Execute external program from Linux/Delphi 10.2 console application - linux

Question

How can I execute an external program from a Linux console application created in Delphi 10.2 Tokyo?
What I want to do is execute a shell command with parameters like
/home/test/qrencode -o /tmp/abc.png '08154711'
I do not need the output of the program but it should be executed synchronously.
It is easy in Windows environments but as 64 bit Linux support in Delphi (after Kylix) is quite new, I could not find any hints on the Web by now.
Any tip helping me to solve that is very appreciated.
Thanks in advance!

Answer 1

Davids hint pointed me to an example that helped creating the solution. The most tricky part was finding out how to convert a Delphi string to a MarshaledAString as the example used a const string as argument for popen. I tested on RHEL 7.3, runs like a charm.
uses
...
System.SysUtils,
Posix.Base,
Posix.Fcntl,
...;
type
TStreamHandle = pointer;
function popen(const command: MarshaledAString; const _type: MarshaledAString): TStreamHandle; cdecl;
external libc name _PU + 'popen';
function pclose(filehandle: TStreamHandle): int32; cdecl; external libc name _PU + 'pclose';
function fgets(buffer: pointer; size: int32; Stream: TStreamHandle): pointer; cdecl; external libc name _PU + 'fgets';
function runCommand(const acommand: MarshaledAString): String;
// run a linux shell command and return output
// Adapted from http://chapmanworld.com/2017/04/06/calling-linux-commands-from-delphi/
var
handle: TStreamHandle;
data: array [0 .. 511] of uint8;
function bufferToString(buffer: pointer; maxSize: uint32): string;
var
cursor: ^uint8;
endOfBuffer: nativeuint;
begin
if not assigned(buffer) then
exit;
cursor := buffer;
endOfBuffer := nativeuint(cursor) + maxSize;
while (nativeuint(cursor) < endOfBuffer) and (cursor^ <> 0) do
begin
result := result + chr(cursor^);
cursor := pointer(succ(nativeuint(cursor)));
end;
end;
begin
result := '';
handle := popen(acommand, 'r');
try
while fgets(#data[0], sizeof(data), handle) <> nil do
begin
result := result + bufferToString(#data[0], sizeof(data));
end;
finally
pclose(handle);
end;
end;
function createQRCode(id, fn: string): string;
// Create qr-code using qrencode package
begin
deletefile(fn);
if fileExists(fn) then
raise Exception.create('Old file not deleted!');
// I am targeting rhel for now, so I know the path for sure
result := runCommand(MarshaledAString(UTF8STring('/usr/bin/qrencode -o ' + fn + ' ''' + id + '''')));
if not fileExists(fn) then
raise Exception.create('New file not created!');
end;
function testqr: String;
// Test QR Code creation with error handling
// QREncode does not output anything but who knows ;-)
begin
try
result := createQRCode('08154711', '/tmp/myqrcode.png');
except
on e: Exception do
begin
result := 'Error: ' + e.message;
end;
end;
end;

Answer 2

I wrote this code to do this task
uses
System.SysUtils,
System.Classes,
Posix.Base,
Posix.Fcntl;
type
TStreamHandle = pointer;
TLinuxUtils = class
public
class function RunCommandLine(ACommand : string) : TStringList;overload;
class function RunCommandLine(Acommand : string; Return : TProc<String>) : boolean; overload;
class function findParameter(AParameter : string) : boolean;
end;
function popen(const command: MarshaledAString; const _type: MarshaledAString): TStreamHandle; cdecl; external libc name _PU + 'popen';
function pclose(filehandle: TStreamHandle): int32; cdecl; external libc name _PU + 'pclose';
function fgets(buffer: pointer; size: int32; Stream: TStreamHAndle): pointer; cdecl; external libc name _PU + 'fgets';
implementation
class function TLinuxUtils.RunCommandLine(ACommand : string) : TStringList;
var
Handle: TStreamHandle;
Data: array[0..511] of uint8;
M : TMarshaller;
begin
Result := TStringList.Create;
try
Handle := popen(M.AsAnsi(PWideChar(ACommand)).ToPointer,'r');
try
while fgets(#data[0],Sizeof(Data),Handle)<>nil do begin
Result.Add(Copy(UTF8ToString(#Data[0]),1,UTF8ToString(#Data[0]).Length -1));//,sizeof(Data)));
end;
finally
pclose(Handle);
end;
except
on E: Exception do
Result.Add(E.ClassName + ': ' + E.Message);
end;
end;
class function TLinuxUtils.RunCommandLine(Acommand : string; Return : TProc<string>) : boolean;
var
Handle: TStreamHandle;
Data: array[0..511] of uint8;
M : TMarshaller;
begin
Result := false;
try
Handle := popen(M.AsAnsi(PWideChar(ACommand)).ToPointer,'r');
try
while fgets(#data[0],Sizeof(Data),Handle)<>nil do begin
Return(Copy(UTF8ToString(#Data[0]),1,UTF8ToString(#Data[0]).Length -1));//,sizeof(Data)));
end;
finally
pclose(Handle);
end;
except
on E: Exception do
Return(E.ClassName + ': ' + E.Message);
end;
end;
class function TLinuxUtils.findParameter(AParameter : string) : boolean;
var
I : Integer;
begin
Result := false;
for I := 0 to Pred(ParamCount) do
begin
Result := AParameter.ToUpper = ParamStr(i).ToUpper;
if Result then
Break;
end;
end;
You do not have to worry about MarshaledString.
The RunCommandLine function has 2 ways to be called. The first you have the return on a TStringList with all the lines that the console will return.
The second you can pass an anonymous method that will treat line by line of return of the command line.