Re: Escape Meta Chars in Character Classes

Just a guess, but it might be the - that has to be at the beginning or end
of the character class if it is not meant to be a range.

Kim

On Wed, 16 Dec 2015 16:52 Andreas Säger <[email protected]> wrote:

> Simplified and well working example:
>
> CREATE MEMORY TABLE T ("PAIRS" CHAR(3));
> INSERT INTO T VALUES('1,2');
> INSERT INTO T VALUES('1\2');
> INSERT INTO T VALUES('1+2');
> INSERT INTO T VALUES('1/2');
> INSERT INTO T VALUES('1.2');
> INSERT INTO T VALUES('1:2');
> INSERT INTO T VALUES('1;2');
> INSERT INTO T VALUES('1-2');
> INSERT INTO T VALUES('1&2');
>
>
> SELECT REGEXP_SUBSTRING("PAIR",'\d[-+/&.:;]\d') FROM "T";
>
> The regexp matches all records except the first and the second because
> comma and backslash are not in the character class. It matches one
> digit, followed by any record within character class [-+/&.:;], followed
> by another digit. It works as expected without escaping special
> characters because character classes are lists of literal characters.
>
> But when you change the order of characters within the class, you get an
> error
>
> > java.util.regex.PatternSyntaxException: Illegal character range near
> index 10
>
> when the last element of the character class is a metacharacter
> according to
> > http://docs.oracle.com/javase/tutorial/essential/regex/literals.html
>
> > The metacharacters supported by this API are: <([{\^-=$!|]})?*+.>
>
> or when the last character is a slash. May be there are even more "bad"
> characters.
>
> The following variants do raise the PatternSyntaxException and none of
> the escape methods can fix it:
> -- + at the end of class:
> SELECT REGEXP_SUBSTRING("PAIR",'\d[-/&.:;+]\d') FROM "T";
>
> -- . at the end of class:
> SELECT REGEXP_SUBSTRING("PAIR",'\d[-/&:;+.]\d') FROM "T";
>
> -- / at the end of class which is not even a metacharacter:
> SELECT REGEXP_SUBSTRING("PAIR",'\d[-&:;+./]\d') FROM "T";
>
> In other words: Certain characters need to be escaped when they are the
> last element of a character class or you put a "good" character at the end.
> Same as above but with last char escaped by \
> -- \+ at the end of class:
> SELECT REGEXP_SUBSTRING("PAIR",'\d[-/&.:;\+]\d') FROM "T";
>
> -- \. at the end of class:
> SELECT REGEXP_SUBSTRING("PAIR",'\d[-/&:;+\.]\d') FROM "T";
>
> -- \/ at the end of class which is not even a metacharacter:
> SELECT REGEXP_SUBSTRING("PAIR",'\d[-&:;+.\/]\d') FROM "T";
>
> A backslash in a character class needs to be escaped by a leading
> backslash in any case like the leading \\ in the following:
> SELECT REGEXP_SUBSTRING("PAIR",'\d[\\-&:;+.\/]\d') FROM "T";
>
>
> In my previous posting I wrote ...
> > Same problem with an escaped slash \/ and with \Q/\E too ...
>
>
> ... which I can not reproduce anymore. Both escaping methods fix the
> problem of "bad" char at the end of character classes.
> After all, I think all this is somewhat "normal" but what is "normal" in
> regexp context?
>
>
>
>
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