How to get the line count of a large file, at least 5G

Question

How to get the line count of a large file, at least 5G. the fastest approach using shell.

Answer 1

Step 1: head -n filename > newfile // get the first n lines into newfile，e.g. n =5

Step 2: Get the huge file size, A

Step 3: Get the newfile size,B

Step 4: (A/B)*n is approximately equal to the exact line count.

Set n to be different values,done a few times more, then get the average.