Linux Bash Scripting for Beginners

1. First Script

echo "Hello!"

2. Keyboard Input

echo "Enter your name"
read name
echo "Your name is $name"

3. Shell Menu

echo "Choose color"
select color in red green blue white
do
  break
done
echo "You chose $color"

4. For Loop

Example 1

for name in bob tom harry
do
 echo "Hello $name"
done 

Example 2

for i in {1..10}
do
 echo "$i"
done 

Example 3

for i in {1..10..2}
do
 echo "$i"
done 

5. If Statements

echo -e "Guess number:\c"
read guess
if [ $guess = 6 ]
 then
 echo "Correct"
elif [ $guess != 6 ]
 then
 echo "False"
fi

6. Lists

colors=(red blue green yellow)

for color in ${colors[*]}
do
  echo "$color"
done  

7. Strings

string="Ali"
echo $string # Ali
string2=${string:0:1}
echo $string2 # A

8. Functions

Example 1

function hello {
    echo "Hello"
}

hello # Hello

Example 2

function hello {
    echo "Hello $1"
}

hello "Ali"  # Hello Ali

Example 3

function hello {
    echo "Hello $1 and $2"
}

hello "Ali" "Reza" # Hello Ali and Reza

Example 4

X="global"

function hello {
    echo "Hello"
    local VAR="Hi"
    echo $VAR  # Hi
    echo $X    # global
}

hello 
echo $VAR #  (You'll see it does not actually outputs the variable)
echo $X   # global

9. Files

Read file

file="test.txt"
while read line; do
echo $line
done < $file

Create file and Add text to file

file="test.txt"
echo "this is a test">>$file
cat $file

Create file and remove before text if file is exist

file="test.txt"
if [ -f $file ]; then
  echo "File exists, removing"
  rm -r $file
fi  
echo "this is a test">>$file
cat $file