library("DescTools")

mainDir <- "~"
readExtension <- function()
{
  extFileName <- readline(prompt="Enter an extension file name: ")
  extFiledir <- file.path(mainDir, extFileName)
  if(file.exists(extFiledir) == FALSE) {
    dir.create(extFiledir)
  } else {
    unlink(extFiledir, recursive = TRUE)
  }
  fileList <- list.files(path = mainDir, pattern = extFileName, recursive = FALSE)
  index <- 1
  while(index<=length(fileList)) {
    strPosIndex <- StrPos(pattern = extFileName, fileList[index])
    if(is.na(strPosIndex) == FALSE) {
      file.copy(file.path(mainDir, fileList[index]), extFiledir)
    }
    index <- index + 1
  }
}