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Assume I have a regexp, /^(hello)|(goodbye)$/ for example.

I want to see wether a particular string matches part of that
particular regexp, so "", "h", "he", "hel", "hell", "hello", "g",
"go", "goo" "good", "goodb", "goodby" and "goodbye" would be ok,
and anything else wouldn't.

I could hand-craft this example easily enough, but it grows
tedious and error-prone for more general regular expressions,
and automation would be much preferred.

Ideas?

Thomas Koenig wrote:
> Assume I have a regexp, /^(hello)|(goodbye)$/ for example.
>
> I want to see wether a particular string matches part of that
> particular regexp, so "", "h", "he", "hel", "hell", "hello", "g",
> "go", "goo" "good", "goodb", "goodby" and "goodbye" would be ok,
> and anything else wouldn't.
>
> I could hand-craft this example easily enough, but it grows
> tedious and error-prone for more general regular expressions,
> and automation would be much preferred.
>
> Ideas?

Take a look at the source of File::Stream. A very similar problem is
solved in File::Stream::find and the solution to that problem could
probably be easily be adapted (simplified!) to solve your problem.

"Thomas Koenig" <> wrote in message
news:cettfn$4o9$...
> Assume I have a regexp, /^(hello)|(goodbye)$/ for example.
>
> I want to see wether a particular string matches part of that
> particular regexp, so "", "h", "he", "hel", "hell", "hello", "g",
> "go", "goo" "good", "goodb", "goodby" and "goodbye" would be ok,
> and anything else wouldn't.
>
> I could hand-craft this example easily enough, but it grows
> tedious and error-prone for more general regular expressions,
> and automation would be much preferred.
>
> Ideas?

Something like:

if(test($input,"hello") || test($input,"goodbye"))
{
# stuff
}

sub test
{
my($s1,$s2)=@_;
for my $len(0..length($s2))
{
return 1 if(substr($s2,0,$len) eq $s1);
}
return 0;
}

In article <cettfn$4o9$>,
Thomas Koenig <> wrote:
>Assume I have a regexp, /^(hello)|(goodbye)$/ for example.
>
>I want to see wether a particular string matches part of that
>particular regexp, so "", "h", "he", "hel", "hell", "hello", "g",
>"go", "goo" "good", "goodb", "goodby" and "goodbye" would be ok,
>and anything else wouldn't.
>
>I could hand-craft this example easily enough, but it grows
>tedious and error-prone for more general regular expressions,
>and automation would be much preferred.
>
>Ideas?

Sounds as if 'index' (perldoc -f index) might be easier and
in some cases faster than a regex:


my $substring = ...
for ( qw/hello goodbye/ ) {
print "$substring matched $_\n" if index($_, $substring) != -1;
}

--
Charles DeRykus

Thomas Koenig <> wrote:

: Assume I have a regexp, /^(hello)|(goodbye)$/ for example.
:
: I want to see wether a particular string matches part of that
: particular regexp, so "", "h", "he", "hel", "hell", "hello", "g",
: "go", "goo" "good", "goodb", "goodby" and "goodbye" would be ok,
: and anything else wouldn't.
:
: I could hand-craft this example easily enough, but it grows
: tedious and error-prone for more general regular expressions,
: and automation would be much preferred.

This sounds like an opportunity to abuse Perl's
(?(condition)pattern) regex feature.

#!/perl
use strict;
use warnings;

my $pat_h = buildpattern( 'hello' );
my $pat_g = buildpattern( 'goodbye' );

while(<DATA> ) {
chomp;
print "matched '$1' in '$_'\n"
if /$pat_h/ or /$pat_g/;
}

sub buildpattern {
my @lets = $_[0] =~ /./g;
my $pat;
for( 0 .. $#lets ) {
$pat .= $_ == 0 ? $lets[$_] :
$_ == 1 ? "($lets[$_])?" :
"((?($_)$lets[$_]))?"
}
return qr/(^$pat)/;
}

__DATA__
hello
helpme
haveaniceday
goodbye
goodgrief
gabbagabbahey

Brian McCauley <> wrote:

>> Assume I have a regexp, /^(hello)|(goodbye)$/ for example.
>>
>> I want to see wether a particular string matches part of that
>> particular regexp,

>Take a look at the source of File::Stream. A very similar problem is
>solved in File::Stream::find and the solution to that problem could
>probably be easily be adapted (simplified!) to solve your problem.

I'm currently doing that, and trying to understand what YAPE::regexp
does (which isn't too easy

If I get anywhere, I'll let the newsgroup know.

On Mon, 9 Aug 2004, Thomas Koenig wrote:

>Brian McCauley <> wrote:
>
>>> Assume I have a regexp, /^(hello)|(goodbye)$/ for example.
>>>
>>> I want to see wether a particular string matches part of that
>>> particular regexp,
>
>>Take a look at the source of File::Stream. A very similar problem is
>>solved in File::Stream::find and the solution to that problem could
>>probably be easily be adapted (simplified!) to solve your problem.
>
>I'm currently doing that, and trying to understand what YAPE::regexp
>does (which isn't too easy

I'd suggest switching over to Regexp:arser. I'm hoping to get
Regexp::Explain out in the near future.

--
Jeff "japhy" Pinyan % How can we ever be the sold short or
RPI Acacia Brother #734 % the cheated, we who for every service
RPI Corporation Secretary % have long ago been overpaid?
http://japhy.perlmonk.org/ %
http://www.perlmonks.org/ % -- Meister Eckhart

"Andrew Palmer" <> wrote in message
news:HpCQc.3093$...
>
> "Thomas Koenig" <> wrote in message
> news:cettfn$4o9$...
> > Assume I have a regexp, /^(hello)|(goodbye)$/ for example.
> >
> > I want to see wether a particular string matches part of that
> > particular regexp, so "", "h", "he", "hel", "hell", "hello", "g",
> > "go", "goo" "good", "goodb", "goodby" and "goodbye" would be ok,
> > and anything else wouldn't.
> >
> > I could hand-craft this example easily enough, but it grows
> > tedious and error-prone for more general regular expressions,
> > and automation would be much preferred.
> >
> > Ideas?
>
> Something like:
>
> if(test($input,"hello") || test($input,"goodbye"))
> {
> # stuff
> }
>
> sub test
> {
> my($s1,$s2)=@_;
> for my $len(0..length($s2))
> {
> return 1 if(substr($s2,0,$len) eq $s1);
> }
> return 0;
> }
>

Clearly the above code is retarded. The equivalent using index() is simply:

if(index("hello",$input)==0 || index("goodbye",$input)==0)
{
# stuff
}

The regex tokenizing modules seem unnecessary for the example you posted. Is
your actual test significantly more complicated?