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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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SCRIPT(1)							   User Commands							 SCRIPT(1)

NAME
script - make typescript of terminal session SYNOPSIS
script [options] [file] DESCRIPTION
script makes a typescript of everything displayed on your terminal. It is useful for students who need a hardcopy record of an interactive session as proof of an assignment, as the typescript file can be printed out later with lpr(1). If the argument file is given, script saves the dialogue in this file. If no filename is given, the dialogue is saved in the file type- script. OPTIONS
-a, --append Append the output to file or to typescript, retaining the prior contents. -c, --command command Run the command rather than an interactive shell. This makes it easy for a script to capture the output of a program that behaves differently when its stdout is not a tty. -e, --return Return the exit code of the child process. Uses the same format as bash termination on signal termination exit code is 128+n. -f, --flush Flush output after each write. This is nice for telecooperation: one person does `mkfifo foo; script -f foo', and another can supervise real-time what is being done using `cat foo'. --force Allow the default output destination, i.e. the typescript file, to be a hard or symbolic link. The command will follow a symbolic link. -q, --quiet Be quiet (do not write start and done messages to standard output). -t[file], --timing[=file] Output timing data to standard error, or to file when given. This data contains two fields, separated by a space. The first field indicates how much time elapsed since the previous output. The second field indicates how many characters were output this time. This information can be used to replay typescripts with realistic typing and output delays. -V, --version Display version information and exit. -h, --help Display help text and exit. NOTES
The script ends when the forked shell exits (a control-D for the Bourne shell (sh(1)), and exit, logout or control-d (if ignoreeof is not set) for the C-shell, csh(1)). Certain interactive commands, such as vi(1), create garbage in the typescript file. script works best with commands that do not manipulate the screen, the results are meant to emulate a hardcopy terminal. It is not recommended to run script in non-interactive shells. The inner shell of script is always interactive, and this could lead to unexpected results. If you use script in the shell initialization file, you have to avoid entering an infinite loop. You can use for example the .profile file, which is read by login shells only: if test -t 0 ; then script exit fi You should also avoid use of script in command pipes, as script can read more input than you would expect. ENVIRONMENT
The following environment variable is utilized by script: SHELL If the variable SHELL exists, the shell forked by script will be that shell. If SHELL is not set, the Bourne shell is assumed. (Most shells set this variable automatically). SEE ALSO
csh(1) (for the history mechanism), scriptreplay(1) HISTORY
The script command appeared in 3.0BSD. BUGS
script places everything in the log file, including linefeeds and backspaces. This is not what the naive user expects. script is primarily designed for interactive terminal sessions. When stdin is not a terminal (for example: echo foo | script), then the session can hang, because the interactive shell within the script session misses EOF and script has no clue when to close the session. See the NOTES section for more information. AVAILABILITY
The script command is part of the util-linux package and is available from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils /util-linux/>. util-linux June 2014 SCRIPT(1)
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