Quoth br...@lorf.org,
> On Tuesday, 14.04.09 at 22:13, Lennart Augustsson wrote:
>> So the right way to do this (like opening a file), is to try executing
>> it and let the OS tell you if it failed.
>
> I know, but the various functions that create processes don't help me
> know whether the program actually ran or not. For example,
>
>> createProcess (proc "nosuch" []) >>= \(_,_,_,ph) -> waitForProcess ph
>
> returns ExitCode 127. If I use the same code to run 'test', a C program
> that returns 127, I get the same thing.
Right, awkward problem. Don't know if it can be solved in a portable
way, but you (as author of a createProcess-like function) can use a pipe
from the forked process. The code demo I append works, given FFI support
for the POSIX functions it uses, but may not be appropriate for use with
GHC (I'm using nhc98.)
Donn
------------
spawn file cmd env = do
(e0, e1) <- pipe
-- F_CLOEXEC: close fd on (sucessful) exec.
fcntlSetFlag e1 F_CLOEXEC
t <- fork (fex e0 e1)
close e1
rx <- readFd e0 256
if null rx
then return t
else ioError (userError rx)
where
fex e0 e1 = do
close e0
catch (execve file cmd env)
(\ e -> writeFd e1 (ioeGetErrorString e))
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