# Protocol/1 (Used to capture screen to file) **URL:** \ **Category:** Wiki\ **Tags:** how-to\ **Created:** [May 20, 2019, 2:56pm UTC](https://swi-prolog.discourse.group/t/protocol-1-used-to-capture-screen-to-file/675 "2019-05-20T14:56:12Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![Wiki](https://avatars.discourse-cdn.com/v4/letter/w/e8c25b/32.png) [@Wiki](https://swi-prolog.discourse.group/u/Wiki)\ **Post date:** [May 20, 2019, 2:56pm UTC](https://swi-prolog.discourse.group/t/protocol-1-used-to-capture-screen-to-file/675/1 "2019-05-20T14:56:12Z")
How to - [protocol/1](http://www.swi-prolog.org/pldoc/man?predicate=protocol/1) > Note: Do not reply to this topic, questions, concerns, comments, etc. are to handled in > [Wiki discussion: How to - protocol/1](https://swi-prolog.discourse.group/t/wiki-discussion-how-to-protocol-1/676) > Note: This is a wiki and if you have [Trust level](https://blog.discourse.org/2018/06/understanding-discourse-trust-levels/): [Basic](https://swi-prolog.discourse.group/badges/1/basic) you can edit this by clicking on the pencil icon in the lower right. ![Capture](https://global.discourse-cdn.com/free1/uploads/swiprolog/original/1X/bfd4c3b77dc7f3f98ece3d5ae3202fcccb0fb8b3.png) > These topics also have history so they can be rolled-back if needed. [protocol/1](http://www.swi-prolog.org/pldoc/man?predicate=protocol/1) will copy the output that goes to the screen to a file. So if you run a [trace/0](http://www.swi-prolog.org/pldoc/man?predicate=trace/0) and the output goes to the screen, a copy will be sent to a file. To simplify having to write the entire path for protocol/1 I find it easier to set the current working directory using [working\_directory/2](http://www.swi-prolog.org/pldoc/man?predicate=working_directory/2) and then only set the specific file with protocol/1. ## Example For this example create a file, e.g. > trace\_example.pl and add some facts and predicates to demonstrate tracing. ``` parent(ann,helen). parent(helen,henry). parent(henry,mary). ancestor(X,Y) :- parent(X,Y). ancestor(X,Y) :- parent(X,Z), ancestor(Z,Y). ``` Open SWI-Prolog top level and use [consult/1](http://www.swi-prolog.org/pldoc/man?predicate=consult/1) to load the file ``` consult("C:/ ... /trace_example.pl"). ``` NB On Windows the directory separators are / not \. Change them if necessary. Since the SWI-Prolog terminal on Windows will default to using color with tracing and that will add unneeded escape sequences to the output file [set\_prolog\_flag/2](http://www.swi-prolog.org/pldoc/man?predicate=set_prolog_flag/2) needs to be run to turn the color off. ``` ?- set_prolog_flag(color_term,false). true. ``` Verify that the terminal is not using color. ``` ?- current_prolog_flag(color_term,X). X = false. ``` A quick run to verify the predicate and facts work ``` ?- ancestor(ann,henry). true ; false. ``` Now set the current working directory to where the output file will be created. ``` ?- working_directory(_,"C:/Users/Eric/Documents/Prolog"). ``` and verify that the change occurred ``` ?- working_directory(CWD,CWD). CWD = 'c:/users/eric/documents/prolog/'. ``` Since I don’t want to press the space bar for each trace output I disable user interaction for all the debug ports using [leash/1](http://www.swi-prolog.org/pldoc/man?predicate=leash/1) - **NOTE** : The space bar still needs to be pressed to get the next result. ([ref](https://swi-prolog.discourse.group/t/is-leash-all-broken/4585)) ``` ?- leash(-all). ``` and since I want to see all of the output from all of the debug ports I enable them all with [visible/1](http://www.swi-prolog.org/pldoc/doc_for?object=visible/1) ``` ?- visible(+all). ``` Enable the copying/capture of the screen to a file ``` ?- protocol("./trace_output.txt"). ``` start the tracer ``` ?- trace. ``` and run a query to be traced ``` ?- ancestor(ann,henry). Call: (8) ancestor(ann, henry) ? creep Call: (9) parent(ann, henry) ? creep Fail: (9) parent(ann, henry) ? creep Redo: (8) ancestor(ann, henry) ? creep Call: (9) parent(ann, _1124) ? creep Exit: (9) parent(ann, helen) ? creep Call: (9) ancestor(helen, henry) ? creep Call: (10) parent(helen, henry) ? creep Exit: (10) parent(helen, henry) ? creep Exit: (9) ancestor(helen, henry) ? creep Exit: (8) ancestor(ann, henry) ? creep true ; Redo: (9) ancestor(helen, henry) ? creep Call: (10) parent(helen, _1124) ? creep Exit: (10) parent(helen, henry) ? creep Call: (10) ancestor(henry, henry) ? creep Call: (11) parent(henry, henry) ? creep Fail: (11) parent(henry, henry) ? creep Redo: (10) ancestor(henry, henry) ? creep Call: (11) parent(henry, _1124) ? creep Exit: (11) parent(henry, mary) ? creep Call: (11) ancestor(mary, henry) ? creep Call: (12) parent(mary, henry) ? creep Fail: (12) parent(mary, henry) ? creep Redo: (11) ancestor(mary, henry) ? creep Call: (12) parent(mary, _1124) ? creep Fail: (12) parent(mary, _1124) ? creep Fail: (11) ancestor(mary, henry) ? creep Fail: (10) ancestor(henry, henry) ? creep Fail: (9) ancestor(helen, henry) ? creep Fail: (8) ancestor(ann, henry) ? creep false. ``` end the tracing ``` ?- nodebug. ``` and end the copying of the screen to the file ``` ?- noprotocol. ``` Now open the file `C:\Users\Eric\Documents\Prolog\trace_output.txt` ``` true. 10 ?- trace. true. [trace] 10 ?- ancestor(ann,henry). Call: (8) ancestor(ann, henry) Unify: (8) ancestor(ann, henry) Call: (9) parent(ann, henry) Fail: (9) parent(ann, henry) Redo: (8) ancestor(ann, henry) Unify: (8) ancestor(ann, henry) Call: (9) parent(ann, _6466) Unify: (9) parent(ann, helen) Exit: (9) parent(ann, helen) Call: (9) ancestor(helen, henry) Unify: (9) ancestor(helen, henry) Call: (10) parent(helen, henry) Unify: (10) parent(helen, henry) Exit: (10) parent(helen, henry) Exit: (9) ancestor(helen, henry) Exit: (8) ancestor(ann, henry) true ; Redo: (9) ancestor(helen, henry) Unify: (9) ancestor(helen, henry) Call: (10) parent(helen, _6466) Unify: (10) parent(helen, henry) Exit: (10) parent(helen, henry) Call: (10) ancestor(henry, henry) Unify: (10) ancestor(henry, henry) Call: (11) parent(henry, henry) Fail: (11) parent(henry, henry) Redo: (10) ancestor(henry, henry) Unify: (10) ancestor(henry, henry) Call: (11) parent(henry, _6466) Unify: (11) parent(henry, mary) Exit: (11) parent(henry, mary) Call: (11) ancestor(mary, henry) Unify: (11) ancestor(mary, henry) Call: (12) parent(mary, henry) Fail: (12) parent(mary, henry) Redo: (11) ancestor(mary, henry) Unify: (11) ancestor(mary, henry) Call: (12) parent(mary, _6466) Fail: (12) parent(mary, _6466) Fail: (11) ancestor(mary, henry) Fail: (10) ancestor(henry, henry) Fail: (9) ancestor(helen, henry) Fail: (8) ancestor(ann, henry) false. [trace] 11 ?- nodebug. true. 12 ?- noprotocol. ``` * * * Here is an example of using the above functions to create a basic predicate that toggles logging on and off with a single command. ```prolog % ----->>>>> toggle_trace_logging/0 % This predicate turns trace logging OFF it is currently ON, and ON if it % is OFF. Note, when logging is turned ON, any existing file with the % log file name we use is OVERWRITTEN. This can be changed by using % protcola/1 (append) instead of protocol/1. Also, this code always % writes to a file named `prolog-trace.plg` in the current working % directory. turn_off_trace_logging :- noprotocol, % Undo the changes we made to support and format trace output to % a file. leash(+all), % Show all output from the debug ports. visible(-all), set_prolog_flag(color_term, true), % Turn OFF tracing. notrace, write('Trace logging is now OFF.'), nl, !. turn_on_trace_logging :- % Establish the log file name while turning tracing ON. protocola('./prolog-trace.plg'), % Turn off color output so we don't get color characters in the % logging file. set_prolog_flag(color_term, false), % Turn off space bar confirmation for each output since we % are outputting to a file. leash(-all), % Show all output from the debug ports. visible(+all), % Turn ON tracing. notrace, write('Trace logging is now ON.'), nl, !. toggle_trace_logging :- % Is trace logging currently on? protocolling(_), % Yes. Turn it off. write('Turning OFF trace logging.'), nl, turn_off_trace_logging, !. toggle_trace_logging :- % Tracing is assumed to be OFF now. Turn it on. write('Turning ON trace logging.'), nl, turn_on_trace_logging, !. ```