Shell Programming and Scripting

#!/bin/ksh
in_total=`cat in_file | awk -F: '{in_total += $1 * 86400 + $2 * 3600 + $3 * 60 + $4} END {printf "%d\n",in_total} '`
out_total=`cat out_file | awk -F: '{out_total += $1 * 86400 + $2 * 3600 + $3 * 60 + $4} END {printf "%d\n",out_total} '`
(( total = in_total - out_total ))
print "Total is " $total

awk -F: ' FILENAME == "in_file" {
in_total += $1 * 86400 + $2 * 3600 + $3 * 60 + $4
} 
FILENAME == "out_file" {
out_total += $1 * 86400 + $2 * 3600 + $3 * 60 + $4
}
END {printf "%d\n",in_total - out_total } ' in_file out_file