fread clearer 'file doesn't exist' message. Closes #486.

R/fread.R

@@ -46,8 +46,9 @@ fread <- function(input="",sep="auto",sep2="auto",nrows=-1L,header="auto",na.str
  # In text mode on Windows-only, R doubles up \r to make \r\r\n line endings. mode="wb" avoids that. See ?connections:"CRLF"
  input = tt
  } else if (input == "" || length(grep('\\n|\\r', input)) > 0) {
- # if text input
+ # text input
  } else if (!file.exists(input)) {
+ if (length(grep(' ', input)) == 0) stop("File '",input,"' does not exist. Include one or more spaces to consider the input a system command.")
  tt = tempfile()
  on.exit(unlink(tt), add = TRUE)
  if (.Platform$OS.type == "unix") {

README.md

@@ -35,6 +35,8 @@
  * doubled quotes ("") inside quoted fields including if immediately followed by an embedded newline. Thanks to James Sams for reporting, [#489](https://github.com/Rdatatable/data.table/issues/489). 
  * quoted fields with embedded newlines in the lines used to detect types, [#810](https://github.com/Rdatatable/data.table/issues/810). Thanks to Vladimir Sitnikov for the scrambled data file which is now included in the test suite.
  * when detecting types in the middle and end of the file, if the jump lands inside a quoted field with (possibly many) embedded newlines, this is now detected.
+ * if the file doesn't exist the error message is clearer ([#486](https://github.com/Rdatatable/data.table/issues/486))
+ * system commands are now checked to contain at least one space
 
  6. `as.data.table.list` with list input having 0-length items, e.g. `x = list(a=integer(0), b=3:4)`. `as.data.table(x)` recycles item `a` with `NA`s to fit the length of the longer column `b` (length=2), as before now, but with an additional warning message that the item has been recycled with `NA`. Closes [#847](https://github.com/Rdatatable/data.table/issues/847). Thanks to @tvinodr for the report. This was a regression from 1.9.2.
 

inst/tests/tests.Rraw

@@ -5566,10 +5566,7 @@ test(1451.6, ans1[c(3,3)], fans2(DT, c("V3", "V3"))) # using duplicate co
 test(1451.7, shallow(DT, integer(0)), null.data.table()) # length-0 input work as intended as well.
 test(1451.8, shallow(DT, character(0)), null.data.table()) # length-0 input work as intended as well.
 
-
-# > fread("notexist.csv")
-# sh: 1: nonfile.csv: not found
-# Error in fread("nonfile.csv") : File is empty: /dev/shm/file54e46ccdb63 
+test(1452, fread("notexist.csv"), error="File 'notexist.csv' does not exist. Include one or more spaces to consider the input a system command.")
 
 
 ##########################