POSIX Regex: Exclude a specified word in the list using Regex

Question

I have a below word list:

www.home.example.com
www.example.com
home.example.com
google.com
example.com
child.example.com
sameer.example.com
sameer.google.com

I need a regex which only matches child domains of example.com, meaning I need the below answer:

www.home.example.com
home.example.com
child.example.com
sameer.example.com

But without using egrep -v option.

I have tried egrep -i '(([(a-zA-Z0-9\-\.|^www)]*)\.example\.com)' but did not work. Any help will be highly appreciated.

@WiktorStribiżew, looks like this is working, make it as a answer, so that I can upvote your answer. — manjesh23, May 04 '17 at 07:27
@WiktorStribiżew, but is there a way I can skip using -v? Because not sure whether my device will support -v or not. Can I use something like `!` — manjesh23, May 04 '17 at 07:31
Then I need to know if this is the actual data. Are you really after excluding a `red` line? Or is it just a "placeholder" and the real data is more complex? — Wiktor Stribiżew, May 04 '17 at 07:32
Possible duplicate of [How do I find all files that do not begin with a given prefix in bash?](http://stackoverflow.com/questions/21368838/how-do-i-find-all-files-that-do-not-begin-with-a-given-prefix-in-bash) — ceving, May 04 '17 at 07:35
@ceving: Well, it is a bit different since the whole line needs to be "excluded", but OP is updating the question now, so it might turn out the solution will be even more "different". — Wiktor Stribiżew, May 04 '17 at 07:38
@ceving, now modified the question and this is no more a duplicate, — manjesh23, May 04 '17 at 07:38
Why is `sameer.google.com` expected to match? Isn't it a subdomain of `google.com`? Then, `sameer.example.com` should also be an expected match. — Wiktor Stribiżew, May 04 '17 at 07:40
@WiktorStribiżew, requesting you to delete your answer for now which has the keyword red, just to avoid down votes. — manjesh23, May 04 '17 at 07:49
You might use a PCRE regex with `-P` option as Roman suggests. There is a way to use it without PCRE option, I believe, but it will be rather messy then. — Wiktor Stribiżew, May 04 '17 at 07:52
My device uses POSIX, PCRE is not supported on my device and I am using a custom kernel. — manjesh23, May 04 '17 at 07:55
`grep -v` is specified by POSIX. Is there some actual reason to not use it (i.e. is there some actual system that doesn't have it)? Or is this more like a puzzle? — ilkkachu, May 04 '17 at 08:14
@manjesh23: You may l remove the question if *you* want to get rid of minus points. Your requirements are rather puzzling. — Wiktor Stribiżew, May 04 '17 at 08:18
I removed my answer. Perhaps, you can only remove a question if there is only one unupvoted answer. I do not know as I never asked a question on SO. — Wiktor Stribiżew, May 04 '17 at 09:45

RomanPerekhrest · Answer 1 · 2017-05-04T08:10:39.750

1

grep approach (with PCRE):

grep -Pi '(?<!www)\.example\.com' file

without PCRE:

cat file | grep -Ei '\.example\.com' | grep -Ev '^w{3}\.example\.com'

The output:

www.home.example.com
home.example.com
child.example.com
sameer.example.com

edited May 04 '17 at 08:10

answered May 04 '17 at 07:44

RomanPerekhrest

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My device uses POSIX, PCRE is not supported on my device and I am using a custom kernel. – manjesh23 May 04 '17 at 07:57
@WiktorStribiżew, to not use `-v` in this case is just a whim, I suppose – RomanPerekhrest May 04 '17 at 08:16

ilkkachu · Answer 2 · 2017-05-04T08:12:15.030

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I'm not sure what it is you want to exclude, since you say you want to match only those in a given domain. If the words are in a file on separate lines, shouldn't a match locked to the end-of-line do?

grep -e '\.example\.com$' domains

If you want to exclude something after that, then just use grep -v, it's part of POSIX anyway.

edited May 04 '17 at 08:12

answered May 04 '17 at 08:08

ilkkachu

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he wanted to exclude `www.example.com` – RomanPerekhrest May 04 '17 at 08:10
@RomanPerekhrest, yeah, the sample output was missing that. But the question didn't say what the rule is that excludes it. – ilkkachu May 04 '17 at 08:13

POSIX Regex: Exclude a specified word in the list using Regex

2 Answers2