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Re^3: regex: negative lookahead

by kennethk (Abbot)
on Dec 05, 2011 at 16:38 UTC ( #941894=note: print w/replies, xml ) Need Help??


in reply to Re^2: regex: negative lookahead
in thread regex: negative lookahead

The difference is a lookahead versus a lookbehind. If you ignore the lookahead/lookbehind because they are zero width (don't consume characters), you would expect /^($start(\w+(,\s)?)+)$/ to grab an entire string between start and finish. When you get to the part of the regular expression where you have your assertion, the cursor is here:
log4j.rootLogger=INFO, FILE, SYSLOG ^
If you look ahead of this position, there is nothing, which clearly passes the negative lookahead check. The offending string is behind your position, thus you need a negative lookbehind.

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[choroba]: (well, it comes from the 14th century, so labelling it as "modern" doesn't seem appropriate)
[Your Mother]: "They" is becoming accepted but it irritates me sometimes. I tend to just pick she or he randomly or try to use "one."
LanX thinks it is appropriate here :)
[Your Mother]: They would think so.
[jdporter]: ok, I need a recipe for piping lines "through" an external program which is itself a filter
[jdporter]: without using a tmp file
[1nickt]: tobyink perl -MTypes::Standard= is_Int -Mstrict -wE 'say 1 if is_Int 1.0'
[jdporter]: so that I can use the existing expand unix util. Otherwise, I'll probably use Text::Tabs.
[1nickt]: pryrt I guess I don;t really care if user 42 logs on as 42.0 ... more of an academic question at this point.
[LanX]: jdporter: open PIPE,'-|' ?

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