Searching value from one dataframe into another dataframe in R?

I have one dataframe which has psno

psno - 20140200, 20137760

then search these value into another df

psno in 2 df

i want to do take each psno from 1df and searches it with each psno of 2df

and after that it finds the psno in 2df i want to apply ifelse?

Any Help is appreciated ??