elapsed time between two log records

bash_calc_elapsed_time_log_record.sh

#!/bin/bash

#
# parses the time (in seconds) that elapsed between 2 consecutive entries
# each matching to pattern1 and pattern2.
# date format : [DDD] [MMM] [dd] [hh]:[mm]:[ss] [YYYY]
# example     : Tue May 12 06:49:44 2009
#
# substitute the patterns at will
#
# limitation : it works for entries having the same year
#
# example
# Tue May 12 06:49:41 2009 - pattern1
# Tue May 12 06:49:44 2009 - pattern2
#
# it should output :
# 3
#

awk '
BEGIN{
        m["Jan"]="01";
        m["Feb"]="02";
        m["Mar"]="03";
        m["Apr"]="04";
        m["May"]="05";
        m["Jun"]="06";
        m["Jul"]="07";
        m["Aug"]="08";
        m["Sep"]="09";
        m["Oct"]="10";
        m["Nov"]="11";
        m["Dec"]="12";

        d["Sun"]="01";
        d["Mon"]="02";
        d["Tue"]="03";
        d["Wed"]="04";
        d["Thu"]="05";
        d["Fri"]="06";
        d["Sat"]="07";

        s=0; # start timestamp
        e=0; # end timestamp
}
/pattern1/ {    dt1=$0; gsub(":"," ",$4);
                spec1=sprintf("%s %s %s %s",$5,d[$1],m[$2],$4);
                s=mktime(spec1); }
/pattern2/ {
                dt2=$0; gsub(":"," ",$4);
                spec2=sprintf("%s %s %s %s",$5,d[$1],m[$2],$4);
                e=mktime(spec2); print e-s; e=s=0; }' < $1