knitpost function from Jason Fisher's blog at http://jfisher-usgs.github.io/r/2012/07/03/knitr-jekyll/ - i just brought the function to lower case so that i can remember how to call it

knitpost.r

KnitPost <- function(input, base.url = "/") {
    require(knitr)
    opts_knit$set(base.url = base.url)
    fig.path <- paste0("figs/", sub(".Rmd$", "", basename(input)), "/")
    opts_chunk$set(fig.path = fig.path)
    opts_chunk$set(fig.cap = "center")
    render_jekyll()
    knit(input, envir = parent.frame())
}