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Full Discussion: Preserve output order when redirecting stdout and stderr
Top Forums Shell Programming and Scripting Preserve output order when redirecting stdout and stderr Post 302382098 by Boemm on Tuesday 22nd of December 2009 06:26:08 AM
Old 12-22-2009
Preserve output order when redirecting stdout and stderr
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 have some standard script or executable which outputs some messages to stdout and some to stderr.
I try to get write the output to 2 separate files and want the complete output in the order it's printed by the called script to console.

The redirect into 2 files and the additional output to console works with some nice redirections and/or sub shells, but in every case the order of the printed lines are afterwards mixed up ...
If using sub shells, the output is printed more or less randomly, depending on how long each sub shell needs to get executed.
If using redirections, then either all the stdout lines will be printed first and afterwards all the stderr lines or vice versa (depending on which of them are logged first with tee).

I hacked those 2 examples which shows the explained problems.
The first is the one with sub shells, the second the one with redirects:

1:
Code:
./test.sh 2> >(while read l; do echo $l >> stderr.log; echo err: $l; done) 1> >(while read l; do echo $l >> stdout.log; echo out: $l; done)

2:
Code:
(./test.sh 2>&1 1>&3 | tee errors.log) 3>&1 1>&2 | tee output.log

If you try it, you will see, both prints all the output to console and write them to the separate files, but the output is not in the right order some times ...

Can somebody help me out and provide a working solution for this annoying problem!?
I would also be glad about something in perl or some other usual scripting language.

Thanks in advantage!
Steffen
 

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LEARN ABOUT CENTOS

annotate-output

ANNOTATE-OUTPUT(1)					      General Commands Manual						ANNOTATE-OUTPUT(1)

NAME

       annotate-output - annotate program output with time and stream

SYNOPSIS

       annotate-output [options] program [args ...]

DESCRIPTION

       annotate-output will execute the specified program, while prepending every line with the current time and O for stdout and E for stderr.

OPTIONS

       +FORMAT
	      Controls the timestamp format, as per date(1).  Defaults to "%H:%M:%S".

       -h, --help
	      Display a help message and exit successfully.

EXAMPLE

       $ annotate-output make
       21:41:21 I: Started make
       21:41:21 O: gcc -Wall program.c
       21:43:18 E: program.c: Couldn't compile, and took me ages to find out
       21:43:19 E: collect2: ld returned 1 exit status
       21:43:19 E: make: *** [all] Error 1
       21:43:19 I: Finished with exitcode 2

BUGS

       Since  stdout  and  stderr  are	processed  in parallel, it can happen that some lines received on stdout will show up before later-printed
       stderr lines (and vice-versa).

       This is unfortunately very hard to fix with the current annotation strategy.  A fix would involve  switching  to  PTRACE'ing  the  process.
       Giving nice a (much) higher priority over the executed program could however cause this behaviour to show up less frequently.

       The program does not work as well when the output is not linewise.  In particular, when an interactive program asks for input, the question
       might not be shown until after you have answered it.  This will give the impression that the annotated program has hung, while it has not.

SEE ALSO

       date(1)

SUPPORT

       This program is community-supported (meaning: you'll need to fix it yourself).  Patches are however appreciated, as is any feedback  (posi-
       tive or negative).

AUTHOR

       annotate-output	was written by Jeroen van Wolffelaar <jeroen@wolffelaar.nl> This manpage comes under the same copyright as annotate-output
       itself, read /usr/bin/annotate-output (or wherever you install it) for the details.

DEBIAN
								 Debian Utilities						ANNOTATE-OUTPUT(1)
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