I've seen valid uses of cat on a single file before, but this is the first valid use I've seen for no files. Interesting. This is, of course, assuming that these programs output lines atomically, but still.
I hadn't realized that files wouldn't necessarily be atomic, for that matter.
So from now on we can say "alister told us so" when we are using useless use of cat
No seriously, in my suggestion I was thinking either STDOUT or STDERR, and that was wrong (was testing with a simple command not a script). Now when I'm testing with a script that has output I see that output to STDOUT is overwriting some characters in STDERR in the resulting "logfile".
But in your suggestion, I don't understand what is happening, see comments:
The blame for that behavior almost certainly lies with your ls implementation. Which ls are you using?
I can reproduce that behavior with GNU ls. I cannot reproduce it with busybox ls. A closer look using strace (I booted a Linux system just for this ) confirmed my suspicions: GNU ls isn't even trying to write a line at a time.
This is how GNU ls and Busybox ls attempt to write an error message for a nonexistent file named idont:
There is no way to fix or workaround that, short of fixing GNU ls (or whatever code it depends on for generating its error messages). Perhaps other ls implementations (and other utilities for that matter) suffer from that problem, but there's nothing that can be done about this at the shell level.
With that many writes for a single, relatively short error message, there's a good chance that another process will be given the chance to write to the shared pipe. Each write is still atomic, it's just the message that's broken.
Regards,
Alister
---------- Post updated at 04:31 PM ---------- Previous update was at 04:26 PM ----------
Quote:
Originally Posted by 244an
You need to save stdout at the time that it's pointing to the cat-pipe because, later, when the shell builds the script|tee pipeline and redirect's script's stdout to the tee-pipe, if not for fd 3, there would be no way to refer to the cat-pipe (which script needs so that its stdout can bypass tee).
Regards,
Alister
Last edited by alister; 09-07-2012 at 05:38 PM..
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The blame for that behavior almost certainly lies with your ls implementation. Which ls are you using?
I can reproduce that behavior with GNU ls.
Yep, alister, my ls is ls (GNU coreutils) 8.5.
Just for the sake of curiosity, I was wondering whether we could try an ugly workaround (I know it's at least ugly): if GNU ls splits too much its error messages, what about a little pause between ls and tee?
It seems to work. Here below the count of "nonefile"s gives us the number of
broken logs:
so 56 broken logs out of 1000 tries, versus:
0 broken out of 100 tries.
BTW: of course, if one doesn't care at all about having all the errors at the beginning or at the end of the log, a solution is obvious:
Dear all,
redirecting STDOUT & STDERR to file is quite simple, I'm currently using:
Code:
exec 1>>/tmp/tmp.log; exec 2>>/tmp/tmp.log
But during script execution I would like the output come back again to screen, how to do that?
Thanks
Luc
edit by bakunin: please use CODE-tags like the... (6 Replies)
Hi folks
I need/want to redirect output (stdout, stderr) from an exec call to separate files. One for stderr only and two(!) different (!) ones for the combined output of stderr and stdout.
After some research and testing i got this so far :
(( exec ${command} ${command_parameters} 3>&1... (6 Replies)
Dear all,
redirecting STDOUT & STDERR to file is quite simple, I'm currently using:
exec 1>>/tmp/tmp.log; exec 2>>/tmp/tmp.logBut during script execution I would like the output come back again to screen, how to do that?
Thanks
Lucas (4 Replies)
I originally wrote my script using the korn shell and had to port it to bash on a another server. My script is working find for backing up but noticed that now after the move, I am not getting any output to my log files.
Using Korn shell, this worked for me for some odd reason. This was sending... (2 Replies)
Hi,
I already searched through the forum and tried to find a answer for my problem but I didn't found a full working solution, thats way I start this new thread and hope, some can help out.
I wonder that I'm not able to find a working solution for the following scenario:
Working in bash I... (8 Replies)
Hi
I am not if this is possible: is it possible in bach (or another shell) to redirect GLOBALLY the stdout/stderr channels to a file.
So, if I have a script
script.sh
cmd1
cmd2
cmd3
I want all stdout/stderr goes to a file. I know I can do:
./script.sh 1>file 2>&1
OR
... (2 Replies)
working on a c sell script
I think I understand the concept of it, which is:
filename >> file.txt (to appaend)
or filename | tee -a file.txt (to append)
The problem is that my shell script is used with several parameters, and these commands don't seem to work with just filename. They... (2 Replies)
Hi friends
I am facing one problem while redirecting the out of the stderr and stdout to a file
let example my problem with a simple example
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ps -ef &
ls &
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Friends
I have to redirect STDERR messages both to screen and also capture the same in a file.
2 > &1 | tee file works but it also displays the non error messages to file, while i only need error messages.
Can anyone help?? (10 Replies)
In bash, I need to send the STDOUT and STDERR from a command to one file, and then just STDERR to another file. Doing one or the other using redirects is easy, but trying to do both at once is a bit tricky. Anyone have any ideas? (9 Replies)