Re: Regex: behaviour of ? after () atom

[Rich Felker <dalias@libc.org>]

On Fri, Sep 07, 2018 at 03:38:05PM +0200, Steffen Nurpmeso wrote:
> Hello.
> 
> In perl this is
> 
>   $x="print 1 2";
>   if($x =~ /^(:[[:space:]]+)?([^[:space:]]+)(.*)$/){ 
>     print "<$0> -> <$1> <$2> <$3>\n"
>   }
> 
> and the result is
> 
>   </tmp/t.pl> -> <> <print> < 1 2>
> 
> Now the same on AlpineLinux edge and musl-1.1.19-r10 with the MUA
> i maintain, which uses the normal regex stuff and calls it via
> 
>   echo eins=$3
>          vput vexpr i regex "${3}" \
>             '^(:[[:space:]]+)?([^[:space:]]+)(.*)$'  \
>             '<\$0> -> <\$1> <\$2> <\$3>'
>   echo i=$i
> 
> which in C code does 
> 
>       if((reflrv = regcomp(&re, argv[2], reflrv))){
>           ...
>          goto jestr;
>       }
>   fprintf(stderr, "GOING for <%s> -> <%s> %u\n",
>   argv[1],argv[2],n_NELEM(rema));
>       reflrv = regexec(&re, argv[1], n_NELEM(rema), rema, 0);
> 
> and overall prints
> 
>   eins=print 1 2
>   GOING for <print 1 2> -> <^(:[[:space:]]+)?([^[:space:]]+)(.*)$> 17
>   i=<print 1 2> -> <> <> <>
> 
> It works correctly if i remove the ()? atom, so i thought i should
> report that.

What is the value of the flags argument you passed to regcomp?

Rich