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Article contents:[[tags: manual]] [[toc:]] == Module (chicken process) This module offers procedures for interacting with subprocesses. * New in CHICKEN 5.4.0: Errors caused by underlying C calls that change errno will produce a condition object with an {{errno}} property, which can be accessed with {{(get-condition-property <the-condition-object> 'exn 'errno)}}. === Processes ==== process-execute <procedure>(process-execute PATHNAME [ARGUMENT-LIST [ENVIRONMENT-ALIST]])</procedure> Replaces the running process with a new process image from the program stored at {{PATHNAME}}, using the C library function {{execvp(3)}}. If the optional argument {{ARGUMENT-LIST}} is given, then it should contain a list of strings which are passed as arguments to the subprocess. If the optional argument {{ENVIRONMENT-ALIST}} is supplied, then the library function {{execve(2)}} is used, and the environment passed in {{ENVIRONMENT-ALIST}} (which should be of the form {{(("<NAME>" . "<VALUE>") ...)}}) is given to the invoked process. Note that {{execvp(3)}} respects the current setting of the {{PATH}} environment variable while {{execve(3)}} does not. This procedure never returns; it either replaces the process with a new one or it raises an exception in case something went wrong executing the program. On Windows, these procedures all have an additional optional parameter {{EXACT-FLAG}}, which defaults to {{#f}}. When {{#f}} is passed, any argument string with embedded whitespace will be wrapped in quotes. When {{#t}} no such wrapping occurs. ==== process-fork <procedure>(process-fork [THUNK [KILLOTHERS?]])</procedure> Creates a new child process with the UNIX system call {{fork()}}. Returns either the PID of the child process or 0. If {{THUNK}} is given, then the child process calls it as a procedure with no arguments and terminates. If {{THUNK}} is given and the optional argument {{KILLOTHERS?}} is true, then kill all other existing threads in the child process, leaving only the current thread to run {{THUNK}} and terminate. '''NOTE''': On native Windows builds (all except cygwin), this procedure is unimplemented and will raise an error. ==== process-run <procedure>(process-run COMMANDLINE)</procedure><br> <procedure>(process-run COMMAND ARGUMENT-LIST)</procedure> Creates a new child process. The PID of the new process is returned. * The single parameter version passes the {{COMMANDLINE}} to the system shell, so usual argument expansion can take place. Be careful to properly quote arguments with the {{qs}} procedure to avoid shell injection vulnerabilities. * The multiple parameter version directly invokes the {{COMMAND}} with the {{ARGUMENT-LIST}}, and is vastly preferred over the single-parameter version because of its better safety. ==== process-signal <procedure>(process-signal PID [SIGNAL])</procedure> Sends {{SIGNAL}} to the process with the id {{PID}} using the UNIX system call {{kill()}}. {{SIGNAL}} defaults to the value of the variable {{signal/term}}. '''NOTE''': On native Windows builds (all except cygwin), this procedure is unimplemented and will raise an error. ==== process-spawn <procedure>(process-spawn MODE COMMAND [ARGUMENT-LIST [ENVIRONMENT-LIST [EXACT-FLAG]]])</procedure> Creates and runs a new process with the given {{COMMAND}} filename and the optional {{ARGUMENT-LIST}} and {{ENVIRONMENT-LIST}}. {{MODE}} specifies how exactly the process should be executed and must be one or more of the {{spawn/...}} flags listed below. The {{EXACT-FLAG}}, default {{#f}}, controls quote-wrapping of argument strings. When {{#t}} quote-wrapping is not performed. Returns: * the exit status when synchronous * the PID when asynchronous * -1 when failure '''NOTE''': On all Unix-like builds (all except native MingW-based Windows platforms), this procedure is unimplemented and will raise an error. <constant>spawn/overlay</constant> <constant>spawn/wait</constant> <constant>spawn/nowait</constant> <constant>spawn/nowaito</constant> <constant>spawn/detach</constant> These variables contains special flags that specify the exact semantics of {{process-spawn}}: * {{spawn/overlay}} replaces the current process with the new one. * {{spawn/wait}} suspends execution of the current process until the spawned process returns. * {{spawn/nowait}} does the opposite ({{spawn/nowaito}} is identical, according to the Microsoft documentation) and runs the process asynchronously. * {{spawn/detach}} runs the new process in the background, without being attached to a console. ==== process-wait <procedure>(process-wait [PID [NOHANG]])</procedure> Suspends the current process until the child process with the id {{PID}} has terminated using the UNIX system call {{waitpid()}}. If {{PID}} is not given, then this procedure waits for any child process. If {{NOHANG}} is given and not {{#f}} then the current process is not suspended. This procedure returns three values: * {{PID}} or 0, if {{NOHANG}} is true and the child process has not terminated yet. * {{#t}} if the process exited normally or {{#f}} otherwise. * either the exit status, if the process terminated normally or the signal number that terminated/stopped the process. Note that suspending the current process implies that all threads are suspended as well. On Windows, {{process-wait}} always returns {{#t}} for a terminated process and only the exit status is available. (Windows does not provide signals as an interprocess communication method.) ==== process-sleep <procedure>(process-sleep SECONDS)</procedure> Puts the process to sleep for {{SECONDS}}. Returns either 0 if the time has completely elapsed, or the number of remaining seconds, if a signal occurred. ==== process <procedure>(process COMMANDLINE)</procedure><br> <procedure>(process COMMAND ARGUMENT-LIST [ENVIRONMENT-ALIST ENCODING])</procedure> Creates a subprocess and returns three values: an input port from which data written by the sub-process can be read, an output port from which any data written to will be received as input in the sub-process and the process-id of the started sub-process. Blocking reads and writes to or from the ports returned by {{process}} only block the current thread, not other threads executing concurrently. Standard error for the subprocess is linked up to the current process's standard error (see {{process*}} if you want to reify its standard error into a separate port). * The single parameter version passes the string {{COMMANDLINE}} to the host-system's shell that is invoked as a subprocess. * The multiple parameter version directly invokes the {{COMMAND}} as a subprocess. The {{ARGUMENT-LIST}} is directly passed, as is {{ENVIRONMENT-ALIST}}. These arguments have the same form as the ones of {{process-execute}}. {{ENCODING}} should be a symbol specifying the encoding to be used for I/O operations, the default is {{utf-8}}. The encodings for the returned in and output ports can be subsequently changed by using the {{port-encoding}} setter. Not using the shell may be preferrable for security reasons. Once both the input- and output ports are closed, an implicit {{waitpid(3)}} is done to wait for the subprocess to finish or to reap a subprocess that has terminated. If the subprocess has not finished, waiting for it will necessarily block all executing threads. ==== process* <procedure>(process* COMMANDLINE)</procedure><br> <procedure>(process* COMMAND ARGUMENT-LIST [ENVIRONMENT-ALIST ENCODING])</procedure> Like {{process}} but returns 4 values: an input port from which data written by the sub-process can be read, an output port from which any data written to will be received as input in the sub-process, the process-id of the started sub-process, and an input port from which data written by the sub-process to {{stderr}} can be read. === Shell commands The commands below are all string-based. This means you have to be very careful to properly quote any arguments to subprocesses, to avoid shell injection bugs which can lead to arbitrary code execution. You can quote arguments with the {{qs}} procedure, but it is strongly recommended you use {{fork}} with {{process-execute}} or the multi-argument versions of the {{process}}, {{process*}} or {{process-run}} procedures. ==== qs <procedure>(qs STRING [PLATFORM])</procedure> Escapes {{STRING}} suitably for passing to a shell command on {{PLATFORM}}. {{PLATFORM}} defaults to the value of {{(build-platform)}} and indicates in which style the argument should be quoted. On Windows systems, the string is simply enclosed in double-quote ({{"}}) characters, on UNIXish systems, characters that would have a special meaning to the shell are escaped using backslash ({{\}}). ==== system <procedure>(system STRING)</procedure> Execute shell command. The functionality offered by this procedure depends on the capabilities of the host shell. If the forking of a subprocess failed, an exception is raised. Otherwise the return status of the subprocess is returned unaltered. On a UNIX system, that value is the raw return value of waitpid(2), which contains signal, core dump and exit status. It is 0 on success. To pull out the signal number or exit status portably requires POSIX calls, but in a pinch you can use something like this: <enscript highlight='scheme'> ;; Returns two values: #t if the process exited normally or #f otherwise; ;; and either the exit status, or the signal number if terminated via signal. (define (process-status rc) (define (wait-signaled? x) (not (= 0 (bitwise-and x 127)))) (define (wait-signal x) (bitwise-and x 127)) (define (wait-exit-status x) (arithmetic-shift x -8)) (if (wait-signaled? rc) (values #f (wait-signal rc)) (values #t (wait-exit-status rc)))) #;> (process-status (system "exit 42")) #t 42 </enscript> ==== system* <procedure>(system* STRING)</procedure> Similar to {{(system STRING)}}, but signals an error should the invoked program return a nonzero exit status. === Pipes ==== call-with-input-pipe ==== call-with-output-pipe <procedure>(call-with-input-pipe CMDLINE PROC [MODE])</procedure><br> <procedure>(call-with-output-pipe CMDLINE PROC [MODE])</procedure> Call {{PROC}} with a single argument: a input- or output port for a pipe connected to the subprocess named in {{CMDLINE}}. If {{PROC}} returns normally, the pipe is closed and any result values are returned. ==== close-input-pipe ==== close-output-pipe <procedure>(close-input-pipe PORT)</procedure><br> <procedure>(close-output-pipe PORT)</procedure> Closes the pipe given in {{PORT}} and waits until the connected subprocess finishes. The exit-status code of the invoked process is returned. ==== create-pipe <procedure>(create-pipe)</procedure> The fundamental pipe-creation operator. Calls the C function {{pipe()}} and returns 2 values: the file-descriptors of the input- and output-ends of the pipe. On Windows, there is an optional parameter {{MODE}}, which defaults to {{open/binary | open/noinherit}}. This can be {{open/binary}} or {{open/text}}, optionally or'ed with {{open/noinherit}}. ==== open-input-pipe <procedure>(open-input-pipe CMDLINE [MODE])</procedure> Spawns a subprocess with the command-line string {{CMDLINE}} and returns a port, from which the output of the process can be read. If {{MODE}} is specified, it should be the keyword {{#:text}} (the default) or {{#:binary}}. ==== open-output-pipe <procedure>(open-output-pipe CMDLINE [MODE])</procedure> Spawns a subprocess with the command-line string {{CMDLINE}} and returns a port. Anything written to that port is treated as the input for the process. If {{MODE}} is specified, it should be the keyword {{#:text}} (the default) or {{#:binary}}. ==== pipe/buf <constant>pipe/buf</constant> This variable contains the maximal number of bytes that can be written atomically into a pipe or FIFO. ==== with-input-from-pipe ==== with-output-to-pipe <procedure>(with-input-from-pipe CMDLINE THUNK [MODE])</procedure><br> <procedure>(with-output-to-pipe CMDLINE THUNK [MODE])</procedure> Temporarily set the value of {{current-input-port/current-output-port}} to a port for a pipe connected to the subprocess named in {{CMDLINE}} and call the procedure {{THUNK}} with no arguments. After {{THUNK}} returns normally the pipe is closed and the standard input-/output port is restored to its previous value and any result values are returned. <enscript highlight=scheme> (with-output-to-pipe "gs -dNOPAUSE -sDEVICE=jpeg -dBATCH -sOutputFile=signballs.jpg -g600x600 -q -" (lambda () (print #<<EOF %!IOPSC-1993 %%Creator: HAYAKAWA Takashi<xxxxxxxx@xx.xxxxxx.xx.xx> /C/neg/d/mul/R/rlineto/E/exp/H{{cvx def}repeat}def/T/dup/g/gt/r/roll/J/ifelse 8 H/A/copy(z&v4QX&93r9AxYQOZomQalxS2w!!O&vMYa43d6r93rMYvx2dca!D&cjSnjSnjjS3o!v&6A X&55SAxM1CD7AjYxTTd62rmxCnTdSST0g&12wECST!&!J0g&D1!&xM0!J0g!l&544dC2Ac96ra!m&3A F&&vGoGSnCT0g&wDmlvGoS8wpn6wpS2wTCpS1Sd7ov7Uk7o4Qkdw!&Mvlx1S7oZES3w!J!J!Q&7185d Z&lx1CS9d9nE4!k&X&MY7!&1!J!x&jdnjdS3odS!N&mmx1C2wEc!G&150Nx4!n&2o!j&43r!U&0777d ]&2AY2A776ddT4oS3oSnMVC00VV0RRR45E42063rNz&v7UX&UOzF!F!J![&44ETCnVn!a&1CDN!Y&0M V1c&j2AYdjmMdjjd!o&1r!M){( )T 0 4 3 r put T(/)g{T(9)g{cvn}{cvi}J}{($)g[]J}J cvx}forall/moveto/p/floor/w/div/S/add 29 H[{[{]setgray fill}for Y}for showpage EOF ) ) ) </enscript> === Windows specific notes Use of UTF8 encoded strings for pathnames is not supported. Windows uses a 16-bit UNICODE encoding with special system calls for wide-character support. Only single-byte string encoding can be used. --- Previous: [[Module (chicken pretty-print)]] Next: [[Module (chicken process signal)]] Description of your changes:

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