Weird problem with function ls or system("ls...")

[John W. Eaton]

On 28-Jul-2009, Christian Weickhmann wrote:

| I stumbled over a weird problem using octave to read data from files.
| 
| When I do an ls() or system("ls ...") in octave where no file matches my 
search 
| pattern, instead of returning an empty set, octave gives me a "No such file 
or 
| directory".
| 
| Example:
| 
| octave> mkdir test # create empty dir
| octave> ls
| # Works, no output
| ovtave> ls("*")
| # Works too, no output

That's not what I see.  Instead, I see following error:

  ls: cannot access *a*: No such file or directory
  error: ls: command exited abnormally with status 2
  error: called from:
  error:   /usr/share/octave/3.2.0/m/miscellaneous/ls.m at line 66, column 2

| octave> ls("*a*")
| ls: Zugriff auf *a* nicht möglich: No such file or directory
| error: ls: command exited abnormally with status 2
| error: called from:
| error:   /usr/share/octave/3.2.0/m/miscellaneous/ls.m at line 66, column 2
| 
| To be sure I looked into ls.m and found, that it's no magic at all: ls -> 
| system("ls ..."). So i tried
| 
| octave:> system("ls *a*")
| ls: Zugriff auf *a* nicht möglich: No such file or directory
| ans =  2
| 
| I know, I can catch that with a try/catch block. So I would not directly call 
| it a bug. But it's annoying. Frankly, it took me 1 hour to find what is 
causing 
| the problem. See, if you have a lot of data, and some record just doesn't 
| exist, you might want him to continue just fine... ;)
| 
| But it would be so much more intuitive, if worked just like in the ls * case, 
| as bash's ls also gives you an empty set. I assume that this is not intended, 
| because he obviously tries to access a file named "*a*".

There is no such thing as "bash's ls".  The ls command is a separate
program, not a part of bash.  And I'm not sure what you mean that it
also gives you an empty set.  Here is what I see in an empty directory:

  $ mkdir foo
  $ cd foo
  $ ls *
  ls: cannot access *: No such file or directory
  $ ls *a*
  ls: cannot access *a*: No such file or directory

This is not surprising since Octave just uses system to invoke ls.  So
the results should be the same.

FWIW, I think this behavior is also consistent with the way Matlab works.

Maybe you want to use dir instead of ls in your Octave program?

jwe