Problems with '+' in grep

jlinkels · 12-03-2007, 03:03 AM

I am trying to valdiate an e-mail address. There are zillions of examples out on the internet, but whatever I use, my valid e-mail address is never validated.

It appears to boil down at the '+' character. For example when I try to match zero or more alpha characters I get a match:

Code:

jlinkels@jlinkels_lt:/var/www$ echo jlin@ab.an | grep '^[:alpha:]*'
jlin@ab.an

However, when I try to match ONE or more alpha's, I get a mismatch:

Code:

jlinkels@jlinkels_lt:/var/www$ echo jlin@ab.an | grep '^[:alpha:]+'

I don't get that, what I am asking is "match one or more alpha characters at the beginning of the string". Or am I?

I am using GNU grep 2.5.1

Obviously the real matching regexp is much more complicated, but since I even don't understand this simple example, it is unthinkable that I could use those.

jlinkels

bigearsbilly · 12-03-2007, 03:29 AM

use egrep

strangely grep -e doesn't work, which I always assumed was a synonym for egrep

colucix · 12-03-2007, 03:32 AM

I am not an expert about regular expressions, but from the grep man page

Quote:

In basic regular expressions the metacharacters ?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions \?, \+, \{, \|, \(, and \).

also I'd use the boundary tag \b which matches the empty string at the edges of a word, as in

Code:

$ echo jlin@ab.an | grep '\b[:alpha:]\+'
jlin@ab.an

I hope this will help a little, waiting for a real regexp guru...

bigearsbilly · 12-03-2007, 03:43 AM

egrep works !!!

ghostdog74 · 12-03-2007, 03:50 AM

Code:

# echo jlin@ab.an | grep -E "^[[:alpha:]]+"
jlin@ab.an

colucix · 12-03-2007, 03:55 AM

bigearsbilly, sorry but I didn't see your post before posting mine (just for a bunch of minutes), anyway I tried the expression from the OP with egrep and it doesn't work on my system:

Code:

$ echo jlin@ab.an | egrep '^[:alpha:]+'
$ <no-output>

bigearsbilly · 12-03-2007, 03:59 AM

what system?

colucix · 12-03-2007, 04:10 AM

Fedora Core 5, 2.6.20-1.2316.fc5, grep 2.5.1. Instead the one suggested by ghostdog74 works. But - I repeat - I am not a regexp guru, so I leave the correct explanation to you.

ghostdog74 · 12-03-2007, 04:11 AM

Quote:

Originally Posted by colucix

bigearsbilly, sorry but I didn't see your post before posting mine (just for a bunch of minutes), anyway I tried the expression from the OP with egrep and it doesn't work on my system:

Code:

$ echo jlin@ab.an | egrep '^[:alpha:]+'
$ <no-output>

Code:

# echo jlin@ab.an | egrep '^[[:alpha:]]+'
jlin@ab.an

bigearsbilly · 12-03-2007, 04:12 AM

are you sure, it works on my solaris and cygwin

bigearsbilly · 12-03-2007, 04:31 AM

ooops!

Code:

grep '^[[:alpha:]]+'

that's better

jlinkels · 12-03-2007, 03:50 PM

Hmmm weird. egrep works as expected,
grep doesn't,
grep -e doesn't
but grep -E does.

I think I only tried grep -e (I read the man page).

Is this a bug in grep?

I should be able to proceed from here. Thanks all.

jlinkels

ntubski · 12-03-2007, 05:20 PM

Quote:

Originally Posted by jlinkels

...
(I read the man page).
...

Are you sure you read the right page??

Quote:

Originally Posted by man grep

egrep is the same as grep -E.
...
-E, --extended-regexp
Interpret PATTERN as an extended regular expression (ERE, see
below). (-E is specified by POSIX.)
...
-e PATTERN, --regexp=PATTERN
Use PATTERN as the pattern. This is useful to protect patterns
beginning with hyphen-minus (-). (-e is specified by POSIX.)

chrism01 · 12-03-2007, 06:23 PM

For anyone attempting to validate an email address, I recommend reading this article (and comments/links): http://haacked.com/archive/2007/08/2...s-until-i.aspx

jlinkels · 12-04-2007, 02:46 AM

ntubski: I said I read it, I did not say I understood it.

But now it is clear. Thanks to the feedback here.

chrism01: Thanks, I'll study that. I was intending to use someone's else regexp anyway instead of desiging my own.

jlinkels