If Else in KornShell

#!/bin/ksh
#prompt the user to enter an input
print -n "enter the number of children you have :"
read numberofchildren
if ( (( numberofchildren>0 )) &&((numberofchildren<=1)) ); then #the space after the ( and before the ) is important

print "you have one children"
else
print "you have more than one children"

fi

If statement in Kornshell

#!/bin/ksh
#prompt the user to enter a number
print -n "Enter your age: "
read age
if ((age >= 18))
then
print "Vote"
fi
#operators are ==,!=,>,<,>=,<=

Install ZShell ,KornShell and CShell on Lubuntu 19.10

 sudo apt install zsh ksh csh

Install kornshell ,CShell and ZShell on Fedora 31

sudo dnf install ksh csh zsh