I've found my mistake: I was calling readProcess cmd ["-p -t"] instead of readProcess cmd ["-p","-t"] Not sure what are the semantics of quotation in this case, though. And I'm pretty sure my analysis is wrong because of that :) -- Cp On Thu, Aug 11, 2011 at 16:05, Donn Cave wrote:

Quoth Charles-Pierre Astolfi ,

...

readProcess cmd [opt1,opt2] seems to execute the following: $ cmd "opt1" "opt2"

That is usually fine, but I'm using an external program that doesn't understand the quotes, so I need to execute instead: $ cmd opt1 opt2

How should I do that?

I think your analysis is wrong.  I don't know what to suggest, though if you follow up you probably should mention what platform you're running on.  Maybe you could devise a simple test program that illustrates the problem?

       Donn

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On Thu, Aug 11, 2011 at 11:29, Charles-Pierre Astolfi wrote:

I've found my mistake: I was calling readProcess cmd ["-p -t"] instead of readProcess cmd ["-p","-t"]

Not sure what are the semantics of quotation in this case, though. And I'm pretty sure my analysis is wrong because of that :)

It's quite simple: readProcess uses the low level exec*() series of functions under the hood. Quoting is assumed to have already been dealt with; every parameter is a separate String (or (char *) in the C API) and passed literally. Quoting is used at the shell level (and shell-based APIs such as system()) to enable the shell to correctly generate a list of literal (char *) parameters. In general, if an exec-style API takes a list of strings (e.g. C execve(), Haskell readProcess, Perl's multiple-parameter form of system), it's using the exec()-based API and you should pass argument strings exactly as you want the program to see them; if its a single string, it's using a system()-based API and you need to worry about quoting. In this case, the tip-off is that the argument list is a [String] and not simply a String. -- brandon s allbery allbery.b@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms