Simple regexp : \s or \S
moo...@yahoo.co.uk
I have a small regexp issue that I hope someone can clarify. I am
attempting to use a regular expression that identifies lines that
contain only comments.
e.g.
set a { # Comment Only (with some spaces)}
set b { Stuff # Comment at end of line}
If I use
% regexp {^\s*#} $a
1
% regexp {^\s*#} $b
0
The question is, why does the following not work
% regexp {\S*#} $b
1
man re_syntax implies that \S* should be equivilant to ^\s*.
Clarification greatly appreciated.
Steven
p.s. I assume that it would be easier using the string commands?
Jonathan Bromley
>man re_syntax implies that \S* should be equivilant to ^\s*.
I suspect you're getting confused between ^ used to negate
a character class, and ^ used to mean "start of string".
The RE [^abc] means "any character that's not in the set [abc]".
So [^\s] is indeed the same as \S - it means "any character
that's not whitespace". But ^\s means something quite different -
it matches a single whitespace character at the start of the string.
If your string begins with something other than whitespace, it
simply won't match.
>The question is, why does the following not work
>% regexp {\S*#} $b
The "negated" form you were looking for should probably be
regexp {^[^\S]*#}
but, since \S is itself a shorthand for [^\s], this is illegal;
in any case, it's kinda silly :-)
--
Jonathan Bromley, Consultant
DOULOS - Developing Design Know-how
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Doulos Ltd., 22 Market Place, Ringwood, BH24 1AW, UK
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moo...@yahoo.co.uk
wrote:
> On Tue, 26 Jun 2007 05:10:51 -0700, moo...@yahoo.co.uk wrote:
> >man re_syntax implies that \S* should be equivilant to ^\s*.
>
> I suspect you're getting confused between ^ used to negate
> a character class, and ^ used to mean "start of string".
>
> The RE [^abc] means "any character that's not in the set [abc]".
> So [^\s] is indeed the same as \S - it means "any character
> that's not whitespace". But ^\s means something quite different -
> it matches a single whitespace character at the start of the string.
> If your string begins with something other than whitespace, it
> simply won't match.
>
> >The question is, why does the following not work
> >% regexp {\S*#} $b
>
> The "negated" form you were looking for should probably be
>
> regexp {^[^\S]*#}
>
> but, since \S is itself a shorthand for [^\s], this is illegal;
> in any case, it's kinda silly :-)
> --
> Jonathan Bromley, Consultant
>
> DOULOS - Developing Design Know-how
> VHDL * Verilog * SystemC * e * Perl * Tcl/Tk * Project Services
>
> Doulos Ltd., 22 Market Place, Ringwood, BH24 1AW, UK
>
> The contents of this message may contain personal views which
> are not the views of Doulos Ltd., unless specifically stated.
Thanks Jonathan,
You are correct in that this was the source of my confusion. Having re-
read the man page, it starts to make sense
Steven