Shell Scripting Crash Course - Cheatsheet for beginners

This is a bash shell scripting which can be found on Unix, Linux and Mac. You can install bash on the Linux subsystem on Windows too.

the first line is #! /bin/bash because the bash program is in /bin/bash, you can know the path where the bash is by this command which bash.

print data or text on the screen 🔗

You can use echo Hello, World! or echo "Hello, world!".

Variables & Print out them 🔗

NAME = "Abanoub"
echo "My name is $NAME"

or you can use this

NAME = "Abanoub"
echo "My name is ${NAME}"

Get Data From User 🔗

read -p "Enter your name: " NAME
echo "Hello, $NAME!"

If Statement 🔗

The simple if statement syntax of bash script:

if ["$NAME" == "Abanoub"]
then
    echo "Yourname is Abanoub!"
fi

NOTE THAT: the end of if is fi the reverse letters of if.

The if else statement syntax in bash script:

if ["$NAME" == "Abanoub"]
then
    echo "Yourname is Abanoub!"
else
    echo "Yourname is NOT Abanoub"
fi

The else if (elif) condition statement syntax in bash scripting:

if ["$NAME" == "Abanoub"]
then
    echo "Yourname is Abanoub!"
elif ["$NAME" == "Jack"]
then
    echo "Yourname is Jack!"
else
    echo "Yourname is NOT Abanoub NOR Jack!"
fi

Logic Comparisons 🔗

You can use those operators:

and use them like this:

NUM1 = 3
NUM2 = 5
if ["$NUM!" -gt "$NUM2"]
then
    echo "$NUM1 is greater then $NUM2"
fi

File Conditions 🔗

These are the file condition flags:

and use them like this:

FILE = "test.txt"
if [ -f "$FILE" ]
then
    echo "$FILE is a file"
else
    echo "$FILE is NOT a file"
fi

Case Statement 🔗

Case is called switch case in other languages, and some modern languages call it when case such as Kotlin programming language.

Here is the case statement in bash scripting:

read -p "Are you 25? Y/N" ANSWER
case "$ANSWER" in
    [yY]|[yY][eE][sS])
        echo "Your age is mine :)"
        ;;
    [nN]|[nN][oO])
        echo "Nooo, your age is different than mine :("
        ;;
    *)
        echo "Please enter y/yes or n/no"
        ;;
    esac

Note that:

[nN] is a way of giving two probabilities small n or capital N.

[yY][eE][sS] is the word yes or YES or any combination of small and capital letters to compose a YeS word.

*) this is the default option in the case statement which is called default in other programming languages.

esac is the closing of the case statement as it is the reversed letters of case . This is the way of ending statements in bash script.

For Loop 🔗

NAMES = "Abanoub Jack John Smith"
for NAME in $NAMES
    do
    echo "Hello, $NAME"
done

Here is a script to rename all text files *.txt at once by a script:

FILES = $(ls *.txt)
NEW = "new"
for FILE in $FILES
    do
    echo "Renaming $FILE to new-$FILE"
    mv $FILE $NEW-$FILE
done

While Loop 🔗

Here is a while loop to read nfile.txt line by line.

LINE = 1
while read -r CURRENT_LINE
    do
    echo "$LINE: $CURRENT_LINE"
    ((LINE++))
done < "./nfile.txt"

Bash Script Function Syntax 🔗

function sayHello(){
    echo "Hello, World!"
}
sayHello

We created a function to print out Hello, World! and call it to occur!

Bash Script Functions with Parameters 🔗

Here is how to write a functions with params in NAMES = "Abanoub Jack John Smith" bash scripting:

function greet(){
    echo "Hello, I am $1 and I am $2"
}
greet "Abanoub" "25"

The $1 is the first parameter, and $2 is the second parameter. So when we call the function, we should specify the two parameters in the same order like this greet "Abanoub" "25". This means that "Abanoub" is the first param $1 and "25" is the second param $2.

Final Tips 🔗

Now, you learned the syntax of bash scripting, but you need to learn the bash commands (I will make a cheatsheet for bash commands later). You will use the bash commands in the bash scripting syntax to build the script you want to run automatically (terminal app).