C exec redirect output. txt Below is the code I wrote, bu.

C exec redirect output. Seems like there isn't an option of any exec() variants to have an argument to choose where it gets directed to. May 18, 2012 · How to redirect the output of a system call to inside the program in C/C++? Asked 15 years, 5 months ago Modified 11 months ago Viewed 20k times Sep 2, 2019 · Learn the basics of the Linux exec command. Each stream has a buffer, which temporarily stores data to make input/output faster. Aug 30, 2020 · Sometimes, you want to redirect the output of your program to a file–maybe to record it for another program, or because you want to search through it with grep. txt"), but choosing a secure temporary file is a pain. to a file. I'm not sure how to execute a command and have its output write into the pipe. h header). That's part of what confuses me. Unlike temporary redirections (> or >>), exec applies redirection to all subsequent commands within the script. txt Below is the code I wrote, bu Dec 10, 2013 · You cannot perform redirection in this way. How to use exec command for process replacement, redirection and file descriptor manipulation. So the program should be executed like this, I mean this is how I execute it in shell and it works: /opt/prog < in. Jun 14, 2025 · Any C function or Linux command called inside a C program and designed to write to STDOUT should now output to that file. seems like I need to somehow change the normal stderr, stdin, stdout file descriptors to something Oct 9, 2025 · In C++, input and output are performed using streams, which are sequences of bytes, Common stream objects are cin ( reads input from the keyboard) , cout : (displays output on the screen) . log \;"). Nov 17, 2015 · Child reorganizes things so that file descriptor 1 (standard output) goes to the file. While dealing with redirecting output to a file you may use freopen (). If you want to continue using it, you can redirect it's output to a temporary file, by system ("ls > tempfile. I need to run it for multiple files and generate a different output file for each input file and I was wondering how to use find -exec for that. Critically, we achieve this duplication and redirection without any modification to the function code. S This exec construct is usually used in scripts that run in a subshell, to redirect their output e. I don't see a use for it in an interactive session. Executing a command and getting just the exit status is easy using std::system, but also getting output is a bit harder and OS specific. Assuming you are trying to redirect your stdout to a file ' output. I'm having an issue, I cant work out how to get the command output and store it. Mar 12, 2025 · This article demonstrates how to use file redirection in C programming. Usually, you can leave standard error alone; you might redirect standard input from /dev/null. Nov 26, 2014 · I'm trying to write a C program that grabs command output and then i'll be passing that to another program. On Windows I'm using _popen, so the code should be cross platform, except for Aug 25, 2014 · I tried using exec 1>&- but it didn’t work as this closes the STDOUT file descriptor. Jun 25, 2012 · The other answers are valid but, since you asked about a way to redirect the system() output without the use of > operator in terminal, I would recommend using the FILE *freopen(const char *filename, const char *mode, FILE *stream) function (that is part of the stdio. Dec 15, 2011 · Don't use pipe when the output is to go to a file. Or, you can even redirect it through another program: system ("ls | otherprogram"); Some may recommend the popen () command. . When you fork the child to run the ls command, you note the redirection, and open the file; you then use dup2() (or close() and dup()) so that the file descriptor is now standard output for the child; you close the duplicated file descriptor - the one returned by open(); then you execute ls as usual; its standard output is now sent to the file Nov 6, 2006 · Hi guys, I am writing a shell in C and it is going well. This is what you want if you can process the output Jul 6, 2021 · Recently I had to parse some command line output inside a C++ program. For example, sending cout output to Jul 22, 2025 · Explore methods to execute external commands from C++, capture their standard output and error, and manage return codes effectively. With practical code examples and explanations, you'll gain valuable insights into managing files in your applications. txt ' then you can write- Mar 18, 2016 · Want to redirect stdin to file in execve (). I am trying Feb 11, 2015 · Use of the exec builtin for input/output redirection is specified by the POSIX definition for the Shell Command Language, and the exec builtin is available in any POSIX compatible shell. I have one script that only writes data to stdout. By using popen, a POSIX C function we can get both the exit status as well as the output of a given command. I am now up to additing redirection into the shell but have run into some dramas. If you want to redirect stdout for a process you're about to exec, you need to open the path and dup2 it onto the appropriate file descriptor. If you're executing more complex commands, you may need to put braces around the whole command sequence. Before the C shell executes a command, it scans the command line for redirection characters. If you have to do this at the C level, there are a few ways you can accomplish this. Jul 23, 2025 · The exec command in Linux allows you to permanently redirect standard output (stdout) and standard error (stderr) for an entire script or session. Please throw light on this entire operation of exec 1>file and exec 1>&- What will happen if we close the standard file descriptors 0, 1, 2 by using exec 0>&- exec 1>&- exec 2>&-? Feb 25, 2009 · I want to reopen the stdin and stdout (and perhaps stderr while I'm at it) filehandles, so that future calls to printf() or putchar() or puts() will go to a file, and future calls to getc() and suc Hi folks, I would like to redirect the stdout and stderr of a child process to a grpc server side stream. I/O redirection means changing where the program gets input from or sends output to. Learn to redirect input and output streams effectively using C's standard I/O functions. The main problem is in the pipe_exec() function below. Explore the Linux exec command and its practical applications, including understanding the exec system call, executing external commands, and redirecting input/output. Nov 17, 2015 · Child reorganizes things so that file descriptor 1 (standard output) goes to the file. Example: Oct 3, 2017 · The first suggests that redirect just doesn't work inside exec ("A shell command can include redirection and piping; -exec cannot (although the whole find can be redirected)"), the second says it works anywhere inside or out ("set the output inside the exec " and "-exec ls {} >> /tmp/test. g. If you're executing a simple command, just include the redirection in the command line. These special notations direct the shell to redirect input and output. I've been doing some quick search and only found c'ish way of doing these. v63 agqk4 rnco zz5mi4 zptw zgv0ew y3yq wvs cdic hfe6