sourcing specific function in bash not working

Question

I am trying to source specific function of a bash file. Please find below simplified loadfun.sh :-

function a(){
        echo "This is a"
}

function b(){
        echo "This is b"
}

function load(){
        echo "exporting $1"
        export -f $1
}

$@

Also, please find below execution sequence of commands :-

$cat loadfun.sh                             
function a(){                               
        echo "This is a"                    
}                                           

function b(){                               
        echo "This is b"                    
}                                           

function load(){                            
        echo "exporting $1"                 
        export -f $1                        
}                                           

$@                                          
$                                           
$                                           
$                                           
$sh loadfun.sh a                            
This is a                                   
$                                           
$                                           
$a                                          
bash: a: command not found                  
$                                           
$                                           
$sh loadfun.sh load a                       
exporting a                                 
$                                           
$                                           
$                                           
$a                                          
bash: a: command not found                  
$                                           

I am not sure why

export -f a

is not exporting function a.

Answer 1

Source your script rather than executing it, so that the definitions and the export take place in your current shell:

source loadfun.sh a

As an aside -- the .sh extension is misleading; since this uses bash-only functionality, it should be named loadfun.bash. (Using extensions is frowned on in general for executable scripts, but since this is intended to be loaded as a library, an extension is appropriate).

Answer 2

If you only want to set specific functions whilst sourcing the file then you could use a case statement

case $1 in   
a)
        a(){
                echo "This is a"
        }
;;
b)
        b(){
                echo "This is b"
        }
;;
*)
        echo error message
;;
esac

And call the script with

. ./script [function to export]