Is this it? NAME popen, pclose – process I/O SYNOPSIS #include <stdio.h> FILE *popen(const char *command, const char *type); int pclose(FILE *stream); DESCRIPTION The popen() function opens a process by creating a pipe, forking, and invoking the shell. Since a pipe is by definition unidirectional, the type argument may specify only reading or writing, not … Read more
All components of a pipeline (if more than one) are executed in a subshell, and their variable assignments do not persist to the main shell. The reason for this is that bash does not support real multithreading (with concurrent access to variables), only subprocesses which run in parallel. How to avoid this: You have to … Read more
This does virtually no error checking, but why so complicated? int main (int argc, char ** argv) { int i; for( i=1; i<argc-1; i++) { int pd[2]; pipe(pd); if (!fork()) { dup2(pd[1], 1); // remap output back to parent execlp(argv[i], argv[i], NULL); perror(“exec”); abort(); } // remap output from previous child to input dup2(pd[0], 0); … Read more
You might think you could do something like the following, but it won’t work. (nmake & call set myError=%%errorlevel%%) | tee output.txt The problem lies in the mechanism by which Windows pipes work. Each side of the pipe is executed in it’s own CMD shell. So any environment variable you set there will disappear once … Read more
Took a bunch of fiddling but I figured it out using the FFmpeg rawvideo demuxer: python capture.py | ffmpeg -f rawvideo -pixel_format bgr24 -video_size 640×480 -framerate 30 -i – foo.avi Since there is no header in raw video specifying the assumed video parameters, the user must specify them in order to be able to decode … Read more
system(): runs command and returns command’s exit status backticks: runs command and returns the command’s output pipes : runs command and allows you to use them as an handle Also backticks redirects the executed program’s STDOUT to a variable, and system sends it to your main program’s STDOUT.
If you want to redirect the output of one program into the input of another, just use a simple pipeline: program1 arg arg | program2 arg arg If you want to save the output of program1 into a file and pipe it into program2, you can use tee(1): program1 arg arg | tee output-file | … Read more
Use a subprocess.PIPE, as explained in the subprocess docs section “Replacing shell pipeline”: import subprocess p1 = subprocess.Popen([“cat”, “file.log”], stdout=subprocess.PIPE) p2 = subprocess.Popen([“tail”, “-1”], stdin=p1.stdout, stdout=subprocess.PIPE) p1.stdout.close() # Allow p1 to receive a SIGPIPE if p2 exits. output,err = p2.communicate() Or, using the sh module, piping becomes composition of functions: import sh output = sh.tail(sh.cat(‘file.log’), … Read more
Without async/await, it’s quite nasty. With async/await, just do this: Promise.all(promises).then(async (responses) => { for (…) { await new Promise(fulfill => stream.on(“finish”, fulfill)); //extract the text out of the PDF } })