How to compare previous and current item in for loop in bash?

Shell Programming and Scripting
1

Hey,
I am trying to compare formated login and logout dates from one user at a host which I have stored in a tmp directory in order to find out the total login time. I need to compare them in order to find overlapping intervals.

At first I tried to store each log in and logo date in an array but it doesn't work. Can anyone help me?

2

Give example data which you have tried to parse.

3 
loginn()
for logu in $(ls /tmp/$lognam/wtmp*)
do
logina=$(echo $(last -f $logu -F $name) | cut -c40-63)
    for loga in $logina
    do loginn[$i]=$(echo "$(date +"%s" -d"$loga" 2>/dev/null)")
    i=$(($i+1))
    done
done
4

Here is example to calculate diff between login and session time ... easy to modify ..
using ksh93

#!/usr/bin/ksh
prev=""
name="someuser"

for logu in /tmp/$lognam/wtmp*
do
  last -f "$logu" -F "$name"
done  | while read line
do
 flds=($line)
        loginstart="${flds[4]} ${flds[5]} ${flds[6]} ${flds[7]}"
        loginend="${flds[10]} ${flds[11]} ${flds[12]} ${flds[13]}"
        [ "$loginstart" = "" ] && continue
        [ "$prev" = "" ] && prev="$loginstart" && continue
        epocnow=$(printf "%(%#)T" "$loginstart")
        epoclogout=$(printf "%(%#)T" "$loginend")
        epocprev=$(printf "%(%#)T" "$prev")
        ((logintime=epoclogout - epocnow))
        ((diff=epocprev-epocnow))
        ((h=diff/3600))
        ((s1=diff-3600*h))
        ((m=s1/60))
        ((s=s1-m*60 ))
        echo "$diff|$logintime|$prev|$loginstart|$h:$m:$s"
        prev="$loginstart"
done