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Luke Cousins Luke Cousins 6 6 bronze badges. Add a comment. Active Oldest Votes. Improve this answer. Ok, thanks. I can still do this but will the pid be correct, or that of tee etc? Active Oldest Votes. Improve this answer. So hashdeep -rXvvl -j 30 -k checksums. Faria yes. But the last two commands are equivalent, they will send both error and output to the same file. Show 7 more comments. 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.
Something like! Sergiy Kolodyazhnyy Sergiy Kolodyazhnyy The Overflow Blog. Podcast Making Agile work for data science. Stack Gives Back Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually. Linked Changing file descriptor 1 doesn't affect file descriptor 3 from now on.
Now, file descriptors 3 and 4 point to standard output and standard error respectively. These will be used as real terminal standard output and standard error.
At the same time it copies the same input to file descriptor 3 the terminal the second part, very similar, is about doing the same trick for standard error and file descriptors 2 and 4.
That's true although it depends on intentions. My approach is to always create a unique and timestamped log file. The other is to append. Both ways are 'logrotateable'. I prefer separate files which require less parsing but as I said, whatever makes your boat floating : — quizac. Your second solution is informative, but what's with all the cleanup code? It doesn't seem relevant, and if so, only muddles an otherwise good example. I like it better with the cleanup code.
It might be a bit of distraction from the core example, but stripping it would make the example incomplete. The net is already full of examples without error handling, or at least a friendly note that it still needs about a hundred lines of code to make is safe to use.
I wanted to elaborate on clean-up code. So, once the main process dies they become inherited by init[1]. They will not become zombies defunc. The clean-up code makes sure that all background tasks are killed, if main script dies. It also applies to any other process which might have been created and running in background.
Mark Mark. Finally, I'd note that there is a simpler way to do this: From section 3. One generates output and the other does not! Evan Rosica Evan Rosica 1, 11 11 silver badges 20 20 bronze badges.
File descriptors 0, 1, 2 are just offsets into a table. I use the term dup because that is the system call that is used to duplicate the file descriptor. This is actually very important, and less known. Good call. Connect and share knowledge within a single location that is structured and easy to search. Is there any way I can output the stderr to the error file and output stdout to the output file in the same line of bash?
The numerals 0 through 9 are file descriptors in bash. Multiple commands' output can be redirected. This works for either the command line or most usefully in a bash script. The -s directs the password prompt to the screen. 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. How to redirect stderr and stdout to different files in the same line in script? Ask Question.
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