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  • Romeo Bravo thinks this is interesting:

Excludes a and b.

From

Cover of Troubleshooting OpenVPN

Note

ha@ha ~ $ cat test
a
b
aa
bb
ab
ba
i
ii
abacab
backdoor
cab
test

%TRab(aba)+.,?=

A
B

ha@ha ~ $
ha@ha ~ $ grep [^ab] test
i
ii
abacab
backdoor
cab
test

%TRab(aba)+.,?=

A
B
ha@ha ~ $