how to extract substring and numbers only using grep/sed

Question

I have a text file containing both text and numbers, I want to use grep to extract only the numbers I need for example, given a file as follow:

miss rate 0.21          


        

Answer 1

You can use:

grep -P "miss rate \d+(\.\d+)?" file.txt

or:

grep -E "miss rate [0-9]+(\.[0-9]+)?"

Both of those commands will print out miss rate 0.21. If you want to extract the number only, why not use Perl, Sed or Awk?

If you really want to avoid those, maybe this will work?

grep -E "miss rate [0-9]+(\.[0-9]+)?" g | xargs basename | tail -n 1