How do I get my script to monitor a new file using tail?

Shell Programming and Scripting
1

Hi,

I have a script which basically watches a log file for new lines using tail, then takes action based on what is logged. I wrote a script to do this for me and its working great, my only problem is that once per week, this log file is archived to another directory, and a new log is created. I need to monitor the NEW log file, but even though the old one is moved, my tail which is always running (tail -f | while) still seems to be looking at the OLD file. How can I get my script to work and start reading the NEW log file each week? The only way I can think of to do this is to have another script which runs every week that kills my script and re-starts it...

Here is the specific line in my script where it stops and sits forever when the log file is archived (ASAI.log) and a new one is created:
tail -n1 -f /home/dirTalk/current_dir/oamlog/ASAI.log | while read output_line

Here is the entire script:

#!/usr/bin/ksh
#############################################################################
# Created by Jeff Civitano on 5/27/2009 for Armonk
#############################################################################
CheckforLock()
{
    # See if an instance of setmwiq_remove is already running by looking for setmwiq_remove_lockfile
    cat /home/dtuser/bin/setmwiq_remove_lockfile > /dev/null 2>&1
    if (test $? -eq 0) then
        #setmwiq_remove already running
        return 1
    fi
    if (test $? -ne 0) then
        #setmwiq_remove not running
        return 0
    fi
}
CreateLock()
{
    # Create setmwiq_remove_lockfile
    touch /home/dtuser/bin/setmwiq_remove_lockfile
    echo "setmwiq_remove created setmwiq_remove_lockfile " >> /home/dirTalk/current_dir/oamlog/setmwiq_remove.log
}
DeleteLock()
{
    # Delete setmwiq_remove_lockfile
    rm /home/dtuser/bin/setmwiq_remove_lockfile
    echo "setmwiq_remove deleted setmwiq_remove_lockfile" >> /home/dirTalk/current_dir/oamlog/setmwiq_remove.log
}
# MAIN
# Is the script already running?
CheckforLock  #Invoke the function
CheckforLockrc=$?
if (test $CheckforLockrc -eq 1) then
    exit 0
fi
# script is not running, create lock
CreateLock
date >> /home/dirTalk/current_dir/oamlog/setmwiq_remove.log
db2 "connect to dtdbv220" >> /home/dirTalk/current_dir/oamlog/setmwiq_remove.log
last_profile=0
switch=3
# Get latest profile number from ASAI.log to Remove from setmwiq
tail -n1 -f /home/dirTalk/current_dir/oamlog/ASAI.log | while read output_line 
do
echo $output_line | grep "confirmed for" > /home/dtuser/bin/profile_file
wc -l /home/dtuser/bin/profile_file | awk '{print $1}' | read count
if ((count>0)) then
    cat /home/dtuser/bin/profile_file | awk '{print $8}' | read profile
    cat /home/dtuser/bin/profile_file | awk '{print $5}' | read OnOrOff
    rc=`echo $profile | grep $last_profile | wc -l | awk '{print $1}'`
    if (test $rc -eq 0) then
      if [[ $OnOrOff = "on" ]]; then
        switch=1
      fi
      if [[ $OnOrOff = "off" ]]; then
        switch=0
      fi
      echo "MWI confirmed for [$profile], remove from setmwiq table:" >> /home/dirTalk/current_dir/oamlog/setmwiq_remove.log
      echo "db2 delete from setmwiq where user_id='$profile' and switch=$switch" >> /home/dirTalk/current_dir/oamlog/setmwiq_remove.log
      db2 "delete from setmwiq where user_id='$profile' and switch=$switch" >> /home/dirTalk/current_dir/oamlog/setmwiq_remove.log
      last_profile=$profile
    fi
fi
done
date >> /home/dirTalk/current_dir/oamlog/setmwiq_remove.log
db2 "quit" >> /home/dirTalk/current_dir/oamlog/setmwiq_remove.log
rm /home/dtuser/bin/profile_file
# script finished, delete lock
DeleteLock
2

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3

Disclaimer: I use bash, not ksh

use -F or --retry. So:

tail -n1 -f --retry /home/dirTalk/current_dir/oamlog/ASAI.log | while read output_line

 or

tail -n1 -F /home/dirTalk/current_dir/oamlog/ASAI.log | while read output_line

MG

4

-F or --retry doesn't seem to work on my system (AIX 5.3):
$>tail -n1 -F IMC_Stats.log
Usage: tail [-f] [-c Number|-n Number|-m Number|-b Number|-k Number] [File]
Usage: tail [-r] [-n Number] [File]
Usage: tail [+|-[Number]][l|b|c|k|m][f] [File]

$>tail -n1 --retry IMC_Stats.log
Usage: tail [-f] [-c Number|-n Number|-m Number|-b Number|-k Number] [File]
Usage: tail [-r] [-n Number] [File]
Usage: tail [+|-[Number]][l|b|c|k|m][f] [File]

Any other ideas are appreciated...

5

If you delete the log file you also break the file handle linked with the tail command. Instead of delete the file empty it after archiving with:

cp /dev/null /home/dirTalk/current_dir/oamlog/ASAI.log

Regards