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Full Discussion: How to compare previous and current item in for loop in bash?
Top Forums Shell Programming and Scripting How to compare previous and current item in for loop in bash? Post 302988617 by kshji on Thursday 29th of December 2016 02:05:31 PM
Old 12-29-2016
Here is example to calculate diff between login and session time ... easy to modify ..
using ksh93
Code:
#!/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

 

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LEARN ABOUT CENTOS

prev

PREV(1) 							     [nmh-1.5]								   PREV(1)

NAME

       prev - show the previous message

SYNOPSIS

       prev [+folder] [-showproc program] [-showmimeproc program] [-header | -noheader] [-checkmime | -nocheckmime] [switches for showproc or
	    showmimeproc] [-version] [-help]

DESCRIPTION

       Prev performs a show on the previous message in the specified (or current) folder.  Like show, it passes any switches  on  to  the  program
       named by showproc or showmimeproc, which is called to list the message.	This command is almost exactly equivalent to "show prev".  Consult
       the manual entry for show(1) for all the details.

FILES

       $HOME/.mh_profile	  The user profile

PROFILE COMPONENTS

       Path:		    To determine the user's nmh directory
       Current-Folder:	    To find the default current folder
       showproc:	    Program to show non-MIME messages
       showmimeproc:	    Program to show MIME messages

SEE ALSO

       show(1), next(1)

DEFAULTS

       `+folder' defaults to the current folder
       `-checkmime'
       `-header'

CONTEXT

       If a folder is specified, it will become the current folder.  The message that is shown (i.e.,  the  previous  message  in  sequence)  will
       become the current message.

BUGS

       prev  is  really  a link to the show program.  As a result, if you make a link to prev and that link is not called prev, your link will act
       like show instead.  To circumvent this, add a profile-entry for the link to your nmh profile and add the argument prev to the entry.

MH.6.8								   11 June 2012 							   PREV(1)
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