Re: Less greedy pattern match

On Wednesday 16 April 2008 05:23, Ed Morton wrote:

> There's no "less greedy" operator (to be honest, I'm not sure what that
> really means or why it'd be more useful than a different RE)

Well, perl REs have non-greedy match. It can be useful, for example, when
parsing html or xml. The classical example is something like this (please
note that I'm not a perl guru - alas -):

$ cat file.html
<tag><section><t1>foo</t1><t2>blah</t2><t1>bar
</t1></section>
<section><t1>baz
</t1><t2>blah</t2><t1>baz</t1></section></tag>

Suppose you want to remove only what's inside <t1> tags (tags included)
and
keep everything else, without apriori knowledge of how the lines are
formatted.

The simple perl one-liner:

$ perl -p0e 's%<t1>.+?</t1>%%gs' file.html
<tag><section><t2>blah</t2></section>
<section><t2>blah</t2></section></tag>

does what can't be done with sed. The "+?" is the non-greedy notation
for "one or more", just like "*?" is the non-greedy operator for "zero or
more", etc.

Note that I'm not saying that that cannot be done using other
methods...that
was just an example to demonstrate how non-greedy match can be useful.

-- 
All the commands are tested with bash and GNU tools, so they may use
nonstandard features. I try to mention when something is nonstandard (if
I'm aware of that), but I may miss something. Corrections are welcome.