UNIX for Dummies Questions & Answers

What is the significance of special characters used in grep command.
Like \ [ ] + ?

What is the meaning of the below command:

Code:

grep -o "0078\([0-9]\)\+" $i | sort | uniq

Can i replace + with ?

Thanks,
tinku

\( \) is used to remember the pattern so that you can recall it later
"+" means one or more matched pattern
"?" means one or zero matched pattern
So you probably can't replace + with ?

Take a look at this : Regular Expressions

Thanks thanhdat.

Just want to know whether my understandin of the below expression is correct.

grep -o "0034\([0-9]\)\+" => This will fetch all numbers starting with 0034
grep -o "0034[0-9]\+" => This will fetch anything that follows 0034. Say for example: 003483744 0034abcd
But the first one picks only 0034, followed by numbers. Am I Right?

Thanks,
Nanda

Did you test on your system, what did those commands return ?
In my test (with debian 5) it should be :

Code:

$cat test
1234
12qbc
1222 345345
12ABC!!

$egrep -o "12[0-9]+" test
1234
1222

And this command should be translated to : find all numbers starting with 12