How to extract a value from a string using regex and a shell?

Question

I am in shell and I have this string: 12 BBQ ,45 rofl, 89 lol

Using the regexp: \\d+ (?=rofl), I want 45 as a result.

Answer 1

It seems that you are asking multiple things. To answer them:

• Yes, it is ok to extract data from a string using regular expressions, that's what they're there for
• You get errors, which one and what shell tool do you use?

• You can extract the numbers by catching them in capturing parentheses:

  .*(\d+) rofl.*
  

  and using $1 to get the string out (.* is for "the rest before and after on the same line)

With sed as example, the idea becomes this to replace all strings in a file with only the matching number:

sed -e 's/.*(\d+) rofl.*/$1/g' inputFileName > outputFileName

or:

echo "12 BBQ ,45 rofl, 89 lol" | sed -e 's/.*(\d+) rofl.*/$1/g'