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Full Discussion: Bash statement equivalent
Top Forums UNIX for Dummies Questions & Answers Bash statement equivalent Post 302921358 by Corona688 on Thursday 16th of October 2014 02:47:45 PM
Old 10-16-2014
I'm not sure this ever did quite what you thought. It could certainly change the perceived order of stdout/stderr. The two different, separate tees are liable to stomp on each other's lines. And this may interfere with redirections run outside the script, too. It's only a strange concidence of how bash works that gives this the appearance of working under some circumstances, but it also did weird things like catching prompts...

Potentially changing the order stdout/stderr come in order is inevitable when doing this, and doing this reliably is always cumbersome since it's supposed to be done from the outside.

This is the shortest "reliable" one I've yet seen managed:

Code:
#!/bin/ksh

log=ksh.log

rm -f $log /tmp/$$-e /tmp/$$-o /tmp/$$-m
mkfifo /tmp/$$-o /tmp/$$-e /tmp/$$-m || exit 1

(       tee /tmp/$$-m /dev/tty < /tmp/$$-o & # will wait for exec >
        tee /tmp/$$-m /dev/tty < /tmp/$$-e & # will wait for exec 2>
        cat < /tmp/$$-m > $log &             # will wait for $$-m
        ) >/dev/null

exec > /tmp/$$-o        # First tee will start running
exec 2>/tmp/$$-e        # Second tee will start running
while [ ! -e "$log" ] ; do true ; done
rm -f /tmp/$$-o /tmp/$$-e /tmp/$$-m

echo "stdout stuff"
echo "stderr stuff">&2

There's shorter/simpler versions using tail -f, to just print the output file instead of catching it midway, but it's possible for them to skip output and hang, not to mention all your output ends up going to stdout. The worst this one will do is reorder stderr/stdout and possibly print a line on your prompt after it quits -- unfortunately inevitable unless you're prepared to make a lot of guarantees about what your code will and won't be doing with traps and stdin/stdout/stderr. Right now this shouldn't interfere with those.
Last edited by Corona688; 10-16-2014 at 03:56 PM..
 

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LEARN ABOUT SUNOS

chroot

chroot(1M)						  System Administration Commands						chroot(1M)

NAME

       chroot - change root directory for a command

SYNOPSIS

       /usr/sbin/chroot newroot command

DESCRIPTION

       The  chroot  utility causes command to be executed relative to newroot. The meaning of any initial slashes (/) in the path names is changed
       to newroot for command and any of its child processes. Upon execution, the initial working directory is newroot.

       Notice that redirecting the output of command to a file,

       chroot newroot command >x

       will create the file x relative to the original root of command, not the new one.

       The new root path name is always relative to the current root. Even if a chroot is currently in effect, the newroot argument is relative to
       the current root of the running process.

       This command can be run only by the super-user.

RETURN VALUES

       The exit status of chroot is the return value of command.

EXAMPLES

       Example 1: Using the chroot Utility

       The  chroot  utility  provides an easy way to extract tar files (see tar(1)) written with absolute filenames to a different location. It is
       necessary to copy the shared libraries used by tar (see ldd(1)) to the newroot filesystem.

       example# mkdir /tmp/lib; cd /lib
       example# cp ld.so.1 libc.so.1 libcmd.so.1 libdl.so.1 libsec.so.1 /tmp/lib
       example# cp /usr/bin/tar /tmp
       example# dd if=/dev/rmt/0 | chroot /tmp tar xvf -

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       cd(1), tar(1), chroot(2), ttyname(3C), attributes(5)

NOTES

       Exercise extreme caution when referencing device files in the new root file system.

       References by routines such as ttyname(3C) to stdin, stdout, and stderr will find that the device associated with the  file  descriptor	is
       unknown after chroot is run.

SunOS 5.10							    15 Dec 2003 							chroot(1M)
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