R/findonpath.R

In UCANR-IGIS/uavimg: Drone Image Utilities

#' findonpath
#'
#' Searches for a file on the system environment path
#'
#' @param fn The filename to search for (without a path)
#' @param status Show messages
#' @param quote Enclose returned filename in quotes
#'
#' @note
#' This will return the first found occurence of file \code{fn}, searching 1) the current working directory, 2) the user's R 'home' directory, 
#' then 3) the directories on the operating system environment 'path' 
#' 
#' @return The full path and name of the found file, or NULL if not found
#'
#' @export

findonpath <- function(fn, status=TRUE, quote=TRUE) {
  
  if (file.exists(fn)) {
    if (.Platform$OS.type == "windows") {
      return(fn)
    } else {
      return(file.path(dirname(fn), basename(fn)))  
    }      
  }
  
  path <- Sys.getenv("PATH")
  if (path == "") {
    if (status) cat("Path environment variable not found \n")
    return(NULL)
  }
  
  if (.Platform$OS.type == "windows") {
    path.delim <- ";"
  } else {
    path.delim <- ":"      
  }
  
  path.dirs <- c(path.expand("~"), strsplit(path, path.delim, fixed = TRUE)[[1]])
  fn.with.path <- file.path(path.dirs, fn)
  fn.with.path.exists <- which(file.exists(fn.with.path))
  if (length(fn.with.path.exists)==0) {
    if (status) cat(fn, "not found anywhere on the path\n")
    return(NULL)
  } 
  fnReturn <- normalizePath(fn.with.path[fn.with.path.exists[1]])
  if (length(fn.with.path.exists) > 1 && status) {
    cat(cw(paste(length(fn.with.path.exists), "occurences of", fn, "found on path"), final.cr=T))
    cat(cw(paste("Returning ", fnReturn), final.cr=T))
  }
  if (quote) {
    return(shQuote(fnReturn))
  } else {
    return(fnReturn)   
  }
}