36.5 Controlling Subprocesses

Octave includes some high-level commands like system and popen for starting subprocesses. If you want to run another program to perform some task and then look at its output, you will probably want to use these functions.

Octave also provides several very low-level Unix-like functions which can also be used for starting subprocesses, but you should probably only use them if you can’t find any way to do what you need with the higher-level functions.

system ("문자열")

system ("문자열", return_output)

system ("문자열", return_output, type)

[상태, output] = system (…)

Execute a shell command specified by 문자열.

If the optional argument type is "async", the process is started in the background and the process ID of the child process is returned immediately. Otherwise, the child process is started and Octave waits until it exits. If the type argument is omitted, it defaults to the value "sync".

If system is called with one or more output arguments, or if the optional argument return_output is true and the subprocess is started synchronously, then the output from the command is returned as a variable. Otherwise, if the subprocess is executed synchronously, its output is sent to the standard output. To send the output of a command executed with system through the pager, use a command like

[~, text] = system ("cmd");
more on;
disp (text);

or

more on;
printf ("%s\n", nthargout (2, "system", "cmd"));

The system function can return two values. The first is the exit status of the command and the second is any output from the command that was written to the standard output stream. For example,

[status, output] = system ("echo foo & exit 2");

will set the variable output to the string ‘foo’, and the variable 상태 to the integer ‘2’.

For commands run asynchronously, 상태 is the process id of the command shell that is started to run the command.

The shell used for executing commands varies with operating system and is typically /bin/sh for UNIX systems and cmd.exe for Windows systems.

같이 보기: unix, dos.

unix ("command")

상태 = unix ("command")

[상태, text] = unix ("command")

[…] = unix ("command", "-echo")

Execute a system command if running under a Unix-like operating system, otherwise do nothing.

Octave waits for the external command to finish before returning the exit status of the program in 상태 and any output in text.

When called with no output argument, or the "-echo" argument is given, then text is also sent to standard output.

같이 보기: dos, system, isunix, ismac, ispc.

dos ("command")

상태 = dos ("command")

[상태, text] = dos ("command")

[…] = dos ("command", "-echo")

Execute a system command if running under a Windows-like operating system, otherwise do nothing.

Octave waits for the external command to finish before returning the exit status of the program in 상태 and any output in text.

When called with no output argument, or the "-echo" argument is given, then text is also sent to standard output.

같이 보기: unix, system, isunix, ismac, ispc.

open 기록철

output = open (기록철)

Open the file 기록철 in Octave or in an external application based on the file type as determined by the filename extension.

By default, recognized file types are

.m

Open file in the editor. No output value is returned.

.mat

octave-workspace

Open the data file with load. If no return value output is requested, variables are loaded in the base workspace. Otherwise output will be a structure containing loaded data. See load function.

.ofig

Open the figure with hgload. See hgload function.

.fig, .ofig

Load the figure

.exe

Execute the program (on Windows systems only). No output value is returned.

Custom file extensions may also be handled if a function openxxx, where xxx is the extension, is found in the load path. The function must accept the file name as input. For example, in order to load ".dat" data files in the base workspace, as is done by default for ".mat" files, one may define "opendat.m" with the following contents:

function retval = opendat (fname)
  evalin ("base", sprintf ("load ('%s');", fname));
endfunction

Other file types are opened in the appropriate external application.

output = perl (scriptfile)

output = perl (scriptfile, argument1, argument2, …)

[output, 상태] = perl (…)

Invoke Perl script scriptfile, possibly with a list of command line arguments.

Return output in output and optional status in 상태. If scriptfile is not an absolute filename it is searched for in the current directory and then in the Octave loadpath.

같이 보기: system, python.

output = python (scriptfile)

output = python (scriptfile, argument1, argument2, …)

[output, 상태] = python (…)

Invoke Python script scriptfile, possibly with a list of command line arguments.

Return output in output and optional status in 상태. If scriptfile is not an absolute filename it is searched for in the current directory and then in the Octave loadpath.

같이 보기: system, perl.

기록철_식별자 = popen (command, 방식)

Start a process and create a pipe.

The name of the command to run is given by command. The argument 방식 may be

"r"

The pipe will be connected to the standard output of the process, and open for reading.

"w"

The pipe will be connected to the standard input of the process, and open for writing.

The file identifier corresponding to the input or output stream of the process is returned in 기록철_식별자.

For example:

fid = popen ("ls -ltr / | tail -3", "r");
while (ischar (s = fgets (fid)))
  fputs (stdout, s);
endwhile

   -| drwxr-xr-x  33 root  root  3072 Feb 15 13:28 etc
   -| drwxr-xr-x   3 root  root  1024 Feb 15 13:28 lib
   -| drwxrwxrwt  15 root  root  2048 Feb 17 14:53 tmp

같이 보기: popen2.

pclose (기록철_식별자)

Close a file identifier that was opened by popen.

The function fclose may also be used for the same purpose.

같이 보기: fclose, popen.

[in, out, pid] = popen2 (command, args)

Start a subprocess with two-way communication.

The name of the process is given by command, and args is an array or cell array of strings containing options for the command.

The file identifiers for the input and output streams of the subprocess are returned in in and out. If execution of the command is successful, pid contains the process ID of the subprocess. Otherwise, pid is -1.

For example:

[in, out, pid] = popen2 ("sort", "-r");
fputs (in, "these\nare\nsome\nstrings\n");
fclose (in);
EAGAIN = errno ("EAGAIN");
done = false;
do
  s = fgets (out);
  if (ischar (s))
    fputs (stdout, s);
  elseif (errno () == EAGAIN)
    pause (0.1);
    fclear (out);
  else
    done = true;
  endif
until (done)
fclose (out);
waitpid (pid);

   -| these
   -| strings
   -| some
   -| are

Note that popen2, unlike popen, will not "reap" the child process. If you don’t use waitpid to check the child’s exit status, it will linger until Octave exits.

같이 보기: popen, waitpid.

값 = EXEC_PATH ()

옛_값 = EXEC_PATH (새_값)

EXEC_PATH (새_값, "local")

Query or set the internal variable that specifies a colon separated list of directories to append to the shell PATH when executing external programs.

The initial value of is taken from the environment variable OCTAVE_EXEC_PATH, but that value can be overridden by the command line argument --exec-path PATH.

함수 안에서 "local" 선택지를 넣어 부르면, 함수와 함수가 부른 종속 절차의 변수가 지역적으로 바뀝니다. 함수가 종료되면 원래 변숫값이 되돌아옵니다.

같이 보기: IMAGE_PATH, OCTAVE_HOME, OCTAVE_EXEC_HOME.

In most cases, the following functions simply decode their arguments and make the corresponding Unix system calls. For a complete example of how they can be used, look at the definition of the function popen2.

[pid, 안내] = fork ()

Create a copy of the current process.

Fork can return one of the following values:

> 0

You are in the parent process. The value returned from fork is the process id of the child process. You should probably arrange to wait for any child processes to exit.

0

You are in the child process. You can call exec to start another process. If that fails, you should probably call exit.

< 0

The call to fork failed for some reason. You must take evasive action. A system dependent error message will be waiting in 안내.

[오류, 안내] = exec (기록철, args)

Replace current process with a new process.

Calling exec without first calling fork will terminate your current Octave process and replace it with the program named by 기록철. For example,

exec ("ls", "-l")

will run ls and return you to your shell prompt.

If successful, exec does not return. If exec does return, 오류 will be nonzero, and 안내 will contain a system-dependent error message.

[read_fd, write_fd, 오류, 안내] = pipe ()

Create a pipe and return the reading and writing ends of the pipe into read_fd and write_fd respectively.

If successful, 오류 is 0 and 안내 is an empty string. Otherwise, 오류 is nonzero and 안내 contains a system-dependent error message.

같이 보기: mkfifo.

[기록철_식별자, 안내] = dup2 (old, new)

Duplicate a file descriptor.

If successful, 기록철_식별자 is greater than zero and contains the new file ID. Otherwise, 기록철_식별자 is negative and 안내 contains a system-dependent error message.

같이 보기: fopen, fclose, fcntl.

[pid, 상태, 안내] = waitpid (pid, options)

Wait for process pid to terminate.

The pid argument can be:

-1

Wait for any child process.

0

Wait for any child process whose process group ID is equal to that of the Octave interpreter process.

> 0

Wait for termination of the child process with ID pid.

The options argument can be a bitwise OR of zero or more of the following constants:

0

Wait until signal is received or a child process exits (this is the default if the options argument is missing).

WNOHANG

Do not hang if status is not immediately available.

WUNTRACED

Report the status of any child processes that are stopped, and whose status has not yet been reported since they stopped.

WCONTINUE

Return if a stopped child has been resumed by delivery of SIGCONT. This value may not be meaningful on all systems.

If the returned value of pid is greater than 0, it is the process ID of the child process that exited. If an error occurs, pid will be less than zero and 안내 will contain a system-dependent error message. The value of 상태 contains additional system-dependent information about the subprocess that exited.

같이 보기: WCONTINUE, WCOREDUMP, WEXITSTATUS, WIFCONTINUED, WIFSIGNALED, WIFSTOPPED, WNOHANG, WSTOPSIG, WTERMSIG, WUNTRACED.

WCONTINUE ()

Return the numerical value of the WCONTINUE macro.

WCONTINUE is the option argument that may be passed to waitpid to indicate that it should also return if a stopped child has been resumed by delivery of a SIGCONT signal.

같이 보기: waitpid, WNOHANG, WUNTRACED.

WCOREDUMP (상태)

Given 상태 from a call to waitpid, return true if the child produced a core dump.

This function should only be employed if WIFSIGNALED returned true. The macro used to implement this function is not specified in POSIX.1-2001 and is not available on some Unix implementations (e.g., AIX, SunOS).

같이 보기: waitpid, WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WIFSTOPPED, WSTOPSIG, WIFCONTINUED.

WEXITSTATUS (상태)

Given 상태 from a call to waitpid, return the exit status of the child.

This function should only be employed if WIFEXITED returned true.

같이 보기: waitpid, WIFEXITED, WIFSIGNALED, WTERMSIG, WCOREDUMP, WIFSTOPPED, WSTOPSIG, WIFCONTINUED.

WIFCONTINUED (상태)

Given 상태 from a call to waitpid, return true if the child process was resumed by delivery of SIGCONT.

같이 보기: waitpid, WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WCOREDUMP, WIFSTOPPED, WSTOPSIG.

WIFSIGNALED (상태)

Given 상태 from a call to waitpid, return true if the child process was terminated by a signal.

같이 보기: waitpid, WIFEXITED, WEXITSTATUS, WTERMSIG, WCOREDUMP, WIFSTOPPED, WSTOPSIG, WIFCONTINUED.

WIFSTOPPED (상태)

Given 상태 from a call to waitpid, return true if the child process was stopped by delivery of a signal.

This is only possible if the call was done using WUNTRACED or when the child is being traced (see ptrace(2)).

같이 보기: waitpid, WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WCOREDUMP, WSTOPSIG, WIFCONTINUED.

WIFEXITED (상태)

Given 상태 from a call to waitpid, return true if the child terminated normally.

같이 보기: waitpid, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WCOREDUMP, WIFSTOPPED, WSTOPSIG, WIFCONTINUED.

WNOHANG ()

Return the numerical value of the WNOHANG macro.

WNOHANG is the option argument that may be passed to waitpid to indicate that it should return its status immediately instead of waiting for a process to exit.

같이 보기: waitpid, WUNTRACED, WCONTINUE.

WSTOPSIG (상태)

Given 상태 from a call to waitpid, return the number of the signal which caused the child to stop.

This function should only be employed if WIFSTOPPED returned true.

같이 보기: waitpid, WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WCOREDUMP, WIFSTOPPED, WIFCONTINUED.

WTERMSIG (상태)

Given 상태 from a call to waitpid, return the number of the signal that caused the child process to terminate.

This function should only be employed if WIFSIGNALED returned true.

같이 보기: waitpid, WIFEXITED, WEXITSTATUS, WIFSIGNALED, WCOREDUMP, WIFSTOPPED, WSTOPSIG, WIFCONTINUED.

WUNTRACED ()

Return the numerical value of the WUNTRACED macro.

WUNTRACED is the option argument that may be passed to waitpid to indicate that it should also return if the child process has stopped but is not traced via the ptrace system call

같이 보기: waitpid, WNOHANG, WCONTINUE.

[오류, 안내] = fcntl (기록철_식별자, request, 매개 변수)

Change the properties of the open file 기록철_식별자.

The following values may be passed as request:

F_DUPFD

Return a duplicate file descriptor.

F_GETFD

Return the file descriptor flags for 기록철_식별자.

F_SETFD

Set the file descriptor flags for 기록철_식별자.

F_GETFL

Return the file status flags for 기록철_식별자. The following codes may be returned (some of the flags may be undefined on some systems).

O_RDONLY

Open for reading only.

O_WRONLY

Open for writing only.

O_RDWR

Open for reading and writing.

O_APPEND

Append on each write.

O_CREAT

Create the file if it does not exist.

O_NONBLOCK

Non-blocking mode.

O_SYNC

Wait for writes to complete.

O_ASYNC

Asynchronous I/O.

F_SETFL

Set the file status flags for 기록철_식별자 to the value specified by 매개 변수. The only flags that can be changed are O_APPEND and O_NONBLOCK.

If successful, 오류 is 0 and 안내 is an empty string. Otherwise, 오류 is nonzero and 안내 contains a system-dependent error message.

같이 보기: fopen, dup2.

[오류, 안내] = kill (pid, sig)

Send signal sig to process pid.

If pid is positive, then signal sig is sent to pid.

If pid is 0, then signal sig is sent to every process in the process group of the current process.

If pid is -1, then signal sig is sent to every process except process 1.

If pid is less than -1, then signal sig is sent to every process in the process group -pid.

If sig is 0, then no signal is sent, but error checking is still performed.

Return 0 if successful, otherwise return -1.

SIG ()

Return a structure containing Unix signal names and their defined values.