[Wylug-help] Bash Scripting question.

[Frank Shute]

On Wed, Feb 26, 2003 at 03:28:31AM -0700, Thomas, Nicholas wrote:
>
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>
> Hi,
>
> I have a bash script to write and it would be nice if it had the following
> attributes:
>
> 1) A simple script which throws out text messages to the console when
> running in the foreground, using the echo command.
> Whilst simultaneously sending the same output to a log file.
>
> 2) The script can be sent to the background (Using Ctrl-Z then 'bg' ). The
> log file still gets its message text, but the console no longer
> gets any messages. The script continues to run in the background.
>
> 3) I can resume foreground operation, using 'fg', and the console messages
> start coming out on the console again. I am not worried about losing
> the console messages which were generated while the script was in the
> background because I can review the log file for the complete list.
>
> I presume this is possible?
>
> Kind Regards
>
> Nick Thomas
> --

Following up on my earlier post suggesting trapping signals, I wrote
this small demo. I use BSD sh but the principles (& syntax) are much the
same for bash by the looks of things:

<----------------->

#!/bin/sh

# Grab functions
# Use source builtin for bash

. ~/shellfuncs/myfuncs

#
# Those functions:
#
#
# setlog () {
# 	while true; do
# 	sleep 5
# 	echo "Hello logfile!" >> ~/logfile
# 	done
# 	}
#
# setcon () {
# 	while true; do
# 	sleep 5
# 	echo "Hello console & logfile!" | tee -a ~/logfile
# 	done
# 	}


trap setcon USR1
trap setlog USR2

# Set up a loop...

while true; do
	sleep 5
	setcon
done

trap - USR1 USR2		# reset signal handlers

<----------------->

Then:

$ ./demosig &
[2] 20618
Hello console & logfile!
Hello console & logfile!
Hello console & logfile!
..

$ kill -USR2 20618

$ tail -f ~/logfile
Hello console & logfile!
Hello console & logfile!
Hello console & logfile!
Hello logfile!
Hello logfile!
^C

$ kill -USR1 20618
Hello console & logfile!
Hello console & logfile!
Hello console & logfile!
..

Isn't it easier to just use tail? ;)

You might also want to have a look at GNU screen.

BTW, kill & tee might be a bit different on Linux - can't remember.

I also cheated a bit and used a couple of xterms rather than vc's.
(The program output gets in the way of interacting with the shell).

--

 Frank

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