A crash course on Bash / Shell scripting concepts

if statement

if [[ $1 == "123" ]]
then echo "Argument 1 equals to 123"
else
echo "Argument 1 does not equal to 123"
fi

inverted if statement

if ! [[ $1 == "123" ]]
then echo "Argument 1 does not equal to 123"
fi

regular expression (checking for number)

regex='^[0-9]+$'
if [[ $num =~ regex ]]
then echo "This is a valid number!"
fi

while loop

NUMBER=1

while [[ $NUMBER -le "20" ]]

do echo "The number ($NUMBER) is less than 20"

NUMBER=$((NUMBER + 1))

done

awk (separate by char)

LINE=this,is,a,test
echo "$LINE" | awk -F ',' '{print The first element is $1}'

functions

MyFunction testing123
function MyFunction {
                    echo $1
                  }

read a file

while read -r LINE
do echo "Line: $LINE"

done < /tmp/inputfile.txt

case statement

case $1 in

[1-2]*) echo "Number is between 1 and 2"

        ;;

[3-4]*) echo "Number is between 3 and 4"

        ;;

5) echo "Number is 5"

        ;;

6) echo "Number is 6"

        ;;

*) echo "Something else..."

        ;;

esac

for loop

for arg in $*

do echo $arg

done

arrays

myarray=(20 "test 123" 50)
myarray+=("new element")

for element in {$myarray[@]}
do echo $element
done

getting user input

echo Please enter how your age:

read userinput

echo You have entered $userinput!

executing commands within bash

DATE1=`date +%Y%m%d`

echo Date1 is: $DATE1

DATE2=$(date +%Y%m%d) # preferred way

echo Date2 is: $DATE2

To be continued...