sed: delete all occurrences of a string except the first one

Question

I have a logfile with timestamps in it. Occasionally there are multiple timestamps in one line. Now I would like to remove all of the timestamps from a line but keep the first one.

I can do s/pattern//2 but that only removes the second occurrence and sed doesn't allow something like s/pattern//2-.

Any suggestions?

Answer 1

This should work (replace _ by something else should it clash with your logs):

sed -e 's/pattern/_&/1' -e 's/\([^_]\)pattern//g' -e 's/_\(pattern\)/\1/'

Answer 2

sed -e ':begin;s/pattern//2;t begin'

or without the sed goto:

sed -e 's/\(pattern\)/\1\n/;h;s/.*\n//;s/pattern//g;H;g;s/\n.*\n//'