Shell Programming and Scripting

Hi,

I have a text file with sample records as

Code:

CASE ID: 20170218881083  
Original presentment record for ARN  [24013935350549886999873] not found
for Re-presentment

I want to extract the 23 digit number from this file. I thought of using grep but initially couldn't extract the required number. However, after googling, I found out the usage of

Code:

 -P, --perl-regexp: Interpret PATTERN as a Perl regular expression.

and

Code:

-o, --only-matching: Show only the part of a matching line that matches PATTERN.

I did manage to extract the 23 digit number from the sample text above using grep -Po as suggested in a forum, but am confused as to what the usage is for. Can someone please explain it and suggest any other commands which do the same work.

Code:

$ echo 'Original 123 presentment record for ARN  [24013935350549886999873] not found'|grep  -Po "\d{23}"

Code:

$ uname -a
Linux 2.6.18-417.el5 #1 SMP Sat Nov 19 14:54:59 EST 2016 x86_64 x86_64 x86_64 GNU/Linux