Problem with reg expression

#I want my script to parse HTML tables such as the one included below:

#!/usr/bin/perl -w
use strict;
use warnings;

my $moggy = '

Re: Problem with reg expression

In our last episode, , the
lovely and talented Peter Jamieson broadcast on comp.lang.perl.misc:

> #I want my script to parse HTML tables such as the one included below:

> #!/usr/bin/perl -w
> use strict;
> use warnings;

> my $moggy = '

Re: Problem with reg expression

Peter Jamieson wrote:
> #I want my script to parse HTML tables such as the one included below:
>
> #!/usr/bin/perl -w
> use strict;
> use warnings;
>
> my $moggy = '

Re: Problem with reg expression

Lars Eighner wrote:
> In our last episode, , the
> lovely and talented Peter Jamieson broadcast on comp.lang.perl.misc:
>>
>> I would have expected
>> $d to be: > 520M, $e to be: ">FINE and $f: to be R">GOOD
>
> Third, what exactly did you think the values of $e and $f would be?

The OP already let us know that, didn't he?

> The assignment ($d,$e,$f) = /TrackCond(.*)<\/TD>/g; is nonsense whether
> you are parsing html or a grocery list.

Why?

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

Re: Problem with reg expression

In our last episode,
<5k6l00F283tnU2@mid.individual.net>,
the lovely and talented Gunnar Hjalmarsson
broadcast on comp.lang.perl.misc:

> Lars Eighner wrote:
>> In our last episode, , the
>> lovely and talented Peter Jamieson broadcast on comp.lang.perl.misc:
>>>
>>> I would have expected
>>> $d to be: > 520M, $e to be: ">FINE and $f: to be R">GOOD
>>
>> Third, what exactly did you think the values of $e and $f would be?

> The OP already let us know that, didn't he?

>> The assignment ($d,$e,$f) = /TrackCond(.*)<\/TD>/g; is nonsense whether
>> you are parsing html or a grocery list.

> Why?

because .* will eat everything that matches (if anything does) so
$e and $f will always be empty (and $d will be empty if there is no match).


--
Lars Eighner
Countdown: 503 days to go.
What do you do when you're debranded?

Re: Problem with reg expression

>> #I want my script to parse HTML tables such as the one included below:
>
>> #!/usr/bin/perl -w
>> use strict;
>> use warnings;
>
>> my $moggy = '

Re: Problem with reg expression

Peter Jamieson wrote:
> ($d,$e,$f) = /TrackCond(.*)<\/TD>/g;
>
> print "d ",$d," e ",$e," f ",$f,"\n";
> I would have expected
> $d to be: > 520M, $e to be: ">FINE and $f: to be R">GOOD
> Can anyone suggest why I don't get this and where I am going wrong here?

All has been said so far (all mysteries solved),
but I'd straighten up the whole thing a little bit:

...
my $moggy = '

Re: Problem with reg expression

Lars Eighner wrote:
> In our last episode,
> <5k6l00F283tnU2@mid.individual.net>,
> the lovely and talented Gunnar Hjalmarsson
> broadcast on comp.lang.perl.misc:
>> Lars Eighner wrote:
>>> The assignment ($d,$e,$f) = /TrackCond(.*)<\/TD>/g; is nonsense whether
>>> you are parsing html or a grocery list.
>>
>> Why?
>
> because .* will eat everything that matches (if anything does) so
> $e and $f will always be empty (and $d will be empty if there is no match).

I thought you had covered the greediness thing in your "Second"
comment... The failure to make .* non-greedy doesn't make the whole
statement "nonsense" IMO.

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

Re: Problem with reg expression

Gunnar Hjalmarsson writes:

> Lars Eighner wrote:
>
>> The assignment ($d,$e,$f) = /TrackCond(.*)<\/TD>/g; is nonsense whether
>> you are parsing html or a grocery list.
>
> Why?

In list context, m// returns the captured subexpressions. There are three
elements in the list being assigned to, but only one captured subexpression
in the regex.

sherm--

--
Web Hosting by West Virginians, for West Virginians: http://wv-www.net
Cocoa programming in Perl: http://camelbones.sourceforge.net

Re: Problem with reg expression

Sherm Pendley writes:

> Gunnar Hjalmarsson writes:
>
>> Lars Eighner wrote:
>>
>>> The assignment ($d,$e,$f) = /TrackCond(.*)<\/TD>/g; is nonsense whether
>>> you are parsing html or a grocery list.
>>
>> Why?
>
> In list context, m// returns the captured subexpressions. There are three
> elements in the list being assigned to, but only one captured subexpression
> in the regex.

Sorry, my bad - I didn't notice the 'g' modifier. That will allow multiple
matches of the subexpression to be captured, and returned as a list.

Note to self: Never post before coffee.

sherm--

--
Web Hosting by West Virginians, for West Virginians: http://wv-www.net
Cocoa programming in Perl: http://camelbones.sourceforge.net

Re: Problem with reg expression

In our last episode, , the lovely and talented
Sherm Pendley broadcast on comp.lang.perl.misc:

> Sherm Pendley writes:

>> Gunnar Hjalmarsson writes:
>>
>>> Lars Eighner wrote:
>>>
>>>> The assignment ($d,$e,$f) = /TrackCond(.*)<\/TD>/g; is nonsense whether
>>>> you are parsing html or a grocery list.
>>>
>>> Why?
>>
>> In list context, m// returns the captured subexpressions. There are three
>> elements in the list being assigned to, but only one captured subexpression
>> in the regex.

> Sorry, my bad - I didn't notice the 'g' modifier. That will allow multiple
> matches of the subexpression to be captured, and returned as a list.

Well, no, you were right the first time, if for the wrong reasons. Because
of .* being unmodified, this kind of expression can never produce more than
one match, not matter how many g's you stick on the end. That is why it is
nonsense: putting a g on the end of something that can match at most once is
nonsense.

Something(.*)anotherthing can produce at most one match. The usual culprit
is the . because it matches just anything. Many times it does not have to
be . and replacing . with a bracketed range will help. In this case, for
example [^<]* has a chance of producing several matches. They would not
necessarily be right because in HTML a different tag could be nested in the
TD element, but you would be right to think there could be more than one
match, so /g would make sense.

> Note to self: Never post before coffee.

--
Lars Eighner
Countdown: 502 days to go.
What do you do when you're debranded?

Re: Problem with reg expression

Lars Eighner wrote:
> Because of .* being unmodified, this kind of expression can never
> produce more than one match, not matter how many g's you stick on
> the end.



> Something(.*)anotherthing can produce at most one match. The usual
> culprit is the . because it matches just anything.

Those statements are not true. Without the /s modifier, the . matches
any character but a newline.

C:\home>type test.pl
my $list = < 1. Milk
2. Sugar
3. Apples
EOL

my @items = $list =~ /\d+\.\s+(.*)/g;

print join(', ', @items), "\n";

C:\home>test.pl
Milk, Sugar, Apples

C:\home>

> Many times it does not have to
> be . and replacing . with a bracketed range will help.

That, OTOH, is true.

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

Re: Problem with reg expression

In our last episode,
<5k8gv4F2ke1oU1@mid.individual.net>,
the lovely and talented Gunnar Hjalmarsson
broadcast on comp.lang.perl.misc:

> Lars Eighner wrote:
>> Because of .* being unmodified, this kind of expression can never
>> produce more than one match, not matter how many g's you stick on
>> the end.

>

>> Something(.*)anotherthing can produce at most one match. The usual
>> culprit is the . because it matches just anything.

> Those statements are not true. Without the /s modifier, the . matches
> any character but a newline.

> C:\home>type test.pl
> my $list = < > 1. Milk
> 2. Sugar
> 3. Apples
> EOL

The OP would not have been in trouble if he had convenient line breaks,
but

#!/usr/local/bin/perl

my $list = < 1. Milk 2. Sugar 3. Apples
EOL

my @items = $list =~ /\d+\.\s+(.*)/g;

foreach $thing (@items){
print "$thing |";
}
print "\n";

yeilds:

Milk 2. Sugar 3. Apples |

or in other words, only one match.


> my @items = $list =~ /\d+\.\s+(.*)/g;

> print join(', ', @items), "\n";

> C:\home>test.pl
> Milk, Sugar, Apples

> C:\home>

>> Many times it does not have to
>> be . and replacing . with a bracketed range will help.

> That, OTOH, is true.

--
Lars Eighner
Countdown: 502 days to go.
What do you do when you're debranded?

Re: Problem with reg expression

"Gunnar Hjalmarsson" wrote in message
news:5k6kqpF283tnU1@mid.individual.net...
> Peter Jamieson wrote:
>> #I want my script to parse HTML tables such as the one included below:
>>
>> #!/usr/bin/perl -w
>> use strict;
>> use warnings;
>>
>> my $moggy = '

Re: Problem with reg expression

"Mirco Wahab" wrote in message
news:fbllc1$19p$1@nserver.hrz.tu-freiberg.de...
> Peter Jamieson wrote:
>> ($d,$e,$f) = /TrackCond(.*)<\/TD>/g;
>>
>> print "d ",$d," e ",$e," f ",$f,"\n";
>> I would have expected
>> $d to be: > 520M, $e to be: ">FINE and $f: to be R">GOOD
>> Can anyone suggest why I don't get this and where I am going wrong here?
>
> All has been said so far (all mysteries solved),
> but I'd straighten up the whole thing a little bit:
>
> ...
> my $moggy = '
>