id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
5376	Quotation in System.Process.system for Windows	simonpj		"Wagnerdm writes: I had a bit of fun recently tracking down quoting issues with the ""`system`"" command in Windows. For the examples below, I'll consistently use ""`Windows> `"" as the beginning of some text sent to the Windows command prompt cmd.exe, and use ""`GHC> `"" as the beginning of some text sent to a ghci session running in cmd.exe with `System.Cmd` imported.

The situation is this: I want to hand off a command line which has both a possibly-quoted command name and a (definitely) quoted argument. For concreteness, let's use ""more"" as the command and ""foo.txt"" as the argument, so that you can follow along at home on your favorite Windows system.
{{{
Windows> echo foo > foo.txt
Windows> ""more"" ""foo.txt""
foo
}}}
All good so far. But:
{{{
GHC> system ""\""more\"" \""foo.txt\""""
'more"" ""foo.txt' is not recognized as an internal or external command, operable program or batch file.
ExitFailure 1
}}}
After some digging, I discovered that system is shipping out to cmd /c, and indeed:
{{{
Windows> cmd /c ""more"" ""foo.txt""
'more"" ""foo.txt' is not recognized as an internal or external command, operable program or batch file.
}}}
I don't know what the *right* fix is. However, after a bit of playing around, I discovered the following:
{{{
Windows> cmd /c """"more"" ""foo.txt""""
foo
GHC> system ""\""\""more\"" \""foo.txt\""\""""
foo
ExitSuccess
}}}
Wrapping commands with an extra pair of double-quotes this way seemed to give behavior matching the bare cmd.exe for all the examples I could think of, even ones I thought it would break. For example:
{{{
GHC> system ""\""more foo.txt\""""
foo
ExitSuccess
}}}
If this turns out to be the right thing to do, it's pretty easy to implement. In the `commandToProcess` function, at `libraries/process/System/Process/Internals.hs:455`, the change is just
{{{
-   return (cmd, translate cmd ++ ""/c "" ++ string)
+   return (cmd, translate cmd ++ ""/c \"""" ++ string ++ ""\"""")
}}}
(And in any case, the examples above should answer this amusing comment, immediately following those lines:
{{{
	-- We don't want to put the cmd into a single
	-- argument, because cmd.exe will not try to split it up.  Instead,
	-- we just tack the command on the end of the cmd.exe command line,
	-- which partly works.  There seem to be some quoting issues, but
	-- I don't have the energy to find+fix them right now (ToDo). --SDM
	-- (later) Now I don't know what the above comment means.  sigh.
}}}
Later, Brandon comments: What that comment means is that how CMD.EXE handles spaces is Windows-version-dependent.  On the other hand, I ''think'' it's mostly consistent between XP and Windows 7 --- and I feel sorry for anyone forced to use an older version. 
"	bug	new	low	7.6.2	libraries/process	7.0.4				Unknown/Multiple	Unknown/Multiple	None/Unknown