如何使用grep / sed提取子字符串和数字

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  
ipc 222  
stalls n shdmem 112

So say I only want to extract the data for miss rate which is 0.21 . How do I do it with grep or sed? Plus, I need more than one number, not only the one after miss rate . That is, I may want to get both 0.21 and 112 . A sample output might look like this:

0.21 222 112

Cause I need the data for later plot.

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

Answer 2

The grep -and- cut solution would look like:

to get the 3rd field for every successful grep use:

grep "^miss rate " yourfile | cut -d ' ' -f 3

or to get the 3rd field and the rest use:

grep "^miss rate " yourfile | cut -d ' ' -f 3-

Or if you use bash and "miss rate" only occurs once in your file you can also just do:

a=( $(grep -m 1 "miss rate" yourfile) )
echo ${a[2]}

where ${a[2]} is your result.

If "miss rate" occurs more then once you can loop over the grep output reading only what you need. (in bash)

Answer 3

Use awk instead:

awk '/^miss rate/ { print $3 }' yourfile

To do it with just grep, you need non-standard extensions like here with GNU grep using PCRE (-P) with positive lookbehind (?<=..) and match only (-o):

grep -Po '(?<=miss rate ).*' yourfile

Answer 4

If you really want to use only grep for this, then you can try:

grep "miss rate" file | grep -oe '\([0-9.]*\)'

It will first find the line that matches, and then only output the digits.

Sed might be a bit more readable, though:

sed -n 's#miss rate ##p' file

Answer 5

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

Answer 6

I believe

sed 's|[^0-9]*\\([0-9\\.]*\\)|\\1 |g' fiilename

will do the trick. However every entry will be on it's own line if that is ok. I am sure there is a way for sed to produce a comma or space delimited list but I am not a super master of all things sed.