Calling, executing, and passing argument to external programs from a
GUI
lazarus / 32-Linux

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Gizmo · 2011-08-03 21:47

Hi

I am coding a GUI to help automate decryption of a particular
encryption system (eCryptfs).

There is a Linux command called ecryptfs-unwrap-passphrase that
resides in /usr/bin/. When it's ran, it asks the user for their login
password, a bit like when you try and do something using sudo or when
you try to su.

I am trying to call this program from mine. I have read
http://www.freepascal.org/docs-html/fcl/process/tprocess.html and
followed
http://wiki.lazarus.freepascal.org/Executing_External_Programs.

Before I continue trying to make this work, I have two questions :

1) Can you call a none graphical command line program from within a
GUI like I am trying to do? Though my program compiles, it hangs, and
I can't work out if that because the answer to this question is "no,
you can't", or if it's due to question 2

2) How do you call a program and also pass that program additional
values? i.e. Assuming the answer to 1 above is "yes", and the reason
my program is hanging is merely because ecryptfs-unwrap-passphrase is
waiting for the user to input a password but it can't be displayed on
screen, how do I pass both the command and the password that I want it
to use? e.g. ecryptfs-unwrap-passphrase MyPassword

So far I have :

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject); var  FileToAttack : String; 
UnwrapPassphraseProcess: TProcess;  UnwrapPassphraseOutput:
TStringList; begin  if OpenDialog1.Execute then    begin   
FileToAttack := OpenDialog1.FileName;    if FileExists(FileToAttack)
then       begin       Edit1.Caption := FileToAttack;     
 UnwrapPassphraseProcess := TProcess.Create(nil);     
 UnwrapPassphraseOutput.Create;      
 UnwrapPassphraseProcess.CommandLine := ('/usr/bin/ecryptfs-unwrap-
passphrase ');        // Have also tried ..:= ('/usr/bin/ecryptfs-
unwrap-passphrase ' + 'MyPassword')     
 UnwrapPassphraseProcess.Options := UnwrapPassphraseProcess.Options +
[poWaitOnExit, poUsePipes];       UnwrapPassphraseProcess.Execute;   
  UnwrapPassphraseOutput.LoadFromStream(UnwrapPassphraseProcess.Output
);       UnwrapPassphraseOutput.SaveToFile('/home/ted/testing.txt');  
     UnwrapPassphraseProcess.Free;       UnwrapPassphraseOutput.Free; 
     OpenDialog1.Close;       end     else        ShowMessage('An
error occurred opening the passphrase file.');    end;end;           
                            
Thanks

Ted

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Leledumbo · 2011-08-03 22:50

Quote1) Can you call a none graphical command line program from within
a GUI like I am trying to do? Yes, if not, we won't have many GUI
wrappers created with Lazarus.
Quote2) How do you call a program and also pass that program
additional values? i.e. Assuming the answer to 1 above is "yes", and
the reason my program is hanging is merely because ecryptfs-unwrap-
passphrase is waiting for the user to input a password but it can't be
displayed on screen, how do I pass both the command and the password
that I want it to use? e.g. ecryptfs-unwrap-passphrase
MyPasswordExploit the Input and Output (and probably StdErr)
properties of TProcess. Use Input to write to the process (as if you
type something with the keyboard) and Output for reading what the
program outputs. Don't forget that some (or most?) programs requires
EOLn to be sent before they process the given input. Try the attached
example for concrete code.

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Gizmo · 2011-08-04 10:32

That is very useful...thanks! And thanks for taking the time to attach
the example. I had read about the Input and Output properties of
TProcess shortly before posting this but I couldn't work out exactly
how it worked. Your example has clarified that so I will try again
tonight when I get home.

Ted