1.sh

 
#!/bin/bash 
A=B 
export A
echo "PID for 1.sh before exec/source/fork:$$"
echo "1.sh: \$A is $A"
case $1 in
        exec)
                echo "using exec..."
                exec ./2.sh ;;
        source)
                echo "using source..."
                . ./2.sh ;;
        *)
                echo "using fork by default..."
                ./2.sh ;;
esac
echo "PID for 1.sh after exec/source/fork:$$"
echo "1.sh: \$A is $A"