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Posted to commits@daffodil.apache.org by GitBox <gi...@apache.org> on 2021/01/27 14:57:57 UTC
[GitHub] [incubator-daffodil] mbeckerle commented on pull request #481: ADD test for "%%" to bypass existing test for "%NL"
mbeckerle commented on pull request #481:
URL: https://github.com/apache/incubator-daffodil/pull/481#issuecomment-768342231
Yeah, regex are really hard without myregextester, and the explain regex site tools.
Here's a regex that matches even number of % followed by single % followed by either NL or ES followed by ";"
That is, it matches an "unescaped NL" or "unescaped ES".
```
(?:%%)*(%(?:NL|ES)\;)
```
You can of course generalize the NL|ES to the set of DFDL entities you want it to exclude.
Here's a test string:
```
%NL;abcd%%ES;efgh%NLijkl%%%%%NL;mnop
```
And here's the matchAll output as described by myregextester.com
```
$matches Array:
(
[0] => Array
(
[0] => %NL;
[1] => %ES;
[2] => %%%%%NL;
)
[1] => Array
(
[0] => %NL;
[1] => %ES;
[2] => %NL;
)
)
```
And here's the explanation of this per
http://rick.measham.id.au/paste/explain.pl?regex=%28%3F%3A%25%25%29*%28%25%28%3F%3ANL%7CES%29%5C%3B%29
```
NODE EXPLANATION
--------------------------------------------------------------------------------
(?: group, but do not capture (0 or more times
(matching the most amount possible)):
--------------------------------------------------------------------------------
%% '%%'
--------------------------------------------------------------------------------
)* end of grouping
--------------------------------------------------------------------------------
( group and capture to \1:
--------------------------------------------------------------------------------
% '%'
--------------------------------------------------------------------------------
(?: group, but do not capture:
--------------------------------------------------------------------------------
NL 'NL'
--------------------------------------------------------------------------------
| OR
--------------------------------------------------------------------------------
ES 'ES'
--------------------------------------------------------------------------------
) end of grouping
--------------------------------------------------------------------------------
\; ';'
--------------------------------------------------------------------------------
) end of \1
```
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