awk

Commands

# sum third column and print
awk '{sum += $3} END{print sum;}'

# print 5 column if 4 column is equal to 0
awk '$4 == 0 {print $5}'

# Show first 5 rows and all rows with regex match
watch -d -n 10 "nats stream list | awk 'NR<=5 {print; next} /netwo/'"

# Sum sizes
awk '/kb|KB/ {sum += $1 / 1024} /mb|MB/ {sum += $1} /gb|GB/ {sum += $1 * 1024} END {printf "Sum, MB: %.2f MB\nSum, GB: %.2f GB\n", sum, sum / 1024}'