I want to disable the buffering of the output stream. curl has the option --no-buffer to disable that buffering.
I am searching for this option in pyCurl but did not find any in documentation. Could you please guide me here?
--no-buffer is for the tool only and is not an option passed to libcurl - it probably has no counter-part in pycurl.
The curl tool implements this option by calling fflush() on the output stream at the end of the write callback. You can most likely implement the same thing in your pycurl-using application.
Related
I need to run this shell command in a C++ script:
"/usr/local/bin/mjpg_streamer -i "/usr/local/lib/input_uvc.so" -o "/usr/local/lib/output_http.so –w /usr/local/www" -b"
This command launches an application which broadcasts a video feed. When I execute this command via system() in C++ the application doesn't start properly.
I use:
system("/usr/local/bin/mjpg_streamer -i \"/usr/local/lib/input_uvc.so\" -o \"/usr/local/lib/output_http.so –w /usr/local/www\" -b");
When I try to access the video stream after I started it with the C++ application the webpage returns:
501: Not Implemented!
no www-folder configured
I can't expect you guys to give me an application related solution, but I'm wondering if there's a difference in the way commands from a C++ application using system() and commands directly entered in a terminal are executed.
EDIT: The application broadcasts the video stream on IP:8080. I access it by going to that IP in my browser. Usually it opens a webpage with the stream in it but when I execute the command with the C++ application I get that error.
Edit: The old idea of mis-placed quotes was wrong; I realize that -w is actually an option to output_http.so, so the whole shebang must be passed as a single parameter to the -o option, as shown here or here etc.
In that case, check file permissions etc. Does /usr/local/www exist? Is it possible that you are running the shell command from a root shell?
Hey, I have a book recommendation, too, "one of the best tech books ever published": Stevens' Advanced Programming in the Unix Environment. The guy knows -- sorry: knew -- what he was talking about.
I would avoid using the system(3) library function, or at the very least, check its returning error code. I don't understand why you are using " inside your command (I believe that in your particular case, you don't need them; but in general beware of code injection!). Read about globbing
You could use popen(3) to at least get the output of the command.
Even better, code yourself the running of the mjpg_streamer program using the fork(2) & execve(2) & waitpid(2) and other syscalls(2) (perhaps pipe(2), poll(2), dup2(2) etc...). Read Advanced Lnux Programming for more.
I want my program to download some audio file from a link I give it and save it.
I know this can be easily done in the command line using curl (for instance: curl -A "Mozilla" "www.example.com" > hello.mp3
I saw examples where system() was used to run curl (i.e it looked something like system(curl -A "Mozilla" "www.example.com" > hello.mp3) . Even though this is an easy solution it seems bad to me.
Would it be better practice to write an equivalent code using the matching library (libcurl in this case)?
What do you guys think?
P.S - This is a general question in a sense. What I mean by that is that there are many command line programs which can be run by system() to get a fast and easy result. The question is if it's okay to use this method to achieve it.
Yes, it would be better to use libcurl directly. That's what it exists for.
That way, you avoid:
the cost of a system call
the cost of spawning a new process
potential security-related bugs in your system call
Invoking curl from the shell will basically just spawn a new shell and new process for no reason, then go ahead and use libcurl inside that process anyway. Cut out the middle man.
I have a program that executes various shell commands via system() and occasionally prints to cout. I want to redirect all output coming from system() calls to a log file so they don't clutter up the normal output. Can I do this without having to append > log to all my system commands?
Looks like you can use popen
Close the stdio file descriptors (0, 1, and 2) and re-open them on whatever output device you like.
Using system is just a bad idea, period. If you use fork and execve or posix_spawn, you can easily make the necessary redirections and avoid all sorts of vulnerabilities from shell quoting issues.
If you can use a library that wrap process call. It is hard to code from posix. I use boost.process, it works fine. you can simply tell the lib how you want the output to be redirected...
my2c
I'm working on a Command Line app to help me on launchd tasks to know if a task is running by returning a BOOL, the problem comes when i need to do a command line and obtain the output for further parsing.
i'm coding it in C/C++ so i can't use NSTask for it, any ideas on how to achieve the goal?
The Command
sudo launchctl list -x [job_label]
If i use system(), i'm unable to get the output so in further research I came with popen(), but no success there.
Thanks in advance.
You'll want to create a pipe from which you can read the output of the program. This will involve using pipe, fork, exec*, and maybe even dup. There's a good tutorial on the linux documentation project.
You can do it the home-brew way with pipe(), fork(), and the exec*() family of functions, or you could use popen() if its constraints meet your requirements.
Writing a program in c++ and I want to issue a system command from the system() function but I don't want the user to see the command (because the command includes a pwd) in the executable window. I need to copy a file from the user's directory onto the server without allowing user access to the server or displaying the pwd. Figured having a .exe that does this is the easiest way.
Ex:
system("FILETRANSFER_SW.exe -pw helloWORLD11!# C:/temp.txt F:/tempfolder/")
But the executable window is showing this command, hence defeating the purpose of trying to hide the password.
I tried issuing
system("#echo OFF")
at the beginning of the program but that does not suppress the following commands, they still show up in the executable window.
Any suggestions?
Thanks...
The command line of running processes is considered public information in most operating systems.
Therefore it is a very bad idea to pass passwords on the command line.
There are two common workarounds to this problem, both of which require the support of the executable being called:
instead of passing the username/password on the command line, pass the name of a file containing the username/password
re-set the command line of the running process from within the called executable.
The first solution is easy and universally possible, the second one has a race condition and is harder to implement, because there's no cross-platform way to do it (on some OSes, changing argv will help).
I'm assuming from your command line that you're using Windows. If it doesn't need to be portable I would suggest you use the CreateProcess() API instead of calling system().
The CreateProcess() API can take a command-line and you can set up the STARTUP_INFORMATION parameter to hide the new process window (wShowWindow = SW_HIDE).
The command line will be hidden from the casual user, but as others have pointed out, it's not that hard to retrieve. Since you are creating a new process, I would suggest writing the sensitive data to that process' standard input. That way the process can just read it and proceed normally.
Using CreateProcess() API will hide the sensitive data from a user, but a power user can easily get the command line associated with the process using a free utilty, e.g. Process Explorer
Another solution is to send the password between your programs, encrypted with something like 3DES, or AES.
You could use a pipe to comunicate between both programs, and don't use the command line at all.
But any of this schemes is not really secure they can be circumvent rather easily. If you want more security you should use some kind of challenge-response protocol with the server.