Shell Programming and Scripting

#!/bin/ksh
prevline=""
while read line; do
  pval=${prevline##* }
  val=${line##* }
  if (( val*pval > 0 )); then
    avg=$(( (val+pval)/2 ))
    printf "%s %1.1f\n" "${prevline% *}" $avg
    line=""
  elif [[ $prevline != "" ]]; then
    echo $prevline
  fi
  prevline=$line
done < infile
if [[ $prevline != "" ]]; then
  echo $prevline
fi

awk '{ if ( pval*$NF > 0 )
       { avg=(pval+$NF)/2
         sub(/ [^ ]*$/,"",prev)
         printf("%s %1.1f\n", prev, avg)
         $0=""
       }
       else if (prev != "")
         { print prev }
       sub(/ *$/,"")
       pval=prev=$0;
       sub(/.* /,"",pval)
     }
     END { if ( prev != "" )
           print prev
     }' infile