Executing External Programs: what changed

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Title: Executing External Programs

New		Line
1	+	## Overview: Comparison
2	+
3	+	Here are different ways available in RTL, FCL and LCL libraries on how to execute an external command/process/program.
4	+
5	+	\| Method \| Library \| Platforms \| Single Line \| Features \|
6	+	\|----\|----\|----\|----\|----\|
7	+	\| [[Executing External Programs\|ExecuteProcess]] \| RTL \| Cross-Platform \| Yes \| Very limited, synchronous. \|
8	+	\| [[Executing External Programs\|ShellExecute]] \| WinAPI \| MS Windows only \| Yes \| Many. Can start programs with elevation/admin permissions. \|
9	+	\| [[Executing External Programs\|fpsystem, fpexecve]] \| Unix \| Unix only \| \| \|
10	+	\| [[Executing External Programs\|TProcess]] \| FCL \| Cross-Platform \| No \| Full. \|
11	+	\| [[Executing External Programs\|RunCommand]] \| FCL \| Cross-Platform Requires FPC 2.6.2+ \| Yes \| Covers common TProcess usage. \|
12	+	\| [[Executing External Programs\|OpenDocument]] \| LCL \| Cross-Platform \| Yes \| Only open document. The document would open with the application associated with that type of the document. \|
13	+	\| [[Executing External Programs\|WinExec]] \| WinAPI \| MS Windows only \| Yes Legacy option found in old Delphi code. Replace with one of the above. \| \|
14	+
15	+	## (Process.)RunCommand
16	+
17	+	- [RunCommand](http://www.freepascal.org/docs-html/fcl/process/runcommand.html) reference
18	+	- [RunCommandInDir](http://www.freepascal.org/docs-html/fcl/process/runcommandindir.html) reference
19	+
20	+	In FPC 2.6.2, some helper functions for TProcess were added to unit process based on wrappers used in the [[Projects using Lazarus\|fpcup]] project. These functions are meant for basic and intermediate use and can capture output to a single string and fully support the large output case.
21	+
22	+	A simple example is:
23	+
24	+	``` pascal
25	+	program project1;
26	+
27	+	{$mode objfpc}{$H+}
28	+
29	+	uses
30	+	Process;
31	+
32	+	var
33	+	s : ansistring;
34	+
35	+	begin
36	+
37	+	if RunCommand('/bin/bash',['-c','echo $PATH'],s) then
38	+	writeln(s);
39	+
40	+	end.
41	+	```
42	+
43	+	But note that not all shell "built-in" commands (eg alias) work because aliases by default are not expanded in non-interactive shells and .bashrc is not read by non-interactive shells unless you set the BASH_ENV environment variable. So, this does not produce any output:
44	+
45	+	``` pascal
46	+	program project2;
47	+
48	+	{$mode objfpc}{$H+}
49	+
50	+	uses
51	+	Process;
52	+
53	+	var
54	+	s : ansistring;
55	+
56	+	begin
57	+
58	+	if RunCommand('/bin/bash',['-c','alias'],s) then
59	+	writeln(s);
60	+
61	+	end.
62	+	```
63	+
64	+	An overloaded variant of RunCommand returns the exitcode of the program. The RunCommandInDir runs the command in a different directory (sets p.CurrentDirectory):
65	+
66	+	``` pascal
67	+	function RunCommandIndir(const curdir:string;const exename:string;const commands:array of string;var outputstring:string; var exitstatus:integer): integer;
68	+	function RunCommandIndir(const curdir:string;const exename:string;const commands:array of string;var outputstring:string): boolean;
69	+	function RunCommand(const exename:string;const commands:array of string;var outputstring:string): boolean;
70	+	```
71	+
72	+	In FPC 3.2.0+ the Runcommand got additional variants that allow to override TProcessOptions and WindowOptions.
73	+
74	+	### RunCommand extensions
75	+
76	+	In FPC 3.2.0+ the RunCommand implementation was generalized and integrated back into TProcess to allow for quicker construction of own variants. As an example a RunCommand variant with a timeout:
77	+
78	+	``` pascal
79	+
80	+	program TestTProcessTimeout;
81	+
82	+	uses classes, sysutils, process, dateutils;
83	+
84	+	type
85	+	{ TProcessTimeout }
86	+	TProcessTimeout = class(TProcess)
87	+	protected
88	+	timeoutperiod: TTime;
89	+	timedout : boolean;
90	+	started : TDateTime;
91	+	procedure LocalnIdleSleep(Sender,Context : TObject;status:TRunCommandEventCode;const message:string);
92	+	public
93	+	class function RunCommandwithTimeout(const exename:TProcessString;const commands:array of TProcessString;const dir:string;out outputstring:string;out errorstring:string;out exitstate:integer; ProcessOptions : TProcessOptions = [];SWOptions:TShowWindowOptions=swoNone;timeout:integer=15):boolean;static;
94	+	end;
95	+
96	+	procedure TProcessTimeout.LocalnIdleSleep(Sender,Context : TObject;status:TRunCommandEventCode;const message:string);
97	+	begin
98	+	if status=RunCommandIdle then
99	+	begin
100	+	writeln(Executable+'('+ Parameters.CommaText+')' +' time: '+TimeToStr(now-started));
101	+	if (now-started)>timeoutperiod then
102	+	begin
103	+	writeln('process timed out ');
104	+	timedout:=true;
105	+	Terminate(255);
106	+	exit;
107	+	end;
108	+	sleep(RunCommandSleepTime);
109	+	end;
110	+	end;
111	+
112	+	class function TProcessTimeout.RunCommandwithTimeout(
113	+	const exename : TProcessString;
114	+	const commands : array of TProcessString;
115	+	const dir : string;
116	+	out outputstring : string;
117	+	out errorstring : string;
118	+	out exitstate : integer;
119	+	ProcessOptions : TProcessOptions = [];
120	+	SWOptions : TShowWindowOptions=swoNone;
121	+	timeout : integer=15
122	+	):boolean;
123	+	Var
124	+	p : TProcessTimeout;
125	+	i : integer;
126	+	begin
127	+	p:=TProcessTimeout.create(nil);
128	+	p.OnRunCommandEvent:=@p.LocalnIdleSleep;
129	+	p.CurrentDirectory:=dir;
130	+
131	+	//timeout in Minutes, Check every Seconds
132	+	p.timeoutperiod:=timeout/MinsPerDay;
133	+
134	+	(*
135	+	//if you want to do the Timeout in Seconds
136	+	p.timeoutperiod:=timeout/SecsPerDay;
137	+	*)
138	+
139	+	// check every Second if finished
140	+	p.runcommandsleeptime := 1000;
141	+
142	+	if ProcessOptions<>[] then
143	+	P.Options:=ProcessOptions - [poRunSuspended,poWaitOnExit];
144	+	p.options:=p.options+[poRunIdle]; // needed to run the RUNIDLE event. See User Changes 3.2.0
145	+
146	+	P.ShowWindow:=SwOptions;
147	+	p.Executable:=exename;
148	+	if high(commands)>=0 then
149	+	for i:=low(commands) to high(commands) do
150	+	p.Parameters.add(commands[i]);
151	+	p.timedout:=false;
152	+	p.started:=now;
153	+	try
154	+	// the core loop of runcommand() variants, originally based on the "large output" scenario in the wiki, but continously expanded over 5 years.
155	+	RunCommandwithTimeout:=p.RunCommandLoop(outputstring,errorstring,exitstate)=0;
156	+	if p.timedout then
157	+	RunCommandwithTimeout:=false;
158	+	finally
159	+	p.free;
160	+	end;
161	+	if exitstate<>0 then RunCommandwithTimeout:=false;
162	+	end;
163	+
164	+	// example use:
165	+
166	+	var
167	+	output,errors : string;
168	+	exitcode :integer;
169	+	begin
170	+	//Windows and Unix have other programs that can be used
171	+	{$if defined(WINDOWS)}
172	+	if TProcessTimeout.RunCommandwithTimeout('cmd',['/c','dir','C:.exe','/s'],'c:\',output,errors,exitcode,[],swoNone,1) then // dir c:.exe /s
173	+	{$else$}
174	+	if TProcessTimeout.RunCommandwithTimeout('find',['/','-name','".sh"'],'/',output,errors,exitcode,[],swoNone,1) then // find / -name ".sh"
175	+	{$endif}
176	+	begin
177	+	writeln('program finished');
178	+	writeln('--------------------output-------------------');
179	+	writeln(output);
180	+	writeln('--------------------errors-------------------');
181	+	writeln(errors);
182	+	if not(exitcode=0) then
183	+	begin
184	+	writeln('-program finished with errors (exitcode: '+exitcode.tostring+')-');
185	+	end;
186	+	readln();
187	+	end
188	+	else
189	+	begin
190	+	writeln('program not finished');
191	+	writeln('--------------------output-------------------');
192	+	writeln(output);
193	+	writeln('--------------------errors-------------------');
194	+	writeln(errors);
195	+	writeln('-------------------EXITCODE------------------');
196	+	writeln(exitcode);
197	+	readln();
198	+	end;
199	+	end.
200	+	```
201	+
202	+	## SysUtils.ExecuteProcess
203	+
204	+	(Cross-platform)\
205	+	Despite a number of limitations, the simplest way to launch a program (modal, no pipes or any form of control) is to simply use :
206	+
207	+	``` pascal
208	+	SysUtils.ExecuteProcess(UTF8ToSys('/full/path/to/binary'), '', []);
209	+	```
210	+
211	+	The calling process runs synchronously: it 'hangs' until the external program has finished - but this may be useful if you require the user to do something before continuing in your application. For a more versatile approach, see the section about the preferred cross-platform RunCommand or other TProcess functionality, or if you only wish to target Windows you may use ShellExecute.
212	+
213	+	- [ExecuteProcess reference](http://www.freepascal.org/docs-html/rtl/sysutils/executeprocess.html)
214	+
215	+	## MS Windows: CreateProcess, ShellExecute and WinExec
216	+
217	+	> Note: While FPC/Lazarus has support for CreateProcess, ShellExecute and/or WinExec, this support is only in Win32/64. If your program is cross-platform, consider using RunCommand or TProcess.
218	+
219	+	> Note: WinExec is a 16-bit call that has been deprecated for years in the Windows API. In recent versions of FPC it generates a warning.
220	+
221	+	ShellExecute is a standard MS Windows function (ShellApi.h) with good \[<http://msdn.microsoft.com/en-us/library/windows/desktop/bb762153(v=vs.85>).aspx documentation on MSDN\] (note their remarks about initialising COM if you find the function unreliable).
222	+
223	+	``` pascal
224	+	uses ..., ShellApi;
225	+
226	+	// Simple one-liner (ignoring error returns) :
227	+	if ShellExecute(0,nil, PChar('"C:\my dir\prog.exe"'),PChar('"C:\somepath\some_doc.ext"'),nil,1) =0 then;
228	+
229	+	// Execute a Batch File :
230	+	if ShellExecute(0,nil, PChar('cmd'),PChar('/c mybatch.bat'),nil,1) =0 then;
231	+
232	+	// Open a command window in a given folder :
233	+	if ShellExecute(0,nil, PChar('cmd'),PChar('/k cd \path'),nil,1) =0 then;
234	+
235	+	// Open a webpage URL in the default browser using 'start' command (via a brief hidden cmd window) :
236	+	if ShellExecute(0,nil, PChar('cmd'),PChar('/c start www.lazarus.freepascal.org/'),nil,0) =0 then;
237	+
238	+	// or a useful procedure:
239	+	procedure RunShellExecute(const prog,params:string);
240	+	begin
241	+	// ( Handle, nil/'open'/'edit'/'find'/'explore'/'print', // 'open' isn't always needed
242	+	// path+prog, params, working folder,
243	+	// 0=hide / 1=SW_SHOWNORMAL / 3=max / 7=min) // for SW_ constants : uses ... Windows ...
244	+	if ShellExecute(0,'open',PChar(prog),PChar(params),PChar(extractfilepath(prog)),1) >32 then; //success
245	+	// return values 0..32 are errors
246	+	end;
247	+	```
248	+
249	+	There is also ShellExecuteExW as a WideChar version, and ShellExecuteExA is AnsiChar.
250	+
251	+	The fMask option can also use SEE_MASK_DOENVSUBST or SEE_MASK_FLAG_NO_UI or SEE_MASK_NOCLOSEPROCESS, etc.
252	+
253	+	If in Delphi you used ShellExecute for documents like Word documents or URLs, have a look at the open* (OpenURL etc) functions in lclintf (see the Alternatives section lower down this page).
254	+
255	+	### Using ShellExecuteEx for elevation/administrator permissions
256	+
257	+	If you need to execute external program with administrator/elevated privileges, you can use the runas method with the alternative ShellExecuteEx function:
258	+
259	+	``` pascal
260	+	uses ShellApi, ...;
261	+
262	+	function RunAsAdmin(const Handle: Hwnd; const Path, Params: string): Boolean;
263	+	var
264	+	sei: TShellExecuteInfoA;
265	+	begin
266	+	FillChar(sei, SizeOf(sei), 0);
267	+	sei.cbSize := SizeOf(sei);
268	+	sei.Wnd := Handle;
269	+	sei.fMask := SEE_MASK_FLAG_DDEWAIT or SEE_MASK_FLAG_NO_UI;
270	+	sei.lpVerb := 'runas';
271	+	sei.lpFile := PAnsiChar(Path);
272	+	sei.lpParameters := PAnsiChar(Params);
273	+	sei.nShow := SW_SHOWNORMAL;
274	+	Result := ShellExecuteExA(@sei);
275	+	end;
276	+
277	+	procedure TFormMain.RunAddOrRemoveApplication;
278	+	begin
279	+	// Example that uses elevated rundll to open the Control Panel to Programs and features
280	+	RunAsAdmin(FormMain.Handle, 'rundll32.exe shell32.dll,Control_RunDLL appwiz.cpl', '');
281	+	end;
282	+	```
283	+
284	+	## Unix fpsystem, fpexecve and shell
285	+
286	+	These functions are platform dependent.
287	+
288	+	- [fpsystem reference](http://www.freepascal.org/docs-html/rtl/unix/fpsystem.html)
289	+	- [fpexecve reference](http://www.freepascal.org/docs-html/rtl/baseunix/fpexecve.html)
290	+
291	+	Linux.Shell/Unix.Shell was an 1.0.x equivalent to fpsystem with less narrowly defined error handling, and after a decade of deprecation it was finally removed. In nearly all cases it can be replaced by fpsystem that features more POSIX like errorhandling.
292	+
293	+	## TProcess
294	+
295	+	You can use TProcess to launch external programs. Some of the benefits of using TProcess are that it is:
296	+
297	+	- Platform Independent
298	+	- Capable of reading from stdout and writing to stdin.
299	+	- Possible to wait for a command to finish or let it run while your program moves on.
300	+
301	+	Important notes:
302	+
303	+	- TProcess is not a terminal/shell! You cannot directly execute scripts or redirect output using operators like "\\|", "\>", "\<", "&" etc. It is possible to obtain the same results with TProcess using pascal, some examples are below..
304	+	- Presumably on Linux/Unix: you must specify the full path to the executable. For example '/bin/cp' instead of 'cp'. If the program is in the standard PATH then you can use the function [[doc:lcl/fileutil/finddefaultexecutablepath.html\|FindDefaultExecutablePath]] from the [[doc:lcl/fileutil/index.html\|FileUtil]] unit of the LCL.
305	+	- On Windows, if the command is in the path, you don't need to specify the full path.
306	+	- [[doc:fcl/process/tprocess.html\|TProcess reference]]
307	+
308	+	### The Simplest Example
309	+
310	+	A lot of typical cases have been prepared in the [[Executing External Programs\|Runcommand]] functions. Before you start copy and paste the examples below, check them out first.
311	+
312	+	### A Simple Example
313	+
314	+	This example (that shouldn't be used in production, see Large Output or, better, [[Executing External Programs\|Runcommand]]) just shows you how to run an external program, nothing more:
315	+
316	+	``` pascal
317	+	// This is a demo program that shows
318	+	// how to launch an external program.
319	+	program launchprogram;
320	+
321	+	// Here we include files that have useful functions
322	+	// and procedures we will need.
323	+	uses
324	+	Classes, SysUtils, Process;
325	+
326	+	// This defines the var "AProcess" as a variable
327	+	// of the type "TProcess"
328	+	var
329	+	AProcess: TProcess;
330	+
331	+	// This is where our program starts to run
332	+	begin
333	+	// Now we will create the TProcess object, and
334	+	// assign it to the var AProcess.
335	+	AProcess := TProcess.Create(nil);
336	+
337	+	// Tell the new AProcess what the command to execute is.
338	+	// Let's use the Free Pascal compiler (i386 version that is)
339	+	AProcess.Executable:= 'ppc386';
340	+
341	+	// Pass -h together with ppc386 so actually 'ppc386 -h' is executed:
342	+	AProcess.Parameters.Add('-h');
343	+
344	+	// We will define an option for when the program
345	+	// is run. This option will make sure that our program
346	+	// does not continue until the program we will launch
347	+	// has stopped running. vvvvvvvvvvvvvv
348	+	AProcess.Options := AProcess.Options + [poWaitOnExit];
349	+
350	+	// Now let AProcess run the program
351	+	AProcess.Execute;
352	+
353	+	// This is not reached until ppc386 stops running.
354	+	AProcess.Free;
355	+	end.
356	+	```
357	+
358	+	That's it! You have just learned to run an external program from inside your own program.
359	+
360	+	### An improved example (but not correct yet)
361	+
362	+	That's nice, but how do I read the Output of a program that I have run?
363	+
364	+	Well, let's expand our example a little and do just that: This example is kept simple so you can learn from it. Please don't use this example in production code, but use the code in #Reading large output.
365	+
366	+	``` pascal
367	+	// This is a
368	+	// FLAWED
369	+	// demo program that shows
370	+	// how to launch an external program
371	+	// and read from its output.
372	+	program launchprogram;
373	+
374	+	// Here we include files that have useful functions
375	+	// and procedures we will need.
376	+	uses
377	+	Classes, SysUtils, Process;
378	+
379	+	// This is defining the var "AProcess" as a variable
380	+	// of the type "TProcess"
381	+	// Also now we are adding a TStringList to store the
382	+	// data read from the programs output.
383	+	var
384	+	AProcess: TProcess;
385	+	AStringList: TStringList;
386	+
387	+	// This is where our program starts to run
388	+	begin
389	+	// Now we will create the TProcess object, and
390	+	// assign it to the var AProcess.
391	+	AProcess := TProcess.Create(nil);
392	+
393	+	// Tell the new AProcess what the command to execute is.
394	+	AProcess.Executable := '/usr/bin/ppc386';
395	+	AProcess.Parameters.Add('-h');
396	+
397	+	// We will define an option for when the program
398	+	// is run. This option will make sure that our program
399	+	// does not continue until the program we will launch
400	+	// has stopped running. Also now we will tell it that
401	+	// we want to read the output of the file.
402	+	AProcess.Options := AProcess.Options + [poWaitOnExit, poUsePipes];
403	+
404	+	// Now that AProcess knows what the commandline is it can be run.
405	+	AProcess.Execute;
406	+
407	+	// After AProcess has finished, the rest of the program will be executed.
408	+
409	+	// Now read the output of the program we just ran into a TStringList.
410	+	AStringList := TStringList.Create;
411	+	AStringList.LoadFromStream(AProcess.Output);
412	+
413	+	// Save the output to a file and clean up the TStringList.
414	+	AStringList.SaveToFile('output.txt');
415	+	AStringList.Free;
416	+
417	+	// Now that the output from the process is processed, it can be freed.
418	+	AProcess.Free;
419	+	end.
420	+	```
421	+
422	+	### Reading large output
423	+
424	+	In the previous example we waited until the program exited. Then we read what the program has written to its output.
425	+
426	+	Suppose the program writes a lot of data to the output. Then the output pipe becomes full and the called progam waits until the pipe has been read from.
427	+
428	+	But the calling program doesn't read from it until the called program has ended. A deadlock occurs.
429	+
430	+	The following example therefore doesn't use poWaitOnExit, but reads from the output while the program is still running. The output is stored in a memory stream, that can be used later to read the output into a TStringList.
431	+
432	+	If you want to read output from an external process, and can't use RunCommand, this is the code you should as a base for production use. If you are using FPC 3.2.0+ a parametrisable form of this loop is available as the method RunCommandLoop in TProcess. An event OnRunCommandEvent can be hooked to further modify the behaviour.
433	+
434	+	``` pascal
435	+	program LargeOutputDemo;
436	+
437	+	{$mode objfpc}{$H+}
438	+
439	+	uses
440	+	Classes, SysUtils, Process; // Process is the unit that holds TProcess
441	+
442	+	const
443	+	BUF_SIZE = 2048; // Buffer size for reading the output in chunks
444	+
445	+	var
446	+	AProcess : TProcess;
447	+	OutputStream : TStream;
448	+	BytesRead : longint;
449	+	Buffer : array[1..BUF_SIZE] of byte;
450	+
451	+	begin
452	+	// Set up the process; as an example a recursive directory search is used
453	+	// because that will usually result in a lot of data.
454	+	AProcess := TProcess.Create(nil);
455	+
456	+	// The commands for Windows and *nix are different hence the $IFDEFs
457	+	{$IFDEF Windows}
458	+	// In Windows the dir command cannot be used directly because it's a build-in
459	+	// shell command. Therefore cmd.exe and the extra parameters are needed.
460	+	AProcess.Executable := 'c:\windows\system32\cmd.exe';
461	+	AProcess.Parameters.Add('/c');
462	+	AProcess.Parameters.Add('dir /s c:\windows');
463	+	{$ENDIF Windows}
464	+
465	+	{$IFDEF Unix}
466	+	AProcess.Executable := '/bin/ls';
467	+
468	+	{$IFDEF Darwin}
469	+	AProcess.Parameters.Add('-recursive');
470	+	AProcess.Parameters.Add('-all');
471	+	{$ENDIF Darwin}
472	+
473	+	{$IFDEF Linux}
474	+	AProcess.Parameters.Add('--recursive');
475	+	AProcess.Parameters.Add('--all');
476	+	{$ENDIF Linux}
477	+
478	+	{$IFDEF FreeBSD}
479	+	AProcess.Parameters.Add('-R');
480	+	AProcess.Parameters.Add('-a');
481	+	{$ENDIF FreeBSD}
482	+
483	+	AProcess.Parameters.Add('-l');
484	+	{$ENDIF Unix}
485	+
486	+	// Process option poUsePipes has to be used so the output can be captured.
487	+	// Process option poWaitOnExit can not be used because that would block
488	+	// this program, preventing it from reading the output data of the process.
489	+	AProcess.Options := [poUsePipes];
490	+
491	+	// Start the process (run the dir/ls command)
492	+	AProcess.Execute;
493	+
494	+	// Create a stream object to store the generated output in. This could
495	+	// also be a file stream to directly save the output to disk.
496	+	OutputStream := TMemoryStream.Create;
497	+
498	+	// All generated output from AProcess is read in a loop until no more data is available
499	+	repeat
500	+	// Get the new data from the process to a maximum of the buffer size that was allocated.
501	+	// Note that all read(...) calls will block except for the last one, which returns 0 (zero).
502	+	BytesRead := AProcess.Output.Read(Buffer, BUF_SIZE);
503	+
504	+	// Add the bytes that were read to the stream for later usage
505	+	OutputStream.Write(Buffer, BytesRead)
506	+
507	+	until BytesRead = 0; // Stop if no more data is available
508	+
509	+	// The process has finished so it can be cleaned up
510	+	AProcess.Free;
511	+
512	+	// Now that all data has been read it can be used; for example to save it to a file on disk
513	+	with TFileStream.Create('output.txt', fmCreate) do
514	+	begin
515	+	OutputStream.Position := 0; // Required to make sure all data is copied from the start
516	+	CopyFrom(OutputStream, OutputStream.Size);
517	+	Free
518	+	end;
519	+
520	+	// Or the data can be shown on screen
521	+	with TStringList.Create do
522	+	begin
523	+	OutputStream.Position := 0; // Required to make sure all data is copied from the start
524	+	LoadFromStream(OutputStream);
525	+	writeln(Text);
526	+	writeln('--- Number of lines = ', Count, '----');
527	+	Free
528	+	end;
529	+
530	+	// Clean up
531	+	OutputStream.Free;
532	+	end.
533	+	```
534	+
535	+	Note that the above could also be accomplished by using RunCommand:
536	+
537	+	``` pascal
538	+	var s: string;
539	+	...
540	+	RunCommand('c:\windows\system32\cmd.exe', ['/c', 'dir /s c:\windows'], s);
541	+	```
542	+
543	+	### Using input and output of a TProcess
544	+
545	+	See processdemo example in the [Lazarus-CCR SVN](https://sourceforge.net/p/lazarus-ccr/svn/HEAD/tree/examples/process).
546	+
547	+	### Hints on the use of TProcess
548	+
549	+	When creating a cross-platform program, the OS-specific executable name can be set using directives "{\$IFDEF}" and "{\$ENDIF}".
550	+
551	+	Example:
552	+
553	+	``` pascal
554	+	{...}
555	+	AProcess := TProcess.Create(nil)
556	+
557	+	{$IFDEF WIN32}
558	+	AProcess.Executable := 'calc.exe';
559	+	{$ENDIF}
560	+
561	+	{$IFDEF LINUX}
562	+	AProcess.Executable := FindDefaultExecutablePath('kcalc');
563	+	{$ENDIF}
564	+
565	+	AProcess.Execute;
566	+	{...}
567	+	```
568	+
569	+	### macOS show application bundle in foreground
570	+
571	+	You can start an application bundle via TProcess by starting the executable within the bundle. For example:
572	+
573	+	``` pascal
574	+	AProcess.Executable:='/Applications/iCal.app/Contents/MacOS/iCal';
575	+	```
576	+
577	+	This will start the Calendar, but the window will be behind the current application. To get the application in the foreground you can use the open utility with the -n parameter:
578	+
579	+	``` pascal
580	+	AProcess.Executable:='/usr/bin/open';
581	+	AProcess.Parameters.Add('-n');
582	+	AProcess.Parameters.Add('-a'); // optional: specifies the application to use; only searches the Application directories
583	+	AProcess.Parameters.Add('-W'); // optional: open waits until the applications it opens (or were already open) have exited
584	+	AProcess.Parameters.Add('Pages.app'); // including .app is optional
585	+	```
586	+
587	+	If your application needs parameters, you can pass open the --args parameter, after which all parameters are passed to the application:
588	+
589	+	``` pascal
590	+	AProcess.Parameters.Add('--args');
591	+	AProcess.Parameters.Add('argument1');
592	+	AProcess.Parameters.Add('argument2');
593	+	```
594	+
595	+	See also: [[macOS Open Sesame\|macOS open command]].
596	+
597	+	### Run detached program
598	+
599	+	Normally a program started by your application is a child process and is killed, when your application is killed. When you want to run a standalone program that keeps running, you can use the following:
600	+
601	+	``` pascal
602	+	var
603	+	Process: TProcess;
604	+	I: Integer;
605	+	begin
606	+	Process := TProcess.Create(nil);
607	+	try
608	+	Process.InheritHandles := False;
609	+	Process.Options := [];
610	+	Process.ShowWindow := swoShow;
611	+
612	+	// Copy default environment variables including DISPLAY variable for GUI application to work
613	+	for I := 1 to GetEnvironmentVariableCount do
614	+	Process.Environment.Add(GetEnvironmentString(I));
615	+
616	+	Process.Executable := '/usr/bin/gedit';
617	+	Process.Execute;
618	+	finally
619	+	Process.Free;
620	+	end;
621	+	end;
622	+	```
623	+
624	+	### Example of "talking" with aspell process
625	+
626	+	Inside [pasdoc](https://github.com/pasdoc/pasdoc/wiki) source code you can find two units that perform spell-checking by "talking" with running aspell process through pipes:
627	+
628	+	- [PasDoc_ProcessLineTalk.pas unit](https://github.com/pasdoc/pasdoc/blob/master/source/component/PasDoc_ProcessLineTalk.pas) implements TProcessLineTalk class, descendant of TProcess, that can be easily used to talk with any process on a line-by-line basis.
629	+
630	+	- [PasDoc_Aspell.pas units](https://github.com/pasdoc/pasdoc/blob/master/source/component/PasDoc_Aspell.pas) implements TAspellProcess class, that performs spell-checking by using underlying TProcessLineTalk instance to execute aspell and communicate with running aspell process.
631	+
632	+	Both units are rather independent from the rest of pasdoc sources, so they may serve as real-world examples of using TProcess to run and communicate through pipes with other program.
633	+
634	+	### Replacing shell operators like "\\| \< \>"
635	+
636	+	Sometimes you want to run a more complicated command that pipes its data to another command or to a file. Something like
637	+
638	+	``` pascal
639	+	ShellExecute('firstcommand.exe \| secondcommand.exe');
640	+	```
641	+
642	+	or
643	+
644	+	``` pascal
645	+	ShellExecute('dir > output.txt');
646	+	```
647	+
648	+	Executing this with TProcess will not work. i.e:
649	+
650	+	``` pascal
651	+	// this won't work
652	+	Process.CommandLine := 'firstcommand.exe \| secondcommand.exe';
653	+	Process.Execute;
654	+	```
655	+
656	+	#### Why using special operators to redirect output doesn't work
657	+
658	+	TProcess is just that, it's not a shell environment, only a process. It's not two processes, it's only one. It is possible to redirect output however just the way you wanted. See the [[Executing External Programs\|next section]].
659	+
660	+	### How to redirect output with TProcess
661	+
662	+	You can redirect the output of a command to another command by using a TProcess instance for each command.
663	+
664	+	Here's an example that explains how to redirect the output of one process to another. To redirect the output of a process to a file/stream see the example [[Executing External Programs\|Reading Large Output]]
665	+
666	+	Not only can you redirect the "normal" output (also known as stdout), but you can also redirect the error output (stderr), if you specify the poStderrToOutPut option, as seen in the options for the second process.
667	+
668	+	``` pascal
669	+	program Project1;
670	+
671	+	uses
672	+	Classes, sysutils, process;
673	+
674	+	var
675	+	FirstProcess,
676	+	SecondProcess: TProcess;
677	+	Buffer: array[0..127] of char;
678	+	ReadCount: Integer;
679	+	ReadSize: Integer;
680	+	begin
681	+	FirstProcess := TProcess.Create(nil);
682	+	SecondProcess := TProcess.Create(nil);
683	+
684	+	FirstProcess.Options := [poUsePipes];
685	+	FirstProcess.Executable := 'pwd';
686	+
687	+	SecondProcess.Options := [poUsePipes,poStderrToOutPut];
688	+	SecondProcess.Executable := 'grep';
689	+	SecondProcess.Parameters.Add(DirectorySeparator+ ' -');
690	+	// this would be the same as "pwd \| grep / -"
691	+
692	+	FirstProcess.Execute;
693	+	SecondProcess.Execute;
694	+
695	+	while FirstProcess.Running or (FirstProcess.Output.NumBytesAvailable > 0) do
696	+	begin
697	+	if FirstProcess.Output.NumBytesAvailable > 0 then
698	+	begin
699	+	// make sure that we don't read more data than we have allocated
700	+	// in the buffer
701	+	ReadSize := FirstProcess.Output.NumBytesAvailable;
702	+	if ReadSize > SizeOf(Buffer) then
703	+	ReadSize := SizeOf(Buffer);
704	+	// now read the output into the buffer
705	+	ReadCount := FirstProcess.Output.Read(Buffer[0], ReadSize);
706	+	// and write the buffer to the second process
707	+	SecondProcess.Input.Write(Buffer[0], ReadCount);
708	+
709	+	// if SecondProcess writes much data to it's Output then
710	+	// we should read that data here to prevent a deadlock
711	+	// see the previous example "Reading Large Output"
712	+	end;
713	+	end;
714	+	// Close the input on the SecondProcess
715	+	// so it finishes processing it's data
716	+	SecondProcess.CloseInput;
717	+
718	+	// and wait for it to complete
719	+	// be carefull what command you run because it may not exit when
720	+	// it's input is closed and the following line may loop forever
721	+	while SecondProcess.Running do
722	+	Sleep(1);
723	+	// that's it! the rest of the program is just so the example
724	+	// is a little 'useful'
725	+
726	+	// we will reuse Buffer to output the SecondProcess's
727	+	// output to this programs stdout
728	+	WriteLn('Grep output Start:');
729	+	ReadSize := SecondProcess.Output.NumBytesAvailable;
730	+	if ReadSize > SizeOf(Buffer) then
731	+	ReadSize := SizeOf(Buffer);
732	+	if ReadSize > 0 then
733	+	begin
734	+	ReadCount := SecondProcess.Output.Read(Buffer, ReadSize);
735	+	WriteLn(Copy(Buffer,0, ReadCount));
736	+	end
737	+	else
738	+	WriteLn('grep did not find what we searched for. ', SecondProcess.ExitStatus);
739	+	WriteLn('Grep output Finish:');
740	+
741	+	// free our process objects
742	+	FirstProcess.Free;
743	+	SecondProcess.Free;
744	+	end.
745	+	```
746	+
747	+	That's it. Now you can redirect output from one program to another.
748	+
749	+	#### Notes
750	+
751	+	This example may seem overdone since it's possible to run "complicated" commands using a shell with TProcess like:
752	+
753	+	``` pascal
754	+	Process.Commandline := 'sh -c "pwd \| grep / -"';
755	+	```
756	+
757	+	But our example is more crossplatform since it needs no modification to run on Windows or Linux etc. "sh" may or may not exist on your platform and is generally only available on *nix platforms. Also we have more flexibility in our example since you can read and write from/to the input, output and stderr of each process individually, which could be very advantageous for your project.
758	+
759	+	### Redirecting input and output and running under root
760	+
761	+	A common problem on Unixes (FreeBSD, macOS) and Linux is that you want to execute some program under the root account (or, more generally, another user account). An example would be running the ping command.
762	+
763	+	If you can use sudo for this, you could adapt the following example adapted from one posted by andyman on the forum ([1](http://lazarus.freepascal.org/index.php/topic,14479.0.html)). This sample runs `ls` on the `/root` directory, but can of course be adapted.
764	+
765	+	A better way to do this is to use the policykit package, which should be available on all recent Linuxes. [See the forum thread for details.](http://lazarus.freepascal.org/index.php/topic,14479.0.html)
766	+
767	+	Large parts of this code are similar to the earlier example, but it also shows how to redirect stdout and stderr of the process being called separately to stdout and stderr of our own code.
768	+
769	+	``` pascal
770	+	program rootls;
771	+
772	+	{ Demonstrates using TProcess, redirecting stdout/stderr to our stdout/stderr,
773	+	calling sudo on FreeBSD/Linux/macOS, and supplying input on stdin}
774	+	{$mode objfpc}{$H+}
775	+
776	+	uses
777	+	Classes,
778	+	Math, {for min}
779	+	Process;
780	+
781	+	procedure RunsLsRoot;
782	+	var
783	+	Proc: TProcess;
784	+	CharBuffer: array [0..511] of char;
785	+	ReadCount: integer;
786	+	ExitCode: integer;
787	+	SudoPassword: string;
788	+	begin
789	+	WriteLn('Please enter the sudo password:');
790	+	Readln(SudoPassword);
791	+	ExitCode := -1; //Start out with failure, let's see later if it works
792	+	Proc := TProcess.Create(nil); //Create a new process
793	+	try
794	+	Proc.Options := [poUsePipes, poStderrToOutPut]; //Use pipes to redirect program stdin,stdout,stderr
795	+	Proc.CommandLine := 'sudo -S ls /root'; //Run ls /root as root using sudo
796	+	// -S causes sudo to read the password from stdin.
797	+	Proc.Execute; //start it. sudo will now probably ask for a password
798	+
799	+	// write the password to stdin of the sudo program:
800	+	SudoPassword := SudoPassword + LineEnding;
801	+	Proc.Input.Write(SudoPassword[1], Length(SudoPassword));
802	+	SudoPassword := '%*'; //short string, hope this will scramble memory a bit; note: using PChars is more fool-proof
803	+	SudoPassword := ''; // and make the program a bit safer from snooping?!?
804	+
805	+	// main loop to read output from stdout and stderr of sudo
806	+	while Proc.Running or (Proc.Output.NumBytesAvailable > 0) or
807	+	(Proc.Stderr.NumBytesAvailable > 0) do
808	+	begin
809	+	// read stdout and write to our stdout
810	+	while Proc.Output.NumBytesAvailable > 0 do
811	+	begin
812	+	ReadCount := Min(512, Proc.Output.NumBytesAvailable); //Read up to buffer, not more
813	+	Proc.Output.Read(CharBuffer, ReadCount);
814	+	Write(StdOut, Copy(CharBuffer, 0, ReadCount));
815	+	end;
816	+	// read stderr and write to our stderr
817	+	while Proc.Stderr.NumBytesAvailable > 0 do
818	+	begin
819	+	ReadCount := Min(512, Proc.Stderr.NumBytesAvailable); //Read up to buffer, not more
820	+	Proc.Stderr.Read(CharBuffer, ReadCount);
821	+	Write(StdErr, Copy(CharBuffer, 0, ReadCount));
822	+	end;
823	+	end;
824	+	ExitCode := Proc.ExitStatus;
825	+	finally
826	+	Proc.Free;
827	+	Halt(ExitCode);
828	+	end;
829	+	end;
830	+
831	+	begin
832	+	RunsLsRoot;
833	+	end.
834	+	```
835	+
836	+	Other thoughts: It would no doubt be advisable to see if sudo actually prompts for a password. This can be checked consistently by setting the environment variable SUDO_PROMPT to something we watch for while reading the stdout of TProcess avoiding the problem of the prompt being different for different locales. Setting an environment variable causes the default values to be cleared(inherited from our process) so we have to copy the environment from our program if needed.
837	+
838	+	### Using fdisk with sudo on Linux
839	+
840	+	The following example shows how to run fdisk on a Linux machine using the sudo command to get root permissions. Note: this is an example only, and does not cater for large output.
841	+
842	+	``` pascal
843	+	program getpartitioninfo;
844	+	{Originally contributed by Lazarus forums wjackon153. Please contact him for questions, remarks etc.
845	+	Modified from Lazarus snippet to FPC program for ease of understanding/conciseness by BigChimp}
846	+
847	+	Uses
848	+	Classes, SysUtils, FileUtil, Process;
849	+
850	+	var
851	+	hprocess: TProcess;
852	+	sPass: String;
853	+	OutputLines: TStringList;
854	+
855	+	begin
856	+	sPass := 'yoursudopasswordhere'; // You need to change this to your own sudo password
857	+	OutputLines:=TStringList.Create; //... a try...finally block would be nice to make sure
858	+	// OutputLines is freed... Same for hProcess.
859	+
860	+	// The following example will open fdisk in the background and give us partition information
861	+	// Since fdisk requires elevated priviledges we need to
862	+	// pass our password as a parameter to sudo using the -S
863	+	// option, so it will will wait till our program sends our password to the sudo application
864	+	hProcess := TProcess.Create(nil);
865	+	// On Linux/Unix/FreeBSD/macOS, we need specify full path to our executable:
866	+	hProcess.Executable := '/bin/sh';
867	+	// Now we add all the parameters on the command line:
868	+	hprocess.Parameters.Add('-c');
869	+	// Here we pipe the password to the sudo command which then executes fdisk -l:
870	+	hprocess.Parameters.add('echo ' + sPass + ' \| sudo -S fdisk -l');
871	+	// Run asynchronously (wait for process to exit) and use pipes so we can read the output pipe
872	+	hProcess.Options := hProcess.Options + [poWaitOnExit, poUsePipes];
873	+	// Now run:
874	+	hProcess.Execute;
875	+
876	+	// hProcess should have now run the external executable (because we use poWaitOnExit).
877	+	// Now you can process the process output (standard output and standard error), eg:
878	+	OutputLines.Add('stdout:');
879	+	OutputLines.LoadFromStream(hprocess.Output);
880	+	OutputLines.Add('stderr:');
881	+	OutputLines.LoadFromStream(hProcess.Stderr);
882	+	// Show output on screen:
883	+	writeln(OutputLines.Text);
884	+
885	+	// Clean up to avoid memory leaks:
886	+	hProcess.Free;
887	+	OutputLines.Free;
888	+
889	+	//Below are some examples as you see we can pass illegal characters just as if done from terminal
890	+	//Even though you have read elsewhere that you can not I assure with this method you can :)
891	+
892	+	//hprocess.Parameters.Add('ping -c 1 www.google.com');
893	+	//hprocess.Parameters.Add('ifconfig wlan0 \| grep ' + QuotedStr('inet addr:') + ' \| cut -d: -f2');
894	+
895	+	//Using QuotedStr() is not a requirement though it makes for cleaner code;
896	+	//you can use double quote and have the same effect.
897	+
898	+	//hprocess.Parameters.Add('glxinfo \| grep direct');
899	+
900	+	// This method can also be used for installing applications from your repository:
901	+
902	+	//hprocess.Parameters.add('echo ' + sPass + ' \| sudo -S apt-get install -y pkg-name');
903	+
904	+	end.
905	+	```
906	+
907	+	### Parameters which contain spaces (Replacing Shell Quotes)
908	+
909	+	In the Linux shell it is possible to write quoted arguments like this:
910	+
911	+	`gdb --batch --eval-command="info symbol 0x0000DDDD" myprogram`
912	+
913	+	And GDB will receive 3 arguments (in addition to the first argument which is the full path to the executable):
914	+
915	+	1. --batch
916	+	2. --eval-command=info symbol 0x0000DDDD
917	+	3. the full path to myprogram
918	+
919	+	The best solution to avoid complicated quoting is to to switch to TProcess.Parameters.Add instead of setting the Commandline for non trivial cases e.g.
920	+
921	+	` AProcess.Executable:='/usr/bin/gdb';`\
922	+	` AProcess.Parameters.Add('--batch');`\
923	+	` AProcess.Parameters.Add('--eval-command=info symbol 0x0000DDDD'); // note the absence of quoting here`\
924	+	` AProcess.Parameters.Add('/home/me/myprogram');`
925	+
926	+	And also remember to only pass full paths.
927	+
928	+	TProcess.Commandline however does support some basic quoting for parameters with quoting. Quote the whole parameter containing spaces with double quotes. Like this:
929	+
930	+	`AProcess.CommandLine := '/usr/bin/gdb --batch "--eval-command=info symbol 0x0000DDDD" /home/me/myprogram';`
931	+
932	+	The .CommandLine property is [deprecated](http://bugs.freepascal.org/view.php?id=14446) and bugreports to support more complicated quoting cases won't accepted.
933	+
934	+	## LCLIntf Alternatives
935	+
936	+	Sometimes, you don't need to explicitly call an external program to get the functionality you need. Instead of opening an application and specifying the document to go with it, just ask the OS to open the document and let it use the default application associated with that file type. Below are some examples.
937	+
938	+	### Open document in default application
939	+
940	+	In some situations you need to open some document/file using default associated application rather than execute a particular program. This depends on running operating system. Lazarus provides a platform independent procedure OpenDocument which will handle it for you. Your application will continue running without waiting for the document process to close.
941	+
942	+	``` pascal
943	+	uses LCLIntf;
944	+	...
945	+	OpenDocument('manual.pdf');
946	+	...
947	+	```
948	+
949	+	- [[opendocument\|OpenDocument reference]]
950	+
951	+	### Open web page in default web browser
952	+
953	+	Just pass the URL required, the leading <http://> appears to be optional under certain circumstances. Also, passing a filename appears to give the same results as OpenDocument()
954	+
955	+	``` pascal
956	+	uses LCLIntf;
957	+	...
958	+	OpenURL('www.lazarus.freepascal.org/');
959	+	```
960	+
961	+	See also:
962	+
963	+	- [[OpenURL\|OpenURL reference]]
964	+
965	+	Or, you could use TProcess like this:
966	+
967	+	``` pascal
968	+	uses Process;
969	+
970	+	procedure OpenWebPage(URL: string);
971	+	// Apparently you need to pass your URL inside ", like "www.lazarus.freepascal.org"
972	+	var
973	+	Browser, Params: string;
974	+	begin
975	+	FindDefaultBrowser(Browser, Params);
976	+	with TProcess.Create(nil) do
977	+	try
978	+	Executable := Browser;
979	+	Params:=Format(Params, [URL]);
980	+	Params:=copy(Params,2,length(Params)-2); // remove "", the new version of TProcess.Parameters does that itself
981	+	Parameters.Add(Params);
982	+	Options := [poNoConsole];
983	+	Execute;
984	+	finally
985	+	Free;
986	+	end;
987	+	end;
988	+	```
989	+
990	+	## WinExec
991	+
992	+	The Windows 3.x precursor of CreateProcess, sometimes still encountered in ancient Delphi code. Replace with one of the above. It is still available in unit Windows, but marked deprecated
993	+
994	+	## See also
995	+
996	+	- [TProcess documentation](http://lazarus-ccr.sourceforge.net/docs/fcl/process/tprocess.html)
997	+	- [[opendocument\|OpenDocument]]
998	+	- [[OpenURL]]
999	+	- [[TProcessUTF8]]
1000	+	- [[TXMLPropStorage]]
1001	+	- [[Webbrowser]]
1002	+
1003	+	---
1004	+	From the Free Pascal wiki, page "Executing External Programs", as it stood on 2023-09-19 after a change by Marcov, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).

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