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

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/'

With GNU sed:

sed 's/pattern//2g'

The 2 specifies that the second pattern and all the restg should remove. So this will keep the first one.

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//'

The generic solutions to remove from the nth (3 for example) position are:

sed -e ':begin;s/pattern//4;t begin'
sed -e 's/\(pattern\)/\1\n/;h;s/.*\n//3;s/pattern//g;H;g;s/\n.*\n//'

Related