Here's a one-liner: 
ps -p $pid -o etime --no-heading|perl -aF'[:-]' -nE'say+pop(@F)+60*pop
+(@F)+3600*pop(@F)+84600*pop@F'

[download]

In reply to Re: A regular expression that will work for (hh:)mm:ss [converting clock time to seconds] by JavaFan
in thread A regular expression that will work for (hh:)mm:ss [converting clock time to seconds] by aware74

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