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My problem is about a regex. Thanks to regexr, I managed to write up an expression that matches the interface name route linux command gave me.

But I can't catch it with:

route | grep -Eo "(?:((\w|\.|\*)+\s+)){7}([^ .]+[0-9]+)$"

Why is that?

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  • The immediate issue I see is you are using regexr with the regex wrapped in /(?:((\w|\.|\*)+\s+)){7}([^ .]+[0-9]+)$/igm. And when you are using grep it is just (?:((\w|\.|\*)+\s+)){7}([^ .]+[0-9]+)$. Since you desire a multiline grep that just doesn’t exist; grep is strictly one line at a time. – Giacomo1968 Nov 3 '14 at 4:24
  • There are a bunch of different regex dialects. grep -E and JavaScript (regexr's dialect, from a quick look) don't use the exact same one, so you can only use the regexr output as a starting point. – jjlin Nov 3 '14 at 6:51
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Different programs (and different versions of said program) might use different regex implementations. Try reducing or breaking down your regex part by part to know which feature is supported/is not supported.

For example, I need to remove the non-capturing group specifier ?: from your example so that my GNU grep can run as expected in Solaris 11.

Or you can try to replace -E with -P to use Perl regex engine which, in my case, make my GNU grep able to run your regex without further modifications.

route | grep -Po "(?:((\w|\.|\*)+\s+)){7}([^ .]+[0-9]+)$"

Note: GNU grep in Solaris 11 is located in /usr/gnu/bin/grep

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