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Check for files

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Posted by Shaun Biggs   USA  (644 posts)  [Biography] bio
Date Tue 28 Jul 2009 02:31 AM (UTC)
Is there any way to check for a file before trying to use dofile() on it? Or, probably more usefully, is there any way to trap the error for when there is no file and do something instead of displaying something like the following?

Run-time error
World: Aardwolf - Balaam
Immediate execution
cannot open asdf.lua: No such file or directory
stack traceback:
        [C]: in function 'dofile'
        [string "Command line"]:1: in main chunk

It is much easier to fight for one's ideals than to live up to them.
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Posted by WillFa   USA  (525 posts)  [Biography] bio
Date Reply #1 on Tue 28 Jul 2009 02:50 AM (UTC)
Ooooh! I came up against this one 2 or 3 weeks ago!

if utils.readdir("C:\\path\\to\\file.lua") then
-- do stuff.

Using ReadDir (not re-add ir, there is no infra red support ;) ) with a fully qualified file path will either return the file name, or nil if not found.

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Posted by Nick Gammon   Australia  (21,677 posts)  [Biography] bio   Forum Administrator
Date Reply #2 on Tue 28 Jul 2009 03:03 AM (UTC)

Amended on Tue 28 Jul 2009 03:04 AM (UTC) by Nick Gammon

If you check out the help for dofile, it says:

Using dofile is the same as:

function dofile (filename)
  local f = assert (loadfile (filename))
  return f ()
end -- dofile

Thus, if you do loadfile, you will get back nil if it fails. If not, you call the resulting function (see under loadfile).

So, basically:

function my_dofile (filename)
  local f = loadfile (filename)
  if not f then
    print "sigh -- foiled again!"
    return nil
  end -- can't load it
  return f ()
end -- my_dofile

This is more comprehensive than merely testing for the presence of the file, this checks it can be loaded (ie. it is valid Lua code).

- Nick Gammon

www.gammon.com.au, www.mushclient.com
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