I'm testing this on a basic Hello World C++ application.
Since I can see the std output only if running the application from terminal, I would like to let the application open its terminal by itself (when started by double clicking it), then execute the rest of the code on it.
I've already tried:
system("gnome-terminal");
just at the beginning of main() function.
The terminal opens but nothing gets displayed. I guess it's because it is opened on another thread... ?
So is there another way?
Two problems:
You didn't create any method to communicate with the terminal. If you need bidirectional communication, you could create two pipes, one to go from your program to the terminal and one to go from the terminal to your program.
The way you called system causes your program to wait for gnome-terminal to exit. You need to put an & on the end. In practice, you probably don't want to use system. You'll need to hook the pipes up in-between the fork and the exec, so you shouldn't use system in the first place. Then you can just not wait.
If you want to be ugly, you can use the /proc/self/fd/X mechanism. For example, in theory this could work:
system("gnome-terminal < /proc/self/fd/%d > /proc/self/fd/%d &",
terminal_fd_in, terminal_fd_out);
Just make sure the descriptors are not set to close on exec.
Related
I'm developing an interactive program that takes inputs from the user (through stdin) and outputs data accordingly (using stdout). While the program is running I need to open a background application (and leave it running while the main program is running). I have successfully done this using popen (using the "r" mode), however at times I get stdin conflicts. For example when the user enters an input intended for the main program, sometimes, the program treats it as an input to the background program. The user should never have to interact directly with the background program. Is there a way to completely decouple both the input and the output of the background program from stdin and stdout, while still being able to read and write using a file descriptor to the background process?
Just code exactly what you need. The popen function is a convenience function that you can use what it happens to do exactly what you happen to need. Otherwise, use pipe, fork, dup2, close, and whatever exec-family function you want.
You may find it helpful to look at a few implementations of popen/pclose to see how they work. Adjust as needed.
Simply don't use popen. Instead, use fork + one of the exec family of functions, which doesn't connect the io streams.
I have to write a program that intercepts data from terminal and i have to parse it. After processing when the data, i have to parse it before it goes to stdout.
I can't use tee or commands like prog > file 2>&1 as the program is going to be interactive.
For example :
If the user types ls in the terminal i have to parse it then it should go operating system and then when I get the result after processing I ll have to again parse it before it's displayed in the terminal.
I did my research and I think I can achieve it through pseudo terminal interfaces ( pty ).
Please let me know if there is a better way to achieve it.
I am using cpp and bash and the platform is *nix.
Update:
I can also use libexpect from expect.
I am not sure what do you mean here - you mean interactive program as "working in another terminal communicating with user" or even displaying GUI?
How does it specify the terminal? It is probably important what is program layout here (which program starts which).
If your application uses GUI to communicate with user, then I would simply do it this way:
start bash with sdtin and stdout attached to pipes,
your program reads & writes to it's end's of those pipes, parses data, and reads/writes on it's own stdin&stdout - so it appears on it's terminal.
If you mean controlling different terminal than your application's, it gets though since system generally does not expect program operating on multiple terminals. I don't think it's possible to filter communication between terminal and already working application attached to it. Starting another process spawning another terminal might be an option - to have basically two terminals working in sync. But then you will have to synchronize both processes by some other means (named pipes, network connection or some other IPC).
If you provide more detail on your program I might provide more directed help.
PS Don't tell me that you are writing some terminal keylogger ')
EDIT:
Your program is probably GUI based then - what i would recommend would be something similar to answer linked by banuj.
Best option will probably be to create three pipes, then fork, and in child process assign corresponding ends of pipes to stdin, stdout and stderr. Then child process should exec into shell - probably bash, although I am not sure if other shells would sound better if read out loud ;) Main process will be able to read/write other ends of mentioned pipes, parsing both inputs and outputs to bash and programs it runs.
You could also exec directly to commands user specifies, but that forces you to take over tedious job of a shell - managing current directory, environment variables, job control and so on.
Using above method might however cause some trouble - some programs (usually in security related contexts - eg. su(do) asking for password) will try to bypass stdin/stdout anyway and read directly from terminal device. I am not sure what can you do in such case - programing your own terminal emulator would be an option, but I don't know if you want to go this deep into system programming for this.
If you want some code snippet's, if you don't know how to do above, just ask ;)
I know the system() function but that creates it's own environment so every variable set here isn't forwarded to main console. I wonder is it possible to send command as it would be written by the user or as it would be executed by *.bat file ?
The reason I need this is that I look for a way to set env variable of parent CMD process. And yes I know that system doesn't want me to do it, but maybe there is a some workaround for that...
Idea is to create app that would set as a variable anything that is send to it via input pipe, like this:
echo Bob| setvar name
so then:
echo %name%
would produce Bob
The whole idea is to make easier setting a variable from any program output (I know how to do it with for command) with taking account of peculiarities with special batch characters like ^!% since these are allowed in file names. It would make simpler many cmd scripts.
You can certainly run programs in the same console window as your program. That's the default behavior for CreateProcess. MSDN has more details on what happens between related processes sharing a console. You'll probably want to wait for the child process to terminate before continuing to run your own program.
However, that won't help with your real goal. The window where a program runs has absolutely nothing to do with the environment variables of any of its ancestor processes. You'll have to look elsewhere for a solution to your real problem.
I've got a program called pgm1 which create a new process using fork.
Then in this process, I launch a new program (pgm2) using the following command:
execv( exec_path_name, argv ).
But the thing is that with this method I've got both output in the same terminal.
I've been searching for a while ans the only solution i found was this one:
Open a new terminal with a system call
Attach my pgm2 to the new terminal using this soft http://blog.nelhage.com/2011/01/reptyr-attach-a-running-process-to-a-new-terminal/comment-page-1/#comment-27264
So my question is really simple, is there a more simple way to do that ?
Thanks in advance !
PS: Distro - Ubuntu 11.10 32bit
I can think of two possible solutions:
Do The Right Thing(TM) and send your output to a file: Each process can use a different file, providing both clear separation of the output and better record-keeping. As a bonus, you are also bound to see a performance improvement - terminal output is computationally expensive, even nowadays...
Execute a terminal emulator with the proper arguments: Most terminal emulators provide a way to execute a specific program in place of the shell. For example xterm:
$ xterm top
This will launch top in an xterm instance, without a shell. Quiting top also terminates the xterm window.
If your terminal emulator of choice supports this, you can use it simply by modifying the arguments passed to execv(). Of course, in this case you will be actually executing the terminal emulator instead of your program, which will then call your own process.
Keep in mind that, depending on the terminal emulator, any open file descriptors may not be passed correctly to your program - the terminal will at least mangle the standard file descriptors.
I have a project that I thought was going to be relatively easy, but is turning out to be more of a pain that I had hoped. First, most of the code I'm interacting with is legacy code that I don't have control over, so I can't do big paradigm changes.
Here's a simplified explanation of what I need to do: Say I have a large number of simple programs that read from stdin and write to stdout. (These I can't touch). Basically, input to stdin is a command like "Set temperature to 100" or something like that. And the output is an event "Temperature has been set to 100" or "Temperature has fallen below setpoint".
What I'd like to do is write an application that can start a bunch of these simple programs, watch for events and then send commands to them as necessary. My initial plan was to something like popen, but I need a bidrectional popen to get both read and write pipes. I hacked something together that I call popen2 where I pass it the command to run and two FILE* that get filled with the read and write stream. Then all I need to do is write a simple loop that reads from each of the stdouts from each of the processes, does the logic that it needs and then writes commands back to the proper process.
Here's some pseudocode
FILE *p1read, *p1write;
FILE *p2read, *p2write;
FILE *p3read, *p3write;
//start each command, attach to stdin and stdout
popen2("process1",&p1read,&p1write);
popen2("process2",&p2read,&p2write);
popen2("process3",&p3read,&p3write);
while (1)
{
//read status from each process
char status1[1024];
char status2[1024];
char status3[1024];
fread(status1,1024,p1read);
fread(status2,1024,p2read);
fread(status3,1024,p3read);
char command1[1024];
char command2[1024];
char command3[1024];
//do some logic here
//write command back to each process
fwrite(command1,p1write);
fwrite(command2,p2write);
fwrite(command3,p3write);
}
The real program is more complicated where it peeks in the stream to see if anything is waiting, if not, it will skip that process, likewise if it doesn't need to send a command to a certain process it doesn't. But this code gives the basic idea.
Now this works great on my UNIX box and even pretty good on a Windows XP box with cygwin. However, now I need to get it to work on Win32 natively.
The hard part is that my popen2 uses fork() and execl() to start the process and assign the streams to stdin and stdout of the child processes. Is there a clean way I can do this in windows? Basically, I'd like to create a popen2 that works in windows the same way as my unix version. This way the only windows specific code would be in that function and I could get away with everything else working the same way.
Any Ideas?
Thanks!
On Windows, you invoke CreatePipe first (similar to pipe(2)), then CreateProcess. The trick here is that CreateProcess has a parameter where you can pass stdin, stdout, stderr of the newly-created process.
Notice that when you use stdio, you need to do fdopen to create the file object afterwards, which expects file numbers. In the Microsoft CRT, file numbers are different from OS file handles. So to return the other end of CreatePipe to the caller, you first need _open_osfhandle to get a CRT file number, and then fdopen on that.
If you want to see working code, check out _PyPopen in
http://svn.python.org/view/python/trunk/Modules/posixmodule.c?view=markup
I think you've made a very good start to your problem by using the popen2() function to abstract away the cross-platform issues. I was expecting to come and suggest 'sockets', but I'm sure that's not relevant after reading the question. You could use sockets instead of pipes - it would be hidden in the popen2() function.
I am 99% sure you can implement the required functionality on Windows, using Windows APIs. What I cannot do is point you to the right functions reliably. However, you should be aware the Microsoft has most of the POSIX-like API calls available, but the name is prefixed with '_'. There are also native API calls that achieve the effects of fork and exec.
Your comments suggest that you are aware of issues with availability of data and possible deadlocks - be cautious.