sed

Find empty lines and don't print them. In effect filtering out empty lines

sed -n '/^$/!p' file.txt

You can use this to filter out different matching lines as well.

sed -ni '/Path:\s*$/!p' file.txt

Match text and backreference

You can match some text with a regex. Put it in parentheses () called grouping. This way you put the matched text in a variable \1

sed -rie 's/(hoi).*/\1 blaat/' test1

Remove out commented lines and empty lines. Match all environment variables names defined in .env and replace the rest of the line with this find

egrep -v '^#|^$' ~/repos/docker-project/.env |sed -E 's/(.*)=.*$/\1/'

search line in file and replace based on match

sed -e  '/CN[-]*EXT/s/^/#/' -i gconv-modules

search line based on regex and delete that line

sed -i '/Amsterdam/d'

search line and delete if word Amsterdam is not found.

sed -i 'g!/Amsterdam/d'