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Full Discussion: grep sed and a loop
Top Forums UNIX for Dummies Questions & Answers grep sed and a loop Post 302521630 by agama on Thursday 12th of May 2011 12:21:22 AM
Old 05-12-2011
Here is a simple example of how to process a log file and save the last line for reference on the next run. It uses the entire last line from the log as the reference point, rather than a date/time stamp. Less efficient, but more accurate. I'm sure there are other ways to make this more efficient, but this might help get you started.

It does run in Kshell. Should run in bash, but for several reasons I prefer Kshell and didn't test it under bash, so beware if you want to use this as a bash script.

Code:
#!/usr/bin/env ksh


logf=$1                 # log file to suss; supplied as parameter on cmd line
pat=$2                  # pattern to search log for
this=${0##*/}           # base name of script
lastf=/tmp/$this.data   # file where we tuck our last found line away for next time

if [[ -z $logf || -z $pat ]]        # error if logfile name or pattern isn't supplied
then
    echo "usage: $0 log-file-name pattern"
    exit 1
fi

if [[ ! -s $lastf ]]    # no last run data; must check all lines from log
then
    need_all=1          # this will cause us to check for pattern straight away
fi

# parse the log file writing, to stdout, any matches that haven't been seen yet
# The last line seen is written to the last data file for next time.
#
awk  -v snarf=$need_all -v lastf=$lastf -v pat=$pat '
    BEGIN {
        if( !snarf )                # not in check all mode, must find last data
        {
            getline < lastf;
            last_data = $0;
            close( lastf );
        }
    }

    snarf {                         # need all, or found the last line from prev run
        if( match( $0, pat ) )      # if it contains the pattern, print it to stdout
            print;
        new_last = $0;              # save the last line we saw
        next;                       # go to next input line (skip remaining awk code)
    }

    {       # not snarfing yet, check to see if this is the last line we saw before
        snarf = $0 == last_data;    # start snarfing if it matches
        # tricky way of saying:
        # if( $0 == last_data)
        #     snarf = 1;
    }

    END {
        if( new_last )
            printf( "%s\n", new_last) >lastf;   # save our last observed line in the data file.
    }
' <$logf

exit $?           # return the exit code that awk returned with

The one thing this script doesn't do is to deal with the case where the log file has been rolled off. In this case the data file would be non-empty, but we'd need to start checking for the pattern at the start of the log rather than after the previous marker is encountered.

The easy solution to this is to remove the last data file when the log is rolled. If that's not possible, then additional code will be needed to detect this condition; beyond my few minutes to spend answering questions tonight -- sorry.

If you need some info about awk, this is a decent set of doc:
Awk - A Tutorial and Introduction - by Bruce Barnett
and there are other posts on this forum that link other sites.

Hope this helps.
 

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LEARN ABOUT OPENSOLARIS

grablogs.conf

grablogs.conf(4)						   File Formats 						  grablogs.conf(4)

NAME

       grablogs.conf - grablogs configuration for libgrablogs.so of the plugins of
	gnome-system-log file

SYNOPSIS

       /usr/lib/gnome-system-log/plugins/grablogs.conf

DESCRIPTION

       The  libgrablogs.so  is	a plugin for gnome-system-log(1), it colloct the log files from the system as many as possible. grablogs.conf is a
       configuration file that contains a set of lines mixed with sh(1) syntax codes and individual
	log files. libgrablogs.so will read the file try to get a log files list for
	gnome-system-log(1). Users can copy the file into $HOME/.gnome2/gnome-system-log/plugins/`uname -p` to overwrite the system default one.

       The grablogs.conf file contains the following configuration categories:

	      [configs]
		     Each line under this category is interpreted as a config file of System. The plugin will open the config file and try to find
		     all system paths of the logs.

	      [commands]
		     Each line under this category is interpreted as a shell command and will be execute through a pipe. And each line of the out-
		     put of the command will be interpreted as a log path.

	      [logs] Each line under this category is interpreted as a log path.

FILES

       /usr/lib/gnome-system-log/plugins/grablogs.conf
	      The system default configuration file for the plugin libgrablogs.so

       $HOME/.gnome2/gnome-system-log/plugins/`uname -p`/grablogs.conf
	      The user specific configuration file for the plugin libgrablogs.so

EMAMPLE

       [configs]
       /etc/syslog.conf
       [commands]
       for i in `svcs -aH -o FMRI | grep -v lrc `; do svcprop -p restarter/logfile $i  2>/dev/null  ||	svcprop  -q  -p  restarter/alt_logfile	$i
       2>/dev/null ; done
       [logs]
       /var/log/messages
       /var/log/secure
       /var/log/maillog
       /var/log/cron
       /var/log/Xorg.0.log
       /var/log/XFree86.0.log
       /var/log/auth.log
       /var/log/cups/error_log

SEE ALSO

       gnome-system-log(1), pipelog.conf(1)

gnome-utils 2.16.0						    13 Oct 2006 						  grablogs.conf(4)
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