- process_create∕3 (same page content as this page, i.e. process_create/3, but it's another page maybe with more comments)
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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 separate 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.
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, or by using the two-argument form of
pipe, which accepts an
encoding(Encoding)option. The options
stderrmay use the same stream, in which case both output streams are connected to the same Prolog stream.
user_input, etc. are bound to a file handle but not to 0,1,2 the process I/O is bound to the file handles of these streams.
encoding(+Encoding)are supported, which have the same meaning as the stream properties of the same name (see stream_property/2). StreamOptions is provided mainly for SICStus compatibility - the SWI-Prolog predicate set_stream/2 can be used for the same purpose.
file_no). This option is not provided by the SICStus implementation.
environment(List), but only the specified variables are passed, i.e., no variables are inherited.
Name=Valueterms, where Value is expanded the same way as the Args argument. If neither
environmentis passed the environment is inherited from the Prolog process. At most one
environment(List)term may appear in the options. If multiple appear a
permission_erroris raised for the second option.
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)
If the user specifies the
process(-PID) option, he must call
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.
environment(List)is handled as
env(List), i.e., the environment is not inherited.