:- use_module(library(process)).(can be autoloaded)
pathfile alias to specify an executable file on the current PATH. Args is a list of arguments that are handed to the new process. On Unix systems, each element in the list becomes a seperate argument in the new process. In Windows, the arguments are simply concatenated to form the commandline. Each argument itself is either a primitive or a list of primitives. A primitive is either atomic or a term
file(Spec), the system inserts a filename using the OS filename conventions which is properly quoted if needed.
- Bind the standard streams of the new process. Spec is one of
the terms below. If
pipe(Pipe)is used, the Prolog stream is a stream in text-mode using the encoding of the default locale. The encoding can be changed using set_stream/2. The options
stderrmay use the same stream, in which case both output streams are connected to the same Prolog stream.
- Just share with the Prolog I/O streams
- Bind to a null stream. Reading from such a stream returns end-of-file, writing produces no output
- Attach input and/or output to a Prolog stream.
- Run the new process in Directory. Directory can be a compound specification, which is converted using absolute_file_name/3.
- Specify the environment for the new process. List is a list of Name=Value terms. Note that the current implementation does not pass any environment variables. If unspecified, the environment is inherited from the Prolog process.
- Unify PID with the process id of the created process.
- In Unix: If
true, detach the process from the terminal Currently mapped to
setsid(); Also creates a new process group for the child In Windows: If
true, detach the process from the current job via the CREATE_BREAKAWAY_FROM_JOB flag. In Vista and beyond, processes launched from the shell directly have the 'compatibility assistant' attached to them automatically unless they have a UAC manifest embedded in them. This means that you will get a permission denied error if you try and assign the newly-created PID to a job you create yourself.
true, create a window for the process (Windows only)
- In Unix: specifies the process priority for the newly created process. Priority must be an integer between -20 and 19. Positive values are nicer to others, and negative values are less so. The default is zero. Users are free to lower their own priority. Only the super-user may raise it to less-than zero.
If the user specifies the
process(-PID) option, he must
process_wait/2 to reclaim the
process. Without this option, the system will wait for completion of the
process after the last pipe stream is closed.
If the process is not waited for, it must succeed with status 0. If not, an process_error is raised.
On Windows this call is an interface to the CreateProcess() API. The
commandline consists of the basename of Exe and the arguments
formed from Args. Arguments are separated by a single space.
If all characters satisfy
iswalnum() it is unquoted. If the
argument contains a double-quote it is quoted using single quotes. If
both single and double quotes appear a domain_error is raised, otherwise
double-quote are used.
The CreateProcess() API has many options. Currently only the
CREATE_NO_WINDOW options is supported through the
window(+Bool) option. If omitted, the default is to use
this option if the application has no console. Future versions are
likely to support more window specific options and replace
First, a very simple example that behaves the same as
shell('ls -l'), except for error handling:
?- process_create(path(ls), ['-l'], ).
The following example uses grep to find all matching lines in a file.
grep(File, Pattern, Lines) :- setup_call_cleanup( process_create(path(grep), [ Pattern, file(File) ], [ stdout(pipe(Out)) ]), read_lines(Out, Lines), close(Out)). read_lines(Out, Lines) :- read_line_to_codes(Out, Line1), read_lines(Line1, Out, Lines). read_lines(end_of_file, _, ) :- !. read_lines(Codes, Out, [Line|Lines]) :- atom_codes(Line, Codes), read_line_to_codes(Out, Line2), read_lines(Line2, Out, Lines).
process_error(Exe, Status)where Status is one of
killed(Signal). Raised if the process is waited for (i.e., Options does not include
process(-PID)), and does not exit with status 0.