R dataframe: Select columns with title condition

Question

I have the following dataframe:

Ad Bd Ce
1  1  1
2  2  2
3  3  3

And i want to select columns that contains 'd' in the name (i don't want to use column indexes).

I thought about using grepl(), but don't know how to specify the 'x' argument:

new_data <- old_data[,which(grepl("d",x))]