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

Using the special look around regex trick \K with pcre engine with grep :

grep -oP 'miss rate \K.*' file.txt

or with perl :

perl -lne 'print $& if /miss rate \K.*/' file.txt