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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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[ambrus]: As for TeX, I'm not trying to discourage anyone from writing carefully beautifully typeset documents, in maths or outside. But most people aren't willing to do that, and will spend only little time about the formatting,
[ambrus]: and try to leave everything else to automated systems without checking how what they write came out format-wise, and for those people, discounting the part about journals with a specific format above,
[ambrus]: just blindly recommending to use LaTeX is a bad idea now.

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