit in
    "banana")
        echo "This is a yellow fruit."
        ;;
    "apple")
        echo "This is a red fruit."
        ;;
    "orange")
        echo "This is an orange fruit."
        ;;
    *)
        echo "Unknown fruit."
        ;;
esac

"apple") is an option, ;; it’s like break it ends that case, *) is the else version for case statements, esac closes the block

Debug and Troubleshoot Bash Scripts

• Using set -x when you set it inside the script file the terminal will print each command before executing it

• Using set -e adding this at the beginning of the script will force the script to stop immediately if any command fail

• Using set -u tells Bash to throw an error and stop the script if it encounters an undeclared variable

• Run bash -n script.sh will read the file and report any syntax errors

• Manually using echo