Re: Seeker of Regex Wisdom (strings which don't form specific patterns)

Do you want to match lines with IP addresses that start with a comment?

grep '^#.*(?:[0-9]{1,3}\.){3}[0-9]{1,3}'

If you want you can 'trap' the IP address and just print that as well. Or did I miss the question?

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Re^2: Seeker of Regex Wisdom (strings which don't form specific patterns) by ilcylic (Scribe) on Aug 13, 2015 at 15:43 UTC
No, although I can see why my examples would lead one to think that. Doh. :( My question is really more about testing for the effects of awk. Since awk by default splits lines on whitespace, if I were to cat a file that contained a line that looked like `MY_IP = 123.134.234.90`, and then do `\|awk '{print $1;}'`, I'd only get the "MY_IP" part. So, in order to see what I would be losing by doing that, I decided to try and write a regex that would show me lines that contained an IP address, but only after the first whitespace on the line, which itself needed to follow some non-whitespace stuff, that did not itself contain an IP address. This turns out to be difficult to do by hand, but easy if you use regex modules, as shown below by AnomalousMonk :D	[reply] [d/l] [select]

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Re^2: Seeker of Regex Wisdom (strings which don't form specific patterns)
by ilcylic (Scribe) on Aug 13, 2015 at 15:43 UTC

No, although I can see why my examples would lead one to think that. Doh. :(

My question is really more about testing for the effects of awk. Since awk by default splits lines on whitespace, if I were to cat a file that contained a line that looked like MY_IP = 123.134.234.90, and then do |awk '{print $1;}', I'd only get the "MY_IP" part.

So, in order to see what I would be losing by doing that, I decided to try and write a regex that would show me lines that contained an IP address, but only after the first whitespace on the line, which itself needed to follow some non-whitespace stuff, that did not itself contain an IP address.

This turns out to be difficult to do by hand, but easy if you use regex modules, as shown below by AnomalousMonk :D

[reply]
[d/l]
[select]