Portability | non-portable (requires concurrency) |
---|---|
Stability | experimental |
Maintainer | libraries@haskell.org |
System.Process
Description
Operations for creating and interacting with sub-processes.
- createProcess :: CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle)
- shell :: String -> CreateProcess
- proc :: FilePath -> [String] -> CreateProcess
- data CreateProcess = CreateProcess {}
- data CmdSpec
- data StdStream
- = Inherit
- | UseHandle Handle
- | CreatePipe
- data ProcessHandle
- runCommand :: String -> IO ProcessHandle
- runProcess :: FilePath -> [String] -> Maybe FilePath -> Maybe [(String, String)] -> Maybe Handle -> Maybe Handle -> Maybe Handle -> IO ProcessHandle
- runInteractiveCommand :: String -> IO (Handle, Handle, Handle, ProcessHandle)
- runInteractiveProcess :: FilePath -> [String] -> Maybe FilePath -> Maybe [(String, String)] -> IO (Handle, Handle, Handle, ProcessHandle)
- readProcess :: FilePath -> [String] -> String -> IO String
- readProcessWithExitCode :: FilePath -> [String] -> String -> IO (ExitCode, String, String)
- system :: String -> IO ExitCode
- rawSystem :: String -> [String] -> IO ExitCode
- showCommandForUser :: FilePath -> [String] -> String
- waitForProcess :: ProcessHandle -> IO ExitCode
- getProcessExitCode :: ProcessHandle -> IO (Maybe ExitCode)
- terminateProcess :: ProcessHandle -> IO ()
- interruptProcessGroupOf :: ProcessHandle -> IO ()
Running sub-processes
createProcess :: CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle)Source
This is the most general way to spawn an external process. The
process can be a command line to be executed by a shell or a raw command
with a list of arguments. The stdin, stdout, and stderr streams of
the new process may individually be attached to new pipes, to existing
Handle
s, or just inherited from the parent (the default.)
The details of how to create the process are passed in the
CreateProcess
record. To make it easier to construct a
CreateProcess
, the functions proc
and shell
are supplied that
fill in the fields with default values which can be overriden as
needed.
createProcess
returns (mb_stdin_hdl, mb_stdout_hdl, mb_stderr_hdl, p)
,
where
- if
std_in == CreatePipe
, thenmb_stdin_hdl
will beJust h
, whereh
is the write end of the pipe connected to the child process'sstdin
. - otherwise,
mb_stdin_hdl == Nothing
Similarly for mb_stdout_hdl
and mb_stderr_hdl
.
For example, to execute a simple ls
command:
r <- createProcess (proc "ls" [])
To create a pipe from which to read the output of ls
:
(_, Just hout, _, _) <- createProcess (proc "ls" []){ std_out = CreatePipe }
To also set the directory in which to run ls
:
(_, Just hout, _, _) <- createProcess (proc "ls" []){ cwd = Just "\home\bob", std_out = CreatePipe }
shell :: String -> CreateProcessSource
Construct a CreateProcess
record for passing to createProcess
,
representing a command to be passed to the shell.
proc :: FilePath -> [String] -> CreateProcessSource
Construct a CreateProcess
record for passing to createProcess
,
representing a raw command with arguments.
data CreateProcess Source
Constructors
CreateProcess | |
Fields
|
Constructors
ShellCommand String | a command line to execute using the shell |
RawCommand FilePath [String] | the filename of an executable with a list of arguments |
Constructors
Inherit | Inherit Handle from parent |
UseHandle Handle | Use the supplied Handle |
CreatePipe | Create a new pipe. The returned
|
data ProcessHandle Source
Specific variants of createProcess
runCommand :: String -> IO ProcessHandleSource
Runs a command using the shell.
Arguments
:: FilePath | Filename of the executable |
-> [String] | Arguments to pass to the executable |
-> Maybe FilePath | Optional path to the working directory |
-> Maybe [(String, String)] | Optional environment (otherwise inherit) |
-> Maybe Handle | Handle to use for |
-> Maybe Handle | Handle to use for |
-> Maybe Handle | Handle to use for |
-> IO ProcessHandle |
Runs a raw command, optionally specifying Handle
s from which to
take the stdin
, stdout
and stderr
channels for the new
process (otherwise these handles are inherited from the current
process).
Any Handle
s passed to runProcess
are placed immediately in the
closed state.
Note: consider using the more general createProcess
instead of
runProcess
.
runInteractiveCommand :: String -> IO (Handle, Handle, Handle, ProcessHandle)Source
Runs a command using the shell, and returns Handle
s that may
be used to communicate with the process via its stdin
, stdout
,
and stderr
respectively. The Handle
s are initially in binary
mode; if you need them to be in text mode then use hSetBinaryMode
.
Arguments
:: FilePath | Filename of the executable |
-> [String] | Arguments to pass to the executable |
-> Maybe FilePath | Optional path to the working directory |
-> Maybe [(String, String)] | Optional environment (otherwise inherit) |
-> IO (Handle, Handle, Handle, ProcessHandle) |
Runs a raw command, and returns Handle
s that may be used to communicate
with the process via its stdin
, stdout
and stderr
respectively.
For example, to start a process and feed a string to its stdin:
(inp,out,err,pid) <- runInteractiveProcess "..." forkIO (hPutStr inp str)
The Handle
s are initially in binary mode; if you need them to be
in text mode then use hSetBinaryMode
.
Arguments
:: FilePath | command to run |
-> [String] | any arguments |
-> String | standard input |
-> IO String | stdout |
readProcess forks an external process, reads its standard output strictly, blocking until the process terminates, and returns the output string.
Output is returned strictly, so this is not suitable for interactive applications.
Users of this function should compile with -threaded
if they
want other Haskell threads to keep running while waiting on
the result of readProcess.
> readProcess "date" [] [] "Thu Feb 7 10:03:39 PST 2008\n"
The arguments are:
- The command to run, which must be in the $PATH, or an absolute path
- A list of separate command line arguments to the program
- A string to pass on the standard input to the program.
Arguments
:: FilePath | command to run |
-> [String] | any arguments |
-> String | standard input |
-> IO (ExitCode, String, String) | exitcode, stdout, stderr |
readProcessWithExitCode creates an external process, reads its
standard output and standard error strictly, waits until the process
terminates, and then returns the ExitCode
of the process,
the standard output, and the standard error.
readProcess
and readProcessWithExitCode
are fairly simple wrappers
around createProcess
. Constructing variants of these functions is
quite easy: follow the link to the source code to see how
readProcess
is implemented.
system :: String -> IO ExitCodeSource
Computation system cmd
returns the exit code produced when the
operating system runs the shell command cmd
.
This computation may fail with
-
PermissionDenied
: The process has insufficient privileges to perform the operation. -
ResourceExhausted
: Insufficient resources are available to perform the operation. -
UnsupportedOperation
: The implementation does not support system calls.
On Windows, system
passes the command to the Windows command
interpreter (CMD.EXE
or COMMAND.COM
), hence Unixy shell tricks
will not work.
rawSystem :: String -> [String] -> IO ExitCodeSource
The computation
runs the operating system command
rawSystem
cmd argscmd
in such a way that it receives as arguments the args
strings
exactly as given, with no funny escaping or shell meta-syntax expansion.
It will therefore behave more portably between operating systems than system
.
The return codes and possible failures are the same as for system
.
showCommandForUser :: FilePath -> [String] -> StringSource
Given a program p
and arguments args
,
showCommandForUser p args
returns a string suitable for pasting
into sh (on POSIX OSs) or cmd.exe (on Windows).
Process completion
waitForProcess :: ProcessHandle -> IO ExitCodeSource
Waits for the specified process to terminate, and returns its exit code.
GHC Note: in order to call waitForProcess
without blocking all the
other threads in the system, you must compile the program with
-threaded
.
getProcessExitCode :: ProcessHandle -> IO (Maybe ExitCode)Source
This is a non-blocking version of waitForProcess
. If the process is
still running, Nothing
is returned. If the process has exited, then
is returned where Just
ee
is the exit code of the process.
terminateProcess :: ProcessHandle -> IO ()Source
Attempts to terminate the specified process. This function should
not be used under normal circumstances - no guarantees are given regarding
how cleanly the process is terminated. To check whether the process
has indeed terminated, use getProcessExitCode
.
On Unix systems, terminateProcess
sends the process the SIGTERM signal.
On Windows systems, the Win32 TerminateProcess
function is called, passing
an exit code of 1.
Note: on Windows, if the process was a shell command created by
createProcess
with shell
, or created by runCommand
or
runInteractiveCommand
, then terminateProcess
will only
terminate the shell, not the command itself. On Unix systems, both
processes are in a process group and will be terminated together.
Arguments
:: ProcessHandle | Lead process in the process group |
-> IO () |
Sends an interrupt signal to the process group of the given process.
On Unix systems, it sends the group the SIGINT signal.
On Windows systems, it generates a CTRL_BREAK_EVENT and will only work for
processes created using createProcess
and setting the create_group
flag