Shell Programming and Scripting

$ LANG=C who -s
gssjgu:/g/g00k00/gssjgu/TMP> LANG=C who -s
gssjgu      pts/1       Jul  4 15:06    (1.1.1.11)  
getk00      pts/2       Jul  4 08:54    (1.1.1.2)   
gti001      pts/3       Jun 22 15:38    (1.1.1.39)  
$

$ cat log5.sh
#!/usr/bin/ksh

typeset -i SINCE=${1:-5}

#
# Get current date
#

date '+%Y +%m %d %H %M' | read year month day hour min

#
# Compute timestamp for current date minus $SINCE minutes 
# format 'mmddHHMM' ('cal' command usage)
#

(( min  -= SINCE ))
(( min  <  0 )) && { (( min += 60 )) ; (( hour -= 1 )) }
(( hour <  0 )) && { (( hour += 24 )) ; (( day -= 1 )) }
(( day  <=  0 )) && { 
   (( month -= 1 ))
   (( month <= 0 )) && { (( month=12 )) ; (( year -= 1 )) }
   day=$(cal $month $year | tr '\n' ' ' | awk '{print $NF}')
}

ts5=$(printf "%02d%02d%02d%02d" $month $day $hour $min)   
#
# Determine users logged on since $SINCE minutes
# (Based on 'who -s' command)'
#

LANG=C who -s |
awk -v ts5="$ts5" -F '[ \t:]*' '
   function to_timestamp(month, day, hour, min) {
      m = index("___,jan,feb,mar,apr,may,jun,jul,aug,sep,oct,nov,dec,", "," tolower(month) ",")/4;
      return sprintf("%02d%02d%02d%02d", m, day, hour, min);
   }
   to_timestamp($3, $4, $5, $6) >= ts5
'
$

$ LANG=C date
Wed Jul  4 15:22:04 DFT 2007
$ log5.sh
$ log5.sh 30
gssjgu      pts/1       Jul  4 15:06    (1.1.1.11)  
$

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