I have application that has to write to console. Also I call function from dll that writes to stdout too. Now I want to have separate output window to get all output from dll there. (So I will have 2 console windows: one for client app, one for dll) How to make it? I use windows+mingw
You can't. stdout is a single file handle and if both your application code and the dll are writing to it, they're going to go to the same place no matter what you do.
Your best options would be to either:
change your application code to write to something besides stdout (i.e stderr or a file), or
change your application code so that its output statements are 'tagged' in a way that you can filter using a tool like grep or sed/awk
Related
I know how to get the stdout into a file using dup/dup2 system calls, but how do I get the entire output that would be normally shown on my terminal(including the prompt that says my username along with the $ symbol and the current working directory) to a file?
Yes you can, but this may be difficult in many details (depending on your expert level). For the shell to behave normally (I would mean exactly as in a terminal), then it needs to interact with a terminal (special system object). So you need to create a program that behave like a terminal, this what pseudo-terminals devices (/dev) are intended for. Read documentation about this to implement it but roughly, your application should behave like the user so should be connected to the slave side of the pseudo-terminal, and the shell to the master side of the pseudo-terminal. Then you can easily log real inputs made by the user and catch outputs made by the shell.
Can't comment cause of low reputation.
I would say there is no way to do that inside a code in C. Instead, you could use bash for example to redirect everything to a file, and leave the code in C as it is.
In this way you have all the info you want to save: prompt, current directory, call to the program (including flags), and of course the output of the program.
Well, you can do:
-For bash prompt PS1: Echo expanded PS1 (in case you want it expanded, if not there is a simple way to do it just echong PS1)
- For executed command: https://unix.stackexchange.com/questions/169259/how-to-capture-command-line-input-into-logfile-and-execute-it-at-the-same-time
- Standard output and error output: Redirect stderr and stdout in a Bash script
And that's all you want to capture, I think.
Look up the script command in Unix systems. If you want to capture all keyboard and std in/out for a command, use the script executable. If you want to see how it's done, look up the source.
I am writing a program in C that is started simply by the terminal. Now I want to make the program itself open another terminal with a custom size and write its output in there.
I found the command
system("gnome-terminal");
which opens another terminal, but I can't find a function that lets me write into this second terminal. I am using Ubuntu.
If you have any idea, that would be great
The easiest thing would probably be to write the output to a file, say /tmp/tmp96888 (tip: mkstemp) and then do something like
system("gnome-terminal --geometry=40x14 --command 'less /tmp/tmp96888'");
Or, to update continuously from the file:
system("gnome-terminal --geometry=40x14 --command 'tail -f /tmp/tmp96888'");
But if you can, I think the best way is to open a new terminal and run the program itself in it, and just print the output. It's only if you actually need to do things in the original window that you have to bother with a separate output window.
I'm calling a C executable compiled using Cygwin in MATLAB, using the unix() function. This works fine, and I can see the desired output on the MATLAB command window. However, there is an fprintf() inside the executable that is supposed to create and write to a text file which does not run - no such file is created. The text file is created just fine when I run the executable directly through Cygwin.
I was wondering if I need to grant permissions to the MATLAB file/executable to enable this? How could I go about this?
What path are you using to create the file? It might have been created -- just not where you expected it.
If it's a relative path, you could use getcwd(2) inside your C program to get and print the working directory (or e.g. getpid(2) to get the PID and then do ls -d /proc/<pid>/cwd, which will work on Linux at least). Once you have the working directory, check if the file is somewhere in there.
If it looks like the file really isn't being created, my next step would be to add some error checking to functions and print messages for errors to try to figure out what's going on. strerror(3) and perror(3) might come in handy.
My situation is the following: I've got a lot of small gizmos ( pretty close to routers, not exactly but anyway that's irrelevant) ; they are running a bare-bones MIPS-based Linux distro.
To control them, one can telnet there ( thru serial port ) and issue commands to an interactive bash-like shell which then writes back some output. The shell's input and output are both attached to /dev/ttyAS0.
Now, I'd like to automate all of this, i.e. write a program that will run inside the gizmo, be a small server listening on some port, and which would pass on any command to the said shell, capture shell's output and relay it back to whoever contacted to server.
I:
1) can install (small, <500KB) programs inside the gizmo
2) can't modify the OS, startup scripts, the shell, anything
3) have root access
4) know how to write a SOAP server
5) know how to get a SOAP message, translate it to a command and inject it into /dev/ttyAS0
6) DONT KNOW how to capture the shell's reply
7) know how to, having shell's reply, translate it back to a SOAP message and reply to the original inquirer.
So basically, the problem is 6) : how to, having injected a string to /dev/ttyAS0 and thus having made the shell execute it, capture the shell's output ?
I am aware of
http://etbe.coker.com.au/2008/02/27/redirecting-output-from-a-running-process/
i.e. I know that I could change the shell's stdout if I had GDB ( or strace ) running inside the box, but I can't install it there - it's too big and anyway this approach seems too much like a hack.
So, summarizing:
How root can capture stdout of an already running process, IN PURE C, without gdb or strace, with no access to the way the process is started?
Or - almost equivalently - how to capture what's being written to a terminal, IN PURE C ?
You might want to take a look at reptyr. It will probably need some adaptation to work for your system though
Have you tried driving the serial port with a kermit script? I would probably forgo trying to insert a more clever proxy on the device and just try and drive the existing interface.
If you really want to get it on the device, you may be able to look at the source to something like screen or kermit to get a sense of how they interact with ttys.
Suppose I create a thread from my "main" thread, which aims to monitor and print some variables in "main". But "main" is also generating some output, so I want to print the outputs of these two threads separately. How can I redirect the output of the new thread to a new console other than the one "main" thread is using in my c program?
I would output the monitoring information to a file, then use tail -f filename to display it in my other terminal.
That has the advantage that you can run grep or what-have-you on the output as well.
I would go with writing the data to a log file and then using tail -f log_file.txt from another window to watch it since that way you get to keep a copy of the data, but if you decide that you need to use separate terminals then you can just open the new terminal (tty) like a regular file. The main problem with this is that you probably really want it to open a new terminal window for you as well.
Opening a new terminal window to do something like this is tricky and is different between different terminal emulators. Here is another question about opening new terminals from a make file. You could try doing the same thing from your program or from a script that runs your program and run cat or tail in the new terminal to be your log window.
#!/bin/sh
truncate --size=0 ./logfile.txt
xterm "tail -f ./logfile.txt" 2>&1 > /dev/null &
your_program --log-file=./logfile.txt
I don't currently know of a better way to accomplish this.
Another thing you might want to look into is syslog.
What would you expect to happen in such case (externally)?
If you run a program you are attached to a console. You of course don't have to write output to the console (you can use files), but the console cannot be duplicated obviously.
Isn't using a different file descriptor good enough for you?