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|
------------------------------------------------------------------------
--
-- rawSystem
--
-- This is a separate file #included into Haskell source, because
-- we use it in a few places in the GHC source tree.
--
------------------------------------------------------------------------
{- |
The computation @rawSystem cmd args@ runs the operating system command
whose file name is @cmd@, passing it the arguments @args@. It
bypasses the shell, so that @cmd@ should see precisely the argument
strings @args@, with no funny escaping or shell meta-syntax expansion.
(Unix users will recognise this behaviour
as @execvp@, and indeed that's how it's implemented.)
It will therefore behave more portably between operating systems than @system@.
The return codes are the same as for @system@.
-}
rawSystem :: FilePath -> [String] -> IO ExitCode
{- -------------------------------------------------------------------------
IMPORTANT IMPLEMENTATION NOTES
(see also libraries/base/cbits/rawSystem.c)
On Unix, rawSystem is easy to implement: use execvp.
On Windows it's more tricky. We use CreateProcess, passing a single
command-line string (lpCommandLine) as its argument. (CreateProcess
is well documented on http://msdn.microsoft/com.)
- It parses the beginning of the string to find the command. If the
file name has embedded spaces, it must be quoted, using double
quotes thus
"foo\this that\cmd" arg1 arg2
- The invoked command can in turn access the entire lpCommandLine string,
and the C runtime does indeed do so, parsing it to generate the
traditional argument vector argv[0], argv[1], etc. It does this
using a complex and arcane set of rules which are described here:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccelng/htm/progs_12.asp
(if this URL stops working, you might be able to find it by
searching for "Parsing C Command-Line Arguments" on MSDN. Also,
the code in the Microsoft C runtime that does this translation
is shipped with VC++).
Our goal in rawSystem is to take a command filename and list of
arguments, and construct a string which inverts the translatsions
described above, such that the program at the other end sees exactly
the same arguments in its argv[] that we passed to rawSystem.
This inverse translation is implemented by 'translate' below.
Here are some pages that give informations on Windows-related
limitations and deviations from Unix conventions:
http://support.microsoft.com/default.aspx?scid=kb;en-us;830473
Command lines and environment variables effectively limited to 8191
characters on Win XP, 2047 on NT/2000 (probably even less on Win 9x):
http://www.microsoft.com/windowsxp/home/using/productdoc/en/default.asp?url=/WINDOWSXP/home/using/productdoc/en/percent.asp
Command-line substitution under Windows XP. IIRC these facilities (or at
least a large subset of them) are available on Win NT and 2000. Some
might be available on Win 9x.
http://www.microsoft.com/windowsxp/home/using/productdoc/en/default.asp?url=/WINDOWSXP/home/using/productdoc/en/Cmd.asp
How CMD.EXE processes command lines.
Note: CreateProcess does have a separate argument (lpApplicationName)
with which you can specify the command, but we have to slap the
command into lpCommandLine anyway, so that argv[0] is what a C program
expects (namely the application name). So it seems simpler to just
use lpCommandLine alone, which CreateProcess supports.
----------------------------------------------------------------------------- -}
#ifndef mingw32_TARGET_OS
rawSystem cmd args =
withCString cmd $ \pcmd ->
withMany withCString (cmd:args) $ \cstrs ->
withArray0 nullPtr cstrs $ \arr -> do
status <- throwErrnoIfMinus1 "rawSystem" (c_rawSystem pcmd arr)
case status of
0 -> return ExitSuccess
n -> return (ExitFailure n)
foreign import ccall unsafe "rawSystem"
c_rawSystem :: CString -> Ptr CString -> IO Int
#else
-- On Windows, the command line is passed to the operating system as
-- a single string. Command-line parsing is done by the executable
-- itself.
rawSystem cmd args = do
-- NOTE: 'cmd' is assumed to contain the application to run _only_,
-- as it'll be quoted surrounded in quotes here.
let cmdline = translate cmd ++ concat (map ((' ':) . translate) args)
withCString cmdline $ \pcmdline -> do
status <- throwErrnoIfMinus1 "rawSystem" (c_rawSystem pcmdline)
case status of
0 -> return ExitSuccess
n -> return (ExitFailure n)
translate :: String -> String
translate str@('"':_) = str -- already escaped.
-- ToDo: this case is wrong. It is only here because we
-- abuse the system in GHC's SysTools by putting arguments into
-- the command name; at some point we should fix it up and remove
-- the case above.
translate str = '"' : snd (foldr escape (True,"\"") str)
where escape '"' (b, str) = (True, '\\' : '"' : str)
escape '\\' (True, str) = (True, '\\' : '\\' : str)
escape '\\' (False, str) = (False, '\\' : str)
escape c (b, str) = (False, c : str)
-- See long comment above for what this function is trying to do.
--
-- The Bool passed back along the string is True iff the
-- rest of the string is a sequence of backslashes followed by
-- a double quote.
foreign import ccall unsafe "rawSystem"
c_rawSystem :: CString -> IO Int
#endif
|
