Bash copy stderr file

For more information on the various control and redirection operators, see here. First thing to note is that there's couple of ways depending on your purpose and shell, therefore this requires slight understanding of multiple aspects.

Additionally, certain commands such as time and strace write output to stderr by default, and may or may not provide a method of redirection specific to that command. Basic theory behind redirection is that a process spawned by shell assuming it is an external command and not shell built-in is created via fork and execve syscalls, and before that happens another syscall dup2 performs necessary redirects before execve happens. In that sense, redirections are inherited from the parent shell.

In case of csh and its derivatives, the stderr redirection doesn't quite work there. Note, that the integer or redirection operator cannot be quoted, otherwise shell doesn't recognize them as such, and instead treats as literal string of text. As for spacing, it's important that integer is right next to redirection operator, but file can either be next to redirection operator or not, i.

The trick here is that redirection can appear anywhere. For scripts, we can redirect stderr stream of the whole script from outside as in myscript. The exec built-in has the power to rewire the stream for the whole shell session, so to speak, whether interactively or via script. Something like. Yet another way is via functions. As kopciuszek noted in his answer, we can write function declaration with already attached redirection, that is.

Commands such as time and strace write their output to stderr by default. Active 4 years, 5 months ago. Viewed 30k times. Improve this question. Ghillie Dhu 1 1 silver badge 9 9 bronze badges. There is a highly upvoted answer to a similar question on StackOverflow which answers this question quite thoroughly.

Add a comment. Active Oldest Votes. You are looking for tee. See man tee for details. Improve this answer. I have looked at it. Maybe I am not using the right syntax? I have writen about tee in combination with process substitution.

Linux identifies each file objects with file descriptor A non-negative integer that represents the open files in the session. Linux has given us two file descriptors or channels to distinguish the Output and the Error so that we can redirect them to two different locations or files as per our requirement.

Now having this basic understanding. If you look at the preceding command you can see that we are trying to list two files at the same time. Amongst them, one is not present. As said earlier, By Default both stdout and stderr would be displayed in the stdout channel only. In the previous command, we just redirected the stderr into the file and displayed the standard output on the terminal.

But If we want to redirect the stdout and stderr to two different files at the same time. In the preceding command, you can notice we are using the same strategy of prefixing the file descriptor numeric value of stdout and stderr with the redirection symbols followed by the appropriate file names. Hope it helped you to understand the stdout and stderr and how to use them. We all know that the bash echo command prints everything that you give after that.

In fact, echo command does not even return any error or nonzero return code. Consider the following script with two echo messages. We are going to apply the same trick of file descriptors and redirection symbol. Asked 11 years, 6 months ago.

Active 3 years, 8 months ago. Viewed 12k times. Is that possible? Improve this question. Cristiano Paris Cristiano Paris 1, 2 2 gold badges 14 14 silver badges 20 20 bronze badges. See How can I send stdout to multiple commands? Add a comment. Active Oldest Votes.

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