If you’ve ever tried to parse the output of "uptime",you know it can be complicated. There’s a simpler solution:Use the raw numbers from /proc/uptime. Here’s a simple script that spits out the days and remaining time in digital clock format:
cat /proc/uptime | awk ‘{printf "%d%s%.2d%s%.2d%s%.2d%s",$1/86400 ,"days,",$1%86400/3600 ,":",$1%86400%3600/60 ,":",$1%86400%3600%60 ,"\n"}’
Note that the output can be changed to your needs. See the AWK Tutorial for more info on using modulus (%) in calculations,and string formatting (i.e.,%d and %s)