Re: Patterns that cope with beginnings and end of strings

[Paul K <paulclinger@...>]

> I must be missing something obvious.  Any pointers?
> > =("all all ball all"):gsub("%f[%S]all%f[%s%z]", "none")
> all none ball none      2

Something like this?

> ("all all ball all"):gsub("%f[%w]all%f[%W]", "none")
"none none ball none" 3

Paul.

On Thu, Aug 1, 2013 at 5:12 PM, Geoff Leyland <geoff_leyland@fastmail.fm> wrote:
> Hi,
>
> I think I must have missed something fundamental with patterns - I keep having trouble with beginnings and ends of strings.  Suppose I have the nonsense string "all all ball all" and I'd like to change all the "all"s (but not the ball) to "none".
>
> This requires detecting either a space or the start of a string before "all" or a space or the end of a string after "all".  I'd guess I'd like to write the patterns [ ^] and [ $], but they don't work.
>
> I can detect the end of a string or a space with "%f[%s%z]", but I can't work out how to detect the beginning of a string or a space.
>
> I must be missing something obvious.  Any pointers?
>
> Cheers,
> Geoff
>
>
> $ lua
> Lua 5.1.5  Copyright (C) 1994-2012 Lua.org, PUC-Rio
>> =("all all ball all"):gsub("all", "none")
> none none bnone none    4
>> =("all all ball all"):gsub("(%s)all(%s)", "%1none%2")
> all none ball all       1
>> =("all all ball all"):gsub("([ ^])all([ $])", "%1none%2")
> all none ball all       1
>> =("all all ball all"):gsub("%f[%S]all%f[%s]", "none")
> all none ball all       1
>> =("all all ball all"):gsub("%f[%S]all%f[%s%z]", "none")
> all none ball none      2
>> return ("all all ball all"):gsub("%f[%S]all%z", "none")
> all all ball all        0
>
>