How To Redirect Output To Dev Null In C
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I have a command I am running produces a ton of output, I want to silence the output without writing to a file. I have used the following to send all output to a file, but again I don't want any file output: command out.txt 2&1 I have used command /dev/null on my CentOS box before, but I. I also use the /dev/null redirection to suppress an output from SQLPLUS to the stdout. But now I want to execute another SQLPLUS statement (in the same script file) and I need to send that new output to STDOUT so it could be displayed to the user.
‘m a new Linux system user. How can I redirect command error output /dev/null on a Linux or Unix-like system using Bash shell?Your shell comes with three file descriptors as follows:
Jun 05, 2014 What is a null (/dev/null) file in a Linux or Unix-like systems? /dev/null is nothing but a special file that discards all data written to it. The length of the null device is always zero. In this example, first, send output of date command to the screen and later to the /dev/null i.e. Discards date command output.
- Input and output redirection in the C shell. Before the C shell executes a command, it scans the command line for redirection characters. Note that the default standard input for a command run detached is not changed to the empty /dev/null file. Instead, the standard input remains the original standard input of the shell.
- Sending data into the void with /dev/null. It easy to make output that you don't want to see simply disappear. NUL and you'll get the same effect as you would redirecting data to /dev/null.
- Jun 05, 2014 What is a null (/dev/null) file in a Linux or Unix-like systems? /dev/null is nothing but a special file that discards all data written to it. The length of the null device is always zero. In this example, first, send output of date command to the screen and later to the /dev/null i.e. Discards date command output.
- stdin – 0 – Standard Input (usually keyboard or file)
- stdout – 1 – Standard Output (usually screen)
- stderr – 2 – Standard Error (usually screen)
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What is a null (/dev/null) file in a Linux or Unix-like systems?
/dev/null is nothing but a special file that discards all data written to it. The length of the null device is always zero. In this example, first, send output of date command to the screen and later to the /dev/null i.e. discards date command output:
Syntax: Standard Error (stderr -2 no) to a file or /dev/null
The syntax is as follows:
In this example, send output of find command to /dev/null:$ find /etc -type f -name '*' 2>/dev/null
The following example will cause the stderr ouput of a program to be written to a file called errors.txt:$ find /etc/ -type f -name '*' 2> errors.txt
Linux and Unix redirect all output and error to file
The syntax is:
If you want both stderr and stdout in same file, try:
How To Redirect Output To Dev Null In C 1
Use cat command to display log.txt on screen:cat log.txt
How To Redirect Output To Dev Null In C Pdf
See man pages for more information – ksh(1).
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Basically, you're ripping the floor out from under your program without guaranteeing that the Right Thing has happened to put a new floor back. The 'stdout' file pointer will continue to work, but anything not informed of the change might not -- like cout, and any subprocesses you happen to run. Their output may not go where you expected, or go nowhere at all, or crash. It might work right, if the next file opened happens to land at file descriptor 1 -- or it might not. The behavior is undefined and at the mercy of what libraries and compiler you're using. All that's guaranteed after you do that is that stdio routines like printf() will go where you redirected.
Whatever file descriptor 1 went to before, might not be properly closed after freopen, either. If stdout was an open file descriptor to a terminal preventing your ssh window from closing, such is life.
The 'right thing' to do if you really want to redirect 'standard output', not just the stdio external variable 'stdout', is to ensure that the file you want is opened specifically as file descriptor one, which is what dup2() does in the example you were given. Which is much simpler than it looks once you realize it's redirecting twice: Once for stdout, once for stderr. Re-opening onto file descriptor one with dup2() also guarantees that whatever was there before, is forced to close. This could be especially important if that happened to be a terminal or device file.
Also, your example is concerning. Never mix printf and cout, for starters, especially if you're going to play funny games with redirection.