[r] Get the column number in R given the column name

Possible Duplicate:
Get column index from label in a data frame

I need to get the column number of a column given its name.

Supose we have the following dataframe:

df <- data.frame(a=rnorm(100),b=rnorm(100),c=rnorm(100))

I need a function that would work like the following:

getColumnNumber(df,"b")

And it would return

[1] 2

Is there a function like that?

Thanks!