Create a new process running the file Exe and using arguments
from the given list. Exe is a file specification as handed to
absolute_file_name/3. Typically one use
the path file 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). Using file(Spec), the
system inserts a filename using the OS filename conventions which is
properly quoted if needed.
Options:
- stdin(Spec)
- stdout(Spec)
- stderr(Spec)
- 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,
or by using the two-argument form of pipe, which accepts an
encoding(Encoding) option. The options stdout
and stderr may use the same stream, in which case both
output streams are connected to the same Prolog stream.
- std
- Just share with the Prolog I/O streams. On Unix, if the
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.
- null
- Bind to a null stream. Reading from such a stream returns
end-of-file, writing produces no output
- pipe(-Stream)
- pipe(-Stream, +StreamOptions)
- Attach input and/or output to a Prolog stream. The optional StreamOptions
argument is a list of options that affect the stream. Currently only the
options
type(+Type) and 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.
- stream(+Stream)
- Attach input or output to an existing Prolog stream. This stream must be
associated with an OS file handle (see stream_property/2,
property
file_no). This option is not provided by
the SICStus implementation.
- cwd(+Directory)
- Run the new process in Directory. Directory can be
a compound specification, which is converted using
absolute_file_name/3. See also process_set_method/1.
- env(+List)
- As
environment(List), but only the specified
variables are passed, i.e., no variables are inherited.
- environment(+List)
- Specify additional environment variables for the new process.
List is a list of
Name=Value terms, where Value
is expanded the same way as the Args argument. If neither env
nor
environment is passed the environment is inherited from the
Prolog process. At most one env(List) or environment(List)
term may appear in the options. If multiple appear a
permission_error is raised for the second option.
- process(-PID)
- Unify PID with the process id of the created process.
- detached(+Bool)
- 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.
- window(+Bool)
- If
true, create a window for the process (Windows only)
- priority(+Priority)
- 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
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.
Windows notes
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
win_exec/2.
Examples
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).
- Errors
process_error(Exe, Status) where Status is one of
exit(Code) or killed(Signal). Raised if the
process is waited for (i.e., Options does not include
process(-PID)), and does not exit with status 0.- bug
- On Windows,
environment(List) is handled as env(List),
i.e., the environment is not inherited.
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