Uptime

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# 11.8. Uptime

As with load, the data available through uptime is very difficult to parse. Again, if you have the `/proc/` filesystem, take advantage of it. I wrote the following code to output just the time the system has been up:

    #!/bin/bash
    #
    #   upt - show just the system uptime, days, hours, and minutes

    let upSeconds="$(cat /proc/uptime) && echo ${temp%%.*})"
    let secs=$((${upSeconds}%60))
    let mins=$((${upSeconds}/60%60))
    let hours=$((${upSeconds}/3600%24))
    let days=$((${upSeconds}/86400))
    if [ "${days}" -ne "0" ]
    then
       echo -n "${days}d"
    fi
    echo -n "${hours}h${mins}m"

Output looks like "1h31m" if the system has been up less than a day, or "14d17h3m" if it has been up more than a day. You can massage the output to look the way you want it to. This evolved after an e-mail discussion with David Osolkowski, who gave me some ideas.

Before I wrote that script, I had a couple emails with David O, who said "me and a couple guys got on irc and started hacking with sed and got this: uptime | sed -e 's/.* \(.* days,\)\? \(.*:..,\) .*/\1 \2/' -e's/,//g' -e 's/ days/d/' -e 's/ up //'. It's ugly, and doesn't use regex nearly as well as it should, but it works. It's pretty slow on a P75, though, so I removed it." Considering how much uptime output varies depending on how long a system has been up, I was impressed they managed as well as they did. You can use this on systems without `/proc/` filesystem, but as he says, it may be slow.

Relative speed: the "upt" script takes about 0.68 seconds on an unloaded 486SX25 (half that as a function). Contrary to David's guess, his use of sed to parse the output of "uptime" takes only 0.22 seconds.

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