Stdout file file number

When you redirect any command output to a file, you will notice that the error messages are printed on the terminal window. A numeric file descriptor is used to represent each stream.

In this post, we will grasp the information that comes under redirecting stdout and stderr to file. Each operating system based on Linux has a conviction of a default place for the executed command. Your Bash or Zsh shell is constantly looking for the default output location. When the shell detects new output, it displays it on the terminal screen for you to see it.

Otherwise, it will send the output to its default location. It is already available to your program from the beginning together with stdin and stderr. What they point to or from can be anything, actually the stream just provides your program an object that can be used as an interface to send or retrieve data. By default it is usually the terminal but it can be redirected wherever you want: a file, to a pipe goint to another process and so on. K Scott Piel wrote a great answer here , but I want to add one important point.

Read more here: Why does printf not flush after the call unless a newline is in the format string? Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. What does it mean to write to stdout in C? Ask Question. Asked 8 years, 8 months ago.

Active 1 year, 7 months ago. Viewed k times. Improve this question. Acroyear Acroyear 1, 3 3 gold badges 20 20 silver badges 36 36 bronze badges. There are different ways an error may occur. For this example, sending ls an invalid argument will result in an error.

This is a common technique that takes full advantage of the stdin and stdout streams. Here, the sign is responsible for piping. The output echo generates is written in the stdout stream. Then, the piping redirects the content of stdout to stdin for the grep command. Piping is a form of redirection.

However, it only involves stdin and stdout. Bash allows specific control over all three of the streams. If the file did already exists, then the command above will overwrite it. Find centralized, trusted content and collaborate around the technologies you use most.

Connect and share knowledge within a single location that is structured and easy to search. After some searching work, I draw the following conclusion. Could you help me review it and correct any mistake in it? In unistd. The stdout locates in a higher level user level? You might use it for write syscall. Except after you do weird things like fclose stdout ; , or perhaps some freopen after some fclose stdin , which you should almost never do! See this , as commented by J. Sometimes, you may want to call fflush to flush buffers.

You could use file descriptor numbers for syscalls like write 2 which is used by the stdio library , or poll 2. But using syscalls is clumpsy.