Thanks Bob, Andrea and Members !
For those who did not follow my previous post, what I want is to have an
expression that matches something but not an empty string.
> From: "Bob Showalter"
> Hmm, why do you want to use a regex?
(1) Of course, I could use if ($key==$cid) {};
However, I just wanted to understand more about regular expressions, and the
reason why $key (having a value of 1234) matches an empty string. Andrea
have given me an explanation on why $key (having a value of 1234) matches an
empty string but I still need some clarification, Members please see further
down.
> Anyway, you need:
> $key =~ /^$cid$/
> But you need to be careful about what characters $cid
> might contain, so you're better to say:
> $key =~ /^\Q$cid\E$/;
> which is equivalent to the much more straightforward:
> $key eq $cid;
(2) Precisely, this is what I want ! A much more straightforward
expression equivalent to $key eq $cid;
[I copy & paste here]
> From Andrea Holstein <[EMAIL PROTECTED]>
> $cid is an empty string.
> So in reality there's written $key =~/\b\b/.
(3) I understand so far.
> \b stands for a word boundary and has a length of 0.
(4) Is this boundary \b equivalent to an empty string? What is the meaning
of 0 length? Is 0 lenght = empty string?
> In $key there are two word boundary,
> before the 1 and after the 4.
(5) Therefore are you saying that $key is equivalent to \b1234\b and when
match with an empty string, obviously they matched. Have I read you
correctly?
Hmmmm ! very interesting.
(6) So what must I do so that $key match something but not an empty
value/string?
(7) I read Bob's expression of $key =~ /^$cid$/ as :- look for a string $cid
and that the line-of-input must only contain the string $cid.
Given $key = 1234; and $cid = '';
Bob's expression of $key =~ /^$cid$/ do not match.
However, based on Andrea's explanation (which I could have misread him) in
para(5),
the expression $key =~ /^$cid$/ should match an empty string too. I say so
because (based on Andrea's explanation) $key has an equivalent of \b1234\b
and if \b is equivalent to an empty string.
And if \b is not equivalent to an empty string, then this expression $key =~
/$cid/ or $key =~ /\b$cid\b/ should not match an empty string which it
does.
By the way, I noted that without the border \b,
$key =~ /$cid/; ## match an empty string too and I could understand the
reason based on Andrea's explanation.
> So of course, where one word boundary is,
> there are two or three or million ones.
> (They all have a length of 0)
>
> Greetings,
> Andrea
All help and explanations appreciated.
Thank You.
--- end of msg ---- my original post below -----
----- Original Message -----
From: "Bob Showalter" <[EMAIL PROTECTED]>
To: "'Leon'" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
> > -----Original Message-----
> > From: Leon [mailto:[EMAIL PROTECTED]]
> > Without using $key == $cid,
> > How to construct a pattern so that $key match $cid.
> > I do not understand why in the undermentioned script, $key match $cid.
> > All explanations would be very much appreciated.
> > Thanks
> >
> > use strict;
> > my $cid = '';
> > my $key = '1234';
> > if ($key=~/\b$cid\b/) {
> > print 'true';
> > }else {print 'false'};
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