AmigaDos.SystemTagList()
This documentation will first of all focus on running a command using the shell and doing so in an asynchrone matter. At the same time it tries to catch the output of that executed command, using the pipefs handler in AROS.
Caveats: There is little documentation at all concerning this topic, let alone for AROS in specific. So, whenever there is some documentation, you have to read that literally and fill in the blanks yourself. Hopefully this documentation is able to fill in some of those blanks.
Introduction
As can be read in the AutoDocs, the SystemTagList() function provides a way to execute a command via the shell. But what is not so evident, is that there are some caveats as well as some undocumented features that are not very well described.
Parameters
Let's start with the parameters that can be passed to this function.
The tags
[Insert here explaination about the tags]
Piping
Who fiddled the piper ?
How to use SystemTagList() in practise
Executing shell commands using SystemTagList():
- #Synchrone
- #Synchrone and hidden
- #Synchrone, hidden and catching Output
- #Synchrone, hidden, catching Output as well as Errors
- #Executing Asynchrone and catching Output
- #Executing Asynchrone and catching Output as well as Error
Synchrone
[insert explanation here] [insert example here]
[insert explanation here] [insert example here]
[insert explanation here] [insert example here]
[insert explanation here] [insert example here]
Executing Asynchrone and catching Output.
[insert explanation here]
[paste example here]
Program RunCMDoo;
{
Name : RunCMDoo V0.1
Target : AROS ABIv0/i386
Author : n/a
Date : 2013-09-15
Goal : Run a command using SystemTagList() and catch its output
Usage : RunCMDoo Command "[parameter1 parameter2 parameterN]"
}
{$MODE OBJFPC}{$H+}
Uses
exec, amigados, utility, tagsarray;
Type
BPTR = LongInt; // Quick fix to compensate for pointer
TRCMode =
(
rcm_output, // Only use SYS_Output
rcm_combined, // Use Sys_Output and Sys_Error using the same handle.
// (impossible using SystemTagList() ?)
rcm_both // use SYS_Output and Sys_Error both using their own handle.
// (currently bugs)
);
Var
CommandHasEnded : boolean = false;
CommandExitCode : longint = 0;
CommandSegList : BPTR = 0;
Var
OutPipeRead : BPTR;
OutPipeWrite : BPTR;
Const
OutPipeName = 'PIPEFS:CmdOut'; // Name should be randomized or use * (* = untested)
Procedure CMDExitCode(retcode: LongInt; SegList: BPTR); cdecl;
begin
Writeln('Enter - MyExitCode()');
CommandHasEnded := true;
CommandExitCode := retcode;
CommandSegList := SegList;
Writeln('MyExitCode(): exitcode =', CommandExitCode);
Writeln('MyExitCode(): seglist =', CommandSegList);
Writeln('Leave - MyExitCode()');
end;
Procedure RunCMDOutput(CommandToRun: String);
var
TagsList : TTagsList = nil;
Tags : pTagItem;
res : LongInt;
nread : LongInt;
OutPipeBuffer : packed array[0..255] of char;
begin
OutPipeWrite := DosOpen( OutPipeName , MODE_READWRITE);
if (OutPipeWrite <> 0) then
begin
addtags(TagsList,
[
LONG(SYS_Input) , nil,
LONG(SYS_Output) , OutPipeWrite,
LONG(NP_CloseOutput) , 1,
LONG(SYS_Error) , nil,
LONG(SYS_Asynch) , 1,
LONG(SYS_BackGround) , 1,
LONG(NP_ExitCode) , @CMDExitCode,
TAG_DONE
]);
Tags := GetTagPtr(TagsList);
writeln('RUNCMD(): Executing SystemTagList()');
res := SystemTagList(CommandToRun, Tags);
If (res <> -1) then
begin
writeln('RUNCMD(): SystemTagList() returned value ', res);
writeln('RUNCMD(): opening OutPipe for reading');
OutPipeRead := DosOpen( OutPipeName , MODE_OLDFILE);
if (OutPipeRead <> 0) then
begin
writeln('RUNCMD(): entering main loop for reading data from OutPipe');
while true do
begin
writeln('RUNCMD(): start a buffer read from OutPipe');
nread := DosRead(OutPipeRead, @OutPipeBuffer[0], 255);
// -1 = error, 0 = EOF and >0 = number of bytes actually read.
if (nread <> -1) then
begin
writeln('RUNCMD(): buffer read from OutPipe was succesfull');
OutPipeBuffer[nread] := #0;
writeln(pchar(OutPipeBuffer));
if (nread < 255) then break;
end
else
begin
writeln('RUNCMD(): ERROR - buffer read failed, IoErr() = ', IoErr);
break;
end;
// Safety check ?
if CommandHasEnded then Break;
end;
writeln('RUNCMD(): exiting main loop that read data from OutPipe');
// Close our Output Pipe reader.
DOSClose(OutPipeRead);
end
else writeln('RUNCMD(): ERROR - Failed to open pipe for read acces');
end
else writeln('RUNCMD(): ERROR - Failed to execute command');
// close outputwrite when error occurend when executing systemtags()
end;
end;
Procedure RunCommand(CommandToRun: String; RCMode: TRCMode);
begin
writeln('enter - runcommmand');
case RCMode of
rcm_output : RunCMDOutput(CommandToRun);
// rcm_combined : RunCMDCombined(CommandToRun);
// rcm_Both : RunCMDBoth(CommandToRun);
end; // case;
writeln('leave - runcommmand');
end;
(*
MAIN
*)
var
i : Integer;
S : String = '';
begin
writeln('enter');
If paramcount > 0 then
begin
for i := 1 to paramcount
do S := S + Paramstr(i) + ' ';
Writeln('Trying to execute command "',S,'"');
RunCommand(S, rcm_Output);
end
else // Show usage/examples
begin
Writeln('RunCMDoo v0.1');
Writeln;
Writeln('usage:');
Writeln(' RunCMDoo Command [Parameter1 Paramere2 ParamterN]');
Writeln;
Writeln('example:');
Writeln(' RunCMDoo LD --help');
Writeln(' RunCMDoo LD --wrong_parameter_on_purpose');
Writeln(' RunCMDoo LD -v');
Writeln(' RunCMDoo dir ram:#?');
Writeln;
end;
writeln('leave');
end.
Executing Asynchrone and catching Output as well as Error
[insert explanation here]
Current problems: Unable to determine which pipe needs to be read first, so in the end one would always end up in a deadlock because not knowing what comes first OutPut or Error. Choosing the wrong one would make you wait forever and can only be 'broken' by reading the other pipe (flushing did not help).
Unable to:
- use WaitForChar() as pipes are not in raw mode
- unable to use fib for size of pipe as a pipe-file is always zero
[insert example here]