Copyright | (c) The University of Glasgow 2004-2008 |
---|---|
License | BSD-style (see the file libraries/base/LICENSE) |
Maintainer | libraries@haskell.org |
Stability | experimental |
Portability | non-portable (requires concurrency) |
Safe Haskell | Safe |
Language | Haskell2010 |
System.Process
Contents
Description
Operations for creating and interacting with sub-processes.
- createProcess :: CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle)
- createProcess_ :: String -> CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle)
- shell :: String -> CreateProcess
- proc :: FilePath -> [String] -> CreateProcess
- data CreateProcess = CreateProcess {}
- data CmdSpec
- data StdStream
- data ProcessHandle
- callProcess :: FilePath -> [String] -> IO ()
- callCommand :: String -> IO ()
- spawnProcess :: FilePath -> [String] -> IO ProcessHandle
- spawnCommand :: String -> IO ProcessHandle
- readProcess :: FilePath -> [String] -> String -> IO String
- readProcessWithExitCode :: FilePath -> [String] -> String -> IO (ExitCode, String, String)
- showCommandForUser :: FilePath -> [String] -> String
- waitForProcess :: ProcessHandle -> IO ExitCode
- getProcessExitCode :: ProcessHandle -> IO (Maybe ExitCode)
- terminateProcess :: ProcessHandle -> IO ()
- interruptProcessGroupOf :: ProcessHandle -> IO ()
- createPipe :: IO (Handle, Handle)
- runProcess :: FilePath -> [String] -> Maybe FilePath -> Maybe [(String, String)] -> Maybe Handle -> Maybe Handle -> Maybe Handle -> IO ProcessHandle
- runCommand :: String -> IO ProcessHandle
- runInteractiveProcess :: FilePath -> [String] -> Maybe FilePath -> Maybe [(String, String)] -> IO (Handle, Handle, Handle, ProcessHandle)
- runInteractiveCommand :: String -> IO (Handle, Handle, Handle, ProcessHandle)
- system :: String -> IO ExitCode
- rawSystem :: String -> [String] -> IO ExitCode
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, ph)
,
where
- if
, thenstd_in
==CreatePipe
mb_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 }
Note that Handle
s provided for std_in
, std_out
, or std_err
via the
UseHandle
constructor will be closed by calling this function. This is not
always the desired behavior. In cases where you would like to leave the
Handle
open after spawning the child process, please use createProcess_
instead.
Arguments
:: String | function name (for error messages) |
-> CreateProcess | |
-> IO (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) |
This function is almost identical to
createProcess
. The only differences are:
Handle
s provided viaUseHandle
are not closed automatically.- This function takes an extra
String
argument to be used in creating error messages.
This function has been available from the System.Process.Internals module for some time, and is part of the System.Process module since version 1.2.1.0.
Since: 1.2.1.0
shell :: String -> CreateProcess Source
Construct a CreateProcess
record for passing to createProcess
,
representing a command to be passed to the shell.
proc :: FilePath -> [String] -> CreateProcess Source
Construct a CreateProcess
record for passing to createProcess
,
representing a raw command with arguments.
See RawCommand
for precise semantics of the specified FilePath
.
data CreateProcess Source
Constructors
CreateProcess | |
Fields
|
Constructors
ShellCommand String | A command line to execute using the shell |
RawCommand FilePath [String] | The name of an executable with a list of arguments The
|
Instances
IsString CmdSpec | construct a Since: 1.2.1.0 |
Constructors
Inherit | Inherit Handle from parent |
UseHandle Handle | Use the supplied Handle |
CreatePipe | Create a new pipe. The returned
|
data ProcessHandle Source
Simpler functions for common tasks
callProcess :: FilePath -> [String] -> IO () Source
Creates a new process to run the specified command with the given arguments, and wait for it to finish. If the command returns a non-zero exit code, an exception is raised.
If an asynchronous exception is thrown to the thread executing
callProcess
. The forked process will be terminated and
callProcess
will wait (block) until the process has been
terminated.
Since: 1.2.0.0
callCommand :: String -> IO () Source
Creates a new process to run the specified shell command. If the command returns a non-zero exit code, an exception is raised.
If an asynchronous exception is thrown to the thread executing
callCommand
. The forked process will be terminated and
callCommand
will wait (block) until the process has been
terminated.
Since: 1.2.0.0
spawnProcess :: FilePath -> [String] -> IO ProcessHandle Source
Creates a new process to run the specified raw command with the given
arguments. It does not wait for the program to finish, but returns the
ProcessHandle
.
Since: 1.2.0.0
spawnCommand :: String -> IO ProcessHandle Source
Creates a new process to run the specified shell command.
It does not wait for the program to finish, but returns the ProcessHandle
.
Since: 1.2.0.0
Arguments
:: FilePath | Filename of the executable (see |
-> [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. The external process inherits the standard error.
If an asynchronous exception is thrown to the thread executing
readProcess
, the forked process will be terminated and readProcess
will
wait (block) until the process has been terminated.
Output is returned strictly, so this is not suitable for interactive applications.
This function throws an IOError
if the process ExitCode
is
anything other than ExitSuccess
. If instead you want to get the
ExitCode
then use readProcessWithExitCode
.
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 or relative path
- A list of separate command line arguments to the program
- A string to pass on standard input to the forked process.
readProcessWithExitCode Source
Arguments
:: FilePath | Filename of the executable (see |
-> [String] | any arguments |
-> String | standard input |
-> IO (ExitCode, String, String) | exitcode, stdout, stderr |
readProcessWithExitCode
is like readProcess
but with two differences:
- it returns the
ExitCode
of the process, and does not throw any exception if the code is notExitSuccess
. - it reads and returns the output from process' standard error handle, rather than the process inheriting the standard error handle.
On Unix systems, see waitForProcess
for the meaning of exit codes
when the process died as the result of a signal.
Related utilities
showCommandForUser :: FilePath -> [String] -> String Source
Given a program p
and arguments args
,
showCommandForUser p args
returns a string suitable for pasting
into /bin/sh
(on Unix systems) or CMD.EXE
(on Windows).
Control-C handling on Unix
When running an interactive console process (such as a shell, console-based
text editor or ghci), we typically want that process to be allowed to handle
Ctl-C keyboard interrupts how it sees fit. For example, while most programs
simply quit on a Ctl-C, some handle it specially. To allow this to happen,
use the
option in the delegate_ctlc
= TrueCreateProcess
options.
The gory details:
By default Ctl-C will generate a SIGINT
signal, causing a UserInterrupt
exception to be sent to the main Haskell thread of your program, which if
not specially handled will terminate the program. Normally, this is exactly
what is wanted: an orderly shutdown of the program in response to Ctl-C.
Of course when running another interactive program in the console then we
want to let that program handle Ctl-C. Under Unix however, Ctl-C sends
SIGINT
to every process using the console. The standard solution is that
while running an interactive program, ignore SIGINT
in the parent, and let
it be handled in the child process. If that process then terminates due to
the SIGINT
signal, then at that point treat it as if we had recieved the
SIGINT
ourselves and begin an orderly shutdown.
This behaviour is implemented by createProcess
(and
waitForProcess
/ getProcessExitCode
) when the
option is set. In particular, the delegate_ctlc
= TrueSIGINT
signal will be ignored until
waitForProcess
returns (or getProcessExitCode
returns a non-Nothing
result), so it becomes especially important to use waitForProcess
for every
processes created.
In addition, in delegate_ctlc
mode, waitForProcess
and
getProcessExitCode
will throw a UserInterrupt
exception if the process
terminated with
. Typically you will not want to
catch this exception, but let it propagate, giving a normal orderly shutdown.
One detail to be aware of is that the ExitFailure
(-SIGINT)UserInterrupt
exception is thrown
synchronously in the thread that calls waitForProcess
, whereas normally
SIGINT
causes the exception to be thrown asynchronously to the main
thread.
For even more detail on this topic, see "Proper handling of SIGINT/SIGQUIT".
Process completion
waitForProcess :: ProcessHandle -> IO ExitCode Source
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
.
(Since: 1.2.0.0) On Unix systems, a negative value
indicates that the child was terminated by signal ExitFailure
-signumsignum
.
The signal numbers are platform-specific, so to test for a specific signal use
the constants provided by System.Posix.Signals in the unix
package.
Note: core dumps are not reported, use System.Posix.Process if you need this
detail.
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.
On Unix systems, see waitForProcess
for the meaning of exit codes
when the process died as the result of a signal.
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.
interruptProcessGroupOf Source
Arguments
:: ProcessHandle | A 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
createPipe :: IO (Handle, Handle) Source
Create a pipe for interprocess communication and return a
(readEnd, writeEnd)
Handle
pair.
Since: 1.2.1.0
Old deprecated functions
These functions pre-date createProcess
which is much more
flexible.
Arguments
:: FilePath | Filename of the executable (see |
-> [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
.
runCommand :: String -> IO ProcessHandle Source
Runs a command using the shell.
Arguments
:: FilePath | Filename of the executable (see |
-> [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
.
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
.
system :: String -> IO ExitCode Source
Computation system cmd
returns the exit code produced when the
operating system runs the shell command cmd
.
This computation may fail with one of the following
IOErrorType
exceptions:
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.
On Unix systems, see waitForProcess
for the meaning of exit codes
when the process died as the result of a signal.
rawSystem :: String -> [String] -> IO ExitCode Source
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
.