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

Code:

echo 'Original presentment record for ARN  [24013935350549886999873] not found' | awk -F'[][]' '/^Original presentment/ {print $(NF-1)}'

Hi that command will extract all 23 digit numbers from the text. The -o option is a GNU and BSD grep extension.

You do not need the perl extension.

Code:

grep  -Eo "[0-9]{23}" file

should work as well

The problem with this command is that it will also return part of numbers that are larger than 23 digits if present..

So it should be:

Code:

grep  -Eo '\<[0-9]{23}\>' file

An equivalent awk command would be:

Code:

awk '$1~/^[0-9]{23}$/{print $1}' RS=\[ FS=\] file

---
( grep -Eo '\<\d{23}\>' file will also work with BSD grep )

Sed alternative

Code:

sed -n 's/.*\[\([0-9]\{23\}\)\].*/\1/p' filename

@vgersh. awk -F ' ' is for defining delimiters as far as I know, what does your command mean

Code:

awk -F'[][]'

. The next part is the start of the string I got that and I think $NF would be number of fields, but why are you subtracting 1 from it and then printing that out.

@Scrutinizer: true my command did print out numbers more than 23 in length.

Code:

grep  -Eo '\<[0-9]{23}\>' file

the above command should work perfect as square brackets wont be in delimiters always so the awk command wont work in all occasions.

I am kinda confused as to why we are using single quotes in a grep expression. Cos I was reading the other day that single quotes remove any meaning from the special characters. Shouldn't we use double quotes?

Also the fact the you have used <,>. Are they working as a block to extract only 23 digits numbers/characters?

---------- Post updated at 04:33 PM ---------- Previous update was at 04:25 PM ----------

@andy391791

I tweaked your command a bit cos the square brackets may or may not be present in future texts for finding the 23 digit number. The tweak seems to be working fine

Code:

$ echo 'Original presentment record for ARN  24013935350549886999873 not found'|sed -n 's/.*\([0-9]\{23\}\).*/\1/p'
24013935350549886999873
[dsiddiqui@lxserv01 scripts]$ echo 'Original presentment record for ARN  [24013935350549886999873] not found'|sed -n 's/.*\([0-9]\{23\}\).*/\1/p'
24013935350549886999873

but when I increase the length of the 23 digit number and run the command, it just extracts 23 numbered digits from the complete numeric strings and pastes it, which is not the case that I want. I just want to print 23 digits only if present

-F defines field delimiters. In this particular case the field delimiters are [] as the 23-digit long string is surrounded by [].
We subtract 1 from $NF because the LAST field is following the ]. The field next to last is your 23-digit long string.

Hi dsid

The single quotes are better at protecting the regular expression from the shell, than double quotes, so that is why I prefer to use them. When you read that they remove any meaning from the special characters, they meant shell special characters, not regex special characters ...

\< and \> are word boundary operators and match the empty string at the beginning/end of a word respectively..

So if the 23 digits are enclosed by anything other than word characters ( [0-9A-Za-z_], or more precisely: [[:alnum:]_] , including the start or end of a line) then it will match the 23 digits.