Bash statement equivalent Post: 302921358

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Top Forums UNIX for Dummies Questions & Answers Bash statement equivalent Post 302921358 by Corona688 on Thursday 16th of October 2014 02:47:45 PM

10-16-2014

Registered User

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 SUSE

rbash

RBASH(1)						      General Commands Manual							  RBASH(1)

NAME

       rbash - restricted bash, see bash(1)

RESTRICTED SHELL

       If  bash  is  started with the name rbash, or the -r option is supplied at invocation, the shell becomes restricted.  A restricted shell is
       used to set up an environment more controlled than the standard shell.  It behaves identically to bash with the exception that the  follow-
       ing are disallowed or not performed:

       o      changing directories with cd

       o      setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV

       o      specifying command names containing /

       o      specifying a filename containing a / as an argument to the .  builtin command

       o      specifying a filename containing a slash as an argument to the -p option to the hash builtin command

       o      importing function definitions from the shell environment at startup

       o      parsing the value of SHELLOPTS from the shell environment at startup

       o      redirecting output using the >, >|, <>, >&, &>, and >> redirection operators

       o      using the exec builtin command to replace the shell with another command

       o      adding or deleting builtin commands with the -f and -d options to the enable builtin command

       o      using the enable builtin command to enable disabled shell builtins

       o      specifying the -p option to the command builtin command

       o      turning off restricted mode with set +r or set +o restricted.

       These restrictions are enforced after any startup files are read.

       When a command that is found to be a shell script is executed, rbash turns off any restrictions in the shell spawned to execute the script.

SEE ALSO

       bash(1)

GNU Bash-4.0							    2004 Apr 20 							  RBASH(1)

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