#5376: Quotation in System.Process.system for Windows
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Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.0.4
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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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.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5376>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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