* [9fans] regexp to match paragraphs in troff documents
@ 2007-06-07 14:28 Matthias Teege
2007-06-07 14:50 ` rog
2007-06-07 17:46 ` Russ Cox
0 siblings, 2 replies; 3+ messages in thread
From: Matthias Teege @ 2007-06-07 14:28 UTC (permalink / raw)
To: 9fans
Moin,
I've tried to pipe paragraphs of a troff document to fmt but I
have problems with the correct regular expression. My first attempt
"/^\.[A-Z]++.*\n(^[^]*)*\n^\.[A-Z]++.*\n/" matches only any second
paragraph because the expression is overlapping. Does anyone have a nice
idea to match troff parapgraphs?
Many thanks
Matthias
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [9fans] regexp to match paragraphs in troff documents
2007-06-07 14:28 [9fans] regexp to match paragraphs in troff documents Matthias Teege
@ 2007-06-07 14:50 ` rog
2007-06-07 17:46 ` Russ Cox
1 sibling, 0 replies; 3+ messages in thread
From: rog @ 2007-06-07 14:50 UTC (permalink / raw)
To: 9fans
> I've tried to pipe paragraphs of a troff document to fmt but I
> have problems with the correct regular expression. My first attempt
> "/^\.[A-Z]++.*\n(^[^]*)*\n^\.[A-Z]++.*\n/" matches only any second
> paragraph because the expression is overlapping. Does anyone have a nice
> idea to match troff parapgraphs?
it's not easy (maybe not possible?) to do what you're doing unless you
can unambiguously find the start and end of paragraphs (e.g. between ^\.PP and ^$),
in which case you can use something like:
,x/^\.PP/.,/^$/|fmt
for other cases, i suppose it might be nice to have non-greedy matching,
in which case you could do something like:
,x/^\.[A-Z][A-Z].*\n(.*\n)*?\.[A-Z][A-Z]\n/
russ: how easy do you think it would be to put non-greedy matching into
the acme/sam regexp engine?
PS. ++ means exactly the same as +
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [9fans] regexp to match paragraphs in troff documents
2007-06-07 14:28 [9fans] regexp to match paragraphs in troff documents Matthias Teege
2007-06-07 14:50 ` rog
@ 2007-06-07 17:46 ` Russ Cox
1 sibling, 0 replies; 3+ messages in thread
From: Russ Cox @ 2007-06-07 17:46 UTC (permalink / raw)
To: 9fans
matthias:
> I've tried to pipe paragraphs of a troff document to fmt but I
> have problems with the correct regular expression. My first attempt
> "/^\.[A-Z]++.*\n(^[^]*)*\n^\.[A-Z]++.*\n/" matches only any second
> paragraph because the expression is overlapping. Does anyone have a nice
> idea to match troff parapgraphs?
It looks like you'd be happy with
,y/^\..*\n/ |fmt
or, avoiding fmt of zero-length ranges (just a little faster)
,y/(^\..*\n)+/ |fmt
rog:
> for other cases, i suppose it might be nice to have non-greedy matching,
> in which case you could do something like:
> ,x/^\.[A-Z][A-Z].*\n(.*\n)*?\.[A-Z][A-Z]\n/
> russ: how easy do you think it would be to put non-greedy matching into
> the acme/sam regexp engine?
it's trivial but it doesn't make sense.
in plan 9 regular expressions (as in awk), the semantics
are that the leftmost longest overall match is chosen,
even if that means not repeating a * as much as possible.
for example, consider /a*(ab)?/ against "aab".
perl will match "aa" because the a* greedily grabs "aa"
leaving (ab)? no choice but to match the empty string.
plan 9 will match "aab" because that is a longer match:
the a* selflessly matches less so that the overall
expression can match more.
since plan 9 doesn't have the greedy-like-perl * operator,
it doesn't make sense to think about adding a
non-greedy-like-perl * operator.
the y iterator handles about 90% of the reasons people use
non-greedy operators, so i'm happy to leave things as is.
russ
^ permalink raw reply [flat|nested] 3+ messages in thread
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2007-06-07 14:28 [9fans] regexp to match paragraphs in troff documents Matthias Teege
2007-06-07 14:50 ` rog
2007-06-07 17:46 ` Russ Cox
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