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Re^4: Quick Regex Question

by AnomalousMonk (Canon)
on Oct 09, 2012 at 12:36 UTC ( #998001=note: print w/replies, xml ) Need Help??


in reply to Re^3: Quick Regex Question
in thread Quick Regex Question

... using a zero-width negative look-ahead assertion; or ... using a z +ero-width positive look-ahead assertion together with \D ...

Note that  (?!\d) and  (?=\D) are not complementaryequivalent. The  (?!\d) assertion is satisfied by having any non-digit follow it or by nothing, i.e., by the end of the string, nothing being not-a-digit. The  (?=\D) assertion must be followed by a non-digit character. And similarly with the  (?<!\d) and  (?<=\D) look-behinds.

>perl -wMstrict -le "my $s = 'xyzINC1234567'; ;; print 'negative assertion true' if $s =~ /INC\d{7}(?!\d)/; print 'positive assertion true' if $s =~ /INC\d{7}(?=\D)/; " negative assertion true

In this behavior,  (?!\d) and, in general,  (?!character-or-character-class) and its negative look-behind cousin are similar to (but not exactly the same as) the  \b assertion, which may be true at the beginning or end of a string.

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[tye]: probably something in the init subsystem that does the mounting that you could disable and reboot.
davido needs to close laptop to board flight home from yapc.
[davido]: I'll look into it in a few hours probably.
[davido]: when i do get to that point I think I'll do it in a vm snapshot just in case. :)
[oiskuu]: tye, you were right: loginuid/sessionid are part of task struct if compiled with AUDITSYSCALL. I have some doubts if you should actually depend on that feature.
[Corion]: oiskuu: Depends on what you want to do with that information
[tye]: I'm not depending on that feature. But I could in this environment. I'm using getlogin(). shrug
[Corion]: For benign logging (which user started this DB instance), it's OK
[tye]: We use auditd for security monitoring. So we can rely on auditing being enabled. I'm not sure who would want to not be able to audit. Maybe some VM inside another system with audit?
[SuicideJunkie]: spies would want a system to not be able to audit.

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