Re: A Lua 5.2 string pattern issue
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- Subject: Re: A Lua 5.2 string pattern issue
- From: Roberto Ierusalimschy <roberto@...>
- Date: 2010年2月23日 15:02:04 -0300
> I've come across a new error when doing some compatibility tests with
> Lua 5.2 (work2, naturally!)
>
> -- escape.lua
> -- escape all magic characters except ,ドル which has special meaning
> -- Also, un-escape any characters after ,ドル so $( passes through as is.
> function escape (spec)
> return spec:gsub('[%-%.%+%[%]%(%)%^%%%?%*]','%%%1'):gsub('%$%%(%S)','%$%1')
> end
> print(escape '$({def} $')
>
> $ lua escape.lua
> $({def} $ 1
> $ lua52 escape.lua
> lua52: escape.lua:2: invalid use of '%' in replacement string
>
> Clearly something has changed; am I doing anything odd?
In the replacement string, '%' can only be followed by '%' or a digit:
* http://www.lua.org/manual/5.1/manual.html#pdf-string.gsub
If repl is a string, then its value is used for replacement. The
character % works as an escape character: any sequence in repl of the
form %n, with n between 1 and 9, stands for the value of the n-th
captured substring (see below). The sequence %0 stands for the whole
match. The sequence %% stands for a single %.
Your replacement string has a '%$', which has an undefined behavior. Lua
5.1 was more lenient about it.
-- Roberto