[SOLVED] grep -w does not find the statement I am searching for

Jason_25 · 09-06-2022, 07:26 PM

This does not work as expected. Nothing is returned with -w. If I remove the -w then stuff with port :22 will be found. But the problem is stuff can also be on port :2212345 and that will be caught. How do I filter just :22 ?

Code:

NOOK_CHECK_3=$(echo $NOOK | grep -w ":22 " | wc -l)

astrogeek · 09-06-2022, 08:07 PM

Try this as your grep expression:

Code:

grep ":22\b"

That looks for ":22" followed by a word boundary, either a non-word character or end of line.

grail · 09-06-2022, 09:51 PM

As usual, if you show an example of the input and the desired output, it is always easier to assist.

My first thought would be that there is no boundary between the colon and the ip address

boughtonp · 09-07-2022, 08:04 AM

As per the Grep documentation:

Quote:

Originally Posted by https://www.gnu.org/software/grep/manual/html_node/Matching-Control.html#index-_002dw

-w
--word-regexp

Select only those lines containing matches that form whole words. The test is that the matching substring must either be at the beginning of the line, or preceded by a non-word constituent character. Similarly, it must be either at the end of the line or followed by a non-word constituent character. Word constituent characters are letters, digits, and the underscore. This option has no effect if -x is also specified.

Using -w means the space at the end of the pattern is likely redundant, but also that a port number is not going to work if there is a word character before the colon - as would be the case if the port is preceded by a valid hostname.

Removing the -w option and replacing the space with a \b will prevent longer ports matching and may be sufficient, but - depending on the specific input - might involve false positives (and thus have an incorrect check value and a bug in the script).

There's also several ways the check can probably be simplified/optimized, but not much point going there without example input and details of the context.

Jason_25 · 09-07-2022, 12:25 PM

Well it works now. I did try reading that manual page but my attention started fading after the word "Regex". I pretty much shutdown after that. I'm still not sure what you would use -w for other than if you wanted to spend all day cooped up in your office.

Anyway using \b works fine. I did try using it before because it is one of the most prominent solutions you find after searching. But bugs in my script were leading me to believe it was not working. $NOOK was getting cleared out before it was supposed to in short.

I don't know how it all works really. It is like magic that it can find :80 and :80. but not :8012345 which as we all know there are only like 65000 some ports available anyway. I mean someone obviously programmed it that way but it was well done.

MadeInGermany · 09-10-2022, 01:49 PM

The

Code:

grep ":22 "

is most precise, having real delimiting characters.

The

Code:

grep -w "22"

is a quick and dirty (and less precise) alternative.
It is identical with

Code:

grep "\b22\b"