how can a bash script which is in a pipe detect that it's data source has died.? - bash

Question

I am working on a horribly old machine without logrorate.
[ Actually it has busybox 0.6, which is 'void of form' for most purposes. ]
I have openvpn running and I'd like to be able to see what it's been up to. The openvpn I'm using can output progress info to stdout or to a named log file.
I tried and failed to find a way to stop it using one log file and start it on another. Maybe some SIGUSR or something will make it close and re-open the output file, but I can't find it.
So I wrote a script which reads from stdin, and directs output to a rotating log file.
So now all I need to do is pipe the output from openvpn to it.
Job done.
Except that if I kill openvpn, the script which is processing its output just runs forever. There's nothing more it can do, so I'd like it to die automatically.
Is there any way to trap the situation in the script "EOF on STDIN" or something using "find the process ID which is feeding my stdin", or whatever?
I see that this resembles the question
"Tee does not exit after pipeline it's on has finished"
but it's not quite that in that I have no control over the behaviour of openvpn ( save that I can kill it ). I do have control over the script that receives the output of openvpn, but can't work out how to detect the death of openvpn, or the pipe from it to me.
My upper-level script is roughly:
vpn_command="openvpn --writepid ${sole_vpn_pid_file} \
--config /etc/openvpn/openvpn.conf \
--remote ${VPN_HOST} ${VPN_PORT} "
# collapse sequences of multiple spaces to one space
vpn_command_tight=$(echo -e ${vpn_command}) # must not quote the parameter
# We pass the pid file over explicitly in case we ever want to use multiple VPNs.
( ./${launchAndWaitScriptFullName} "${vpn_command_tight}" "${sole_vpn_pid_file}" 2>&1 | \
./vpn-log-rotate.sh 10000 /var/log/openvpn/openvpn.log ) &
if I kill the openvpn process, the "vpn-log-rotate.sh" one stays running.
that is:
#!/bin/sh
# #file vpn-log-rotate.sh
#
# #brief rotates stdin out to 2 levels of log files
#
# #param linesPerFile Number of lines to be placed in each log file.
# #param logFile Name of the primary log file.
#
# Archives the last log files on entry to .last files, then starts clean.
#
# #FIXME DGC 28-Nov-2014
# Note that this script does not die if the previous stage of the pipeline dies.
# It is possible that use of "trap SIGPIPE" or similar might fix that.
#
# #copyright Copyright Dexdyne Ltd 2014. All rights reserved.
#
# #author DGC
linesPerFile="$1"
logFile="$2"
# The location of this script as an absolute path. ( e.g. /home/Scripts )
scriptHomePathAndDirName="$(dirname "$(readlink -f $0)")"
# The name of this script
scriptName="$( basename $0 )"
. ${scriptHomePathAndDirName}/vpn-common.inc.sh
# Includes /sbin/script_start.inc.sh
# Reads config file
# Sets up vpn_temp_directory
# Sets up functions to obtain process id, and check if process is running.
# includes vpn-script-macros
# Remember our PID, to make it easier for a supervisor script to locate and kill us.
echo $$ > ${vpn_log_rotate_pid_file}
onExit()
{
echo "vpn-log-rotate.sh is exiting now"
rm -f ${vpn_log_rotate_pid_file}
}
trap "( onExit )" EXIT
logFileRotate1="${logFile}.1"
# Currently remember the 2 previous logs, in a rather knife-and-fork manner.
logFileMinus1="${logfile}.minus1"
logFileMinus2="${logfile}.minus2"
logFileRotate1Minus1="${logFileRotate1}.minus1"
logFileRotate1Minus2="${logFileRotate1}.minus2"
# The primary log file exist, rename it to be the rotated version.
rotateLogs()
{
if [ -f "${logFile}" ]
then
mv -f "${logFile}" "${logFileRotate1}"
fi
}
# The log files exist, rename them to be the archived copies.
archiveLogs()
{
if [ -f "${logFileMinus1}" ]
then
mv -f "${logFileMinus1}" "${logFileMinus2}"
fi
if [ -f "${logFile}" ]
then
mv -f "${logFile}" "${logFileMinus1}"
fi
if [ -f "${logFileRotate1Minus1}" ]
then
mv -f "${logFileRotate1Minus1}" "${logFileRotate1Minus2}"
fi
if [ -f "${logFileRotate1}" ]
then
mv -f "${logFileRotate1}" "${logFileRotate1Minus1}"
fi
}
archiveLogs
rm -f "${LogFile}"
rm -f "${logFileRotate1}"
while true
do
lines=0
while [ ${lines} -lt ${linesPerFile} ]
do
read line
lines=$(( ${lines} + 1 ))
#echo $lines
echo ${line} >> ${logFile}
done
mv -f "${logFile}" "${logFileRotate1}"
done
exit_0

Answer 1

Change this:
read line
to this:
read line || exit
so that if read-ing fails (because you've reached EOF), you exit.
Better yet, change it to this:
IFS= read -r line || exit
so that you don't discard leading whitespace, and don't treat backslashes as special.
And while you're at it, be sure to change this:
echo ${line} >> ${logFile}
to this:
printf %s "$line" >> "$logFile"
so that you don't run into problems if $line has a leading -, or contains * or ?, or whatnot.