Regex » History » Version 2
Yingdi Yu, 03/19/2014 11:19 AM
1 | 1 | Yingdi Yu | # NDN Regular Expression |
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2 | 2 | Yingdi Yu | |
3 | NDN regular expression matching is done at two levels: one at the name level and one at the name component level. |
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5 | We use `<` and `>` to enclose a name component matcher which specifies the pattern of a name component. |
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6 | The component pattern is expressed using the [Perl Regular Expression Syntax](http://www.boost.org/doc/libs/1_55_0/libs/regex/doc/html/boost_regex/syntax/perl_syntax.html). |
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7 | For example, `<ab*c>` can match the 1st, 3rd, and 4th components of `"/ac/dc/abc/abbc"`, but it cannot match the 2nd component. |
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8 | A special case is that `<>` is a wildcard matcher that can match **ANY** component. |
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10 | Note that a component match can match only one name component. |
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11 | In order to match a name, you need to specify the pattern of a name based on the name component matchers. |
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12 | For example, `<ndn><edu><ucla>` can match the name `"/ndn/edu/ucla"`. |
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13 | In order to describe a more complicated name pattern, we borrow some syntaxes from the standard regular expressions. |
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15 | ## NDN Regex Syntax |
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17 | ### Anchors |
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19 | A '^' character shall match the start of a name. |
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20 | For example, `^<ndn>` shall match any names starting with a component `"ndn"`, and it will exclude a name like `"/local/broadcast"`. |
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22 | A '$' character shall match the end of a name. |
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23 | For example, `^<ndn><edu>$` shall match only one name: `"/ndn/edu"`. |
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26 | A NDN regular expression is built on the component matcher extended from the standard regex by simply treating a component matcher as a single character in standard regex. |
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27 | For example, |
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28 | `^<ndn>` can match any names starting with a component `"ndn"`; |
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29 | `<test>$` can match any names ending with a component `"test"`; |
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30 | `^[^<ndn>]` can match any names that do not start with a component `"ndn"`; |
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31 | `^([^<DNS>])<DNS>(<>*)<NS>` can match a NDN DNS data name, and you can use back reference to extract the part enclosed by `(` and `)` |
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32 | (`"\1\2"` can extract `/ndn/edu/ucla/irl` from `/ndn/edu/ucla/DNS/irl/NS/123456`. |