Re: On zero-width negative lookahead assertions

The following works if you break it into two expressions, but I can't see why yours doesn't match.

  perl -ne '/^root:\s*/ and $_ !~ /admin\@somewhere\.here/ and print' 
+alias
[download]

Update: Moving it around also works:

  perl -ne '/^root:(?!\s*admin\@somewhere\.here)/ and print' alias
[download]

pbeckingham - typist, perishable vertebrate.

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Re^2: On zero-width negative lookahead assertions by bronto (Priest) on Sep 10, 2004 at 14:25 UTC
`perl -ne '/^root:\s/ and $_ !~ /admin\@somewhere\.here/ and print' alias`* That's ok, but I want to understand that blah-blah-look-ahead thing `perl -ne '/^root:(?!\sadmin\@somewhere\.here)/ and print' alias`* This works! But I can't understand why it doesn't work if you put the \s* outside the parens, nor I can understand why it stops working if I put the \s$ at the end of the regex `:-(` Thanks a lot Ciao! `--bronto` In theory, there is no difference between theory and practice. In practice, there is.*	[reply] [d/l] [select]
Re^3: On zero-width negative lookahead assertions by Crian (Curate) on Sep 10, 2004 at 14:51 UTC
> But I can't understand why it doesn't work if you put the \s* outside the parens, nor I can understand why it stops working if I put the \s$ at the end of the regex :-( That is because if you have the string `root: admin@somewhere.here 11111233333333333333333333` [download] and the RE `/^root:\s(?!\s*admin\@somewhere\.here)/ ABBBBBCCC` [download] then the part A in the RE matches the beginning of the string, part BBBBB matches 11111 ("root:") and CCC matches an empty string (not a space, a string with zero chars in it). After this empty string follows a space, and the space is not the beginning of "admin@somewhere.here", because it is the beginning of " admin@somewhere.here". I hope things are getting clearer for you :-)	[reply] [d/l] [select]


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