In every line in your file have only two digits, (here 12 is two digits), you can use one more way as,

[0-9]{2}

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If the number of digits is not fixed, use, 

[0-9]+

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You can get to know from man pages. You can store the values using $1 variable.

In reply to Re: Regex to extract number from text file by irah
in thread Regex to extract number from text file by premal

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