See also
- shell/2
- 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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Predicate process_create/3 |
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:
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.
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.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.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=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.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.
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).
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.environment(List)
is handled as env(List)
,
i.e., the environment is not inherited.