IF Structure

What i have so far is: Code:

if(if something in search field){
do all this
}
else{
display all because first time run
}
As you see when People first run the program i wish for all books to be displayed which is taking place in the else{ } because the searchfield is undefined! however if then people click search with nothing in the search field i dont want all books to show but an error as they are searching for nothing. See where the above would trigger and show all.

its also important people can press "return" to submit as well and clicking the button so seeing if the the button is undefined is not an option! as if return is pressed it dont value the button being pressed. What are my options ?