On Fri, Oct 30, 2015 at 10:01 PM, John Cowan <co...@mercury.ccil.org> wrote:
> Peter Bex scripsit: > > > Note the nonl, which the manual states is equivalent to ".", but of > > course nonl means "no newline". > > Dot in regular expressions has *always* meant "match any character but a > newline". It doesn't come up that much in Unix commands, which typically > process their input line by line anyway. But if you look at the Posix > definition or the Perl one, you see that dot is indeed equivalent to > "nonl". > Indeed, "nonl" exists in order to have an SRE equivalent for dot. > > > Maybe Alex can give us some info about why this is the case? I think > this > > may have something to do with the multi-line / single-line distinction > > (which, to be honest, I never really understood). > > Multi-line and single-line mean totally different things: you can use one > of them or both or neither. Multi-line mode means that ^ and $ will match > the beginning and end of a line as well as the beginning and the end of > the string. In non-multi-line mode, they match only the beginning and > the end of the string. Single-line mode means that dot matches newline; > non-single-line mode means that it does not. > Yes, exactly. The terminology "single-line" (/s) and "multi-line" (/m) come from Perl though, and I think are confusing. But these flags exist only for PCRE compatibility, so I don't think it's worth changing them. With SREs there is no confusion: you always say explicitly `any' or `nonl', `bol/eol' or `bos/eos'. Note this is the same in Ruby regexen (which also allows a /m flag). -- Alex
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