# print first 30 lines
sed 1,30d log.log

# delete first 30 lines
sed -e 1,30d log.log

# delete 17th lines
sed -e 17d log.log

# delete last 20 lines
sed -e '10,$d' log.log


# delete last 20 lines and backup file that named 'log.log.bak'
sed -e '10,$d' -i '.bak' log.log


# replace StdOut
sed -e 's/__variable__/__replaced__/g' file.txt

# replace in file
sed -e's/__variable__/__replaced__/g' -i '' file.txt