[31878] in Perl-Users-Digest
Perl-Users Digest, Issue: 3141 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Fri Sep 24 06:09:21 2010
Date: Fri, 24 Sep 2010 03:09:06 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Fri, 24 Sep 2010 Volume: 11 Number: 3141
Today's topics:
Re: FAQ 1.14 What is a JAPH? <brian.d.foy@gmail.com>
Re: FAQ 4.8 How do I perform an operation on a series o <brian.d.foy@gmail.com>
Need Regex for phone number <ernesto@ernestoreyes.com>
Re: Need Regex for phone number <ben@morrow.me.uk>
Re: Need Regex for phone number <tadmc@seesig.invalid>
Re: Need Regex for phone number <kst-u@mib.org>
Re: Need Regex for phone number <uri@StemSystems.com>
Re: Need Regex for phone number <tch@nospam.wpkg.org>
Re: Need Regex for phone number (Randal L. Schwartz)
Re: perlop doc: Regexp Quote-Like Operators error? <brian.d.foy@gmail.com>
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@seesig.invalid
Re: Removing tag + closing tag (David Canzi)
Re: Removing tag + closing tag <ben@morrow.me.uk>
Re: Removing tag + closing tag sln@netherlands.com
Re: Removing tag + closing tag <derykus@gmail.com>
Re: Removing tag + closing tag <jurgenex@hotmail.com>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Thu, 23 Sep 2010 18:25:19 -0700
From: brian d foy <brian.d.foy@gmail.com>
Subject: Re: FAQ 1.14 What is a JAPH?
Message-Id: <230920101825193743%brian.d.foy@gmail.com>
In article <867higfp59.fsf@red.stonehenge.com>, Randal L. Schwartz
<merlyn@stonehenge.com> wrote:
> >>>>> "PerlFAQ" == PerlFAQ Server <brian@theperlreview.com> writes:
> PerlFAQ> 1.14: What is a JAPH?
>
> Hmm. This makes it sound like *I* never obfuscated mine.
So, how do you want me to change it? What would accurately reflect
reality?
------------------------------
Date: Thu, 23 Sep 2010 18:38:10 -0700
From: brian d foy <brian.d.foy@gmail.com>
Subject: Re: FAQ 4.8 How do I perform an operation on a series of integers?
Message-Id: <230920101838100894%brian.d.foy@gmail.com>
In article <i79cmm$d8k$1@rumours.uwaterloo.ca>, David Canzi
<dmcanzi@remulak.uwaterloo.ca> wrote:
> In article <75Wlo.61884$y85.61853@newsfe13.iad>,
> PerlFAQ Server <brian@theperlreview.com> wrote:
> > for ($i=5; $i < 500_005; $i++) {
> > for my $i (5 .. 500_005) {
>
> Should be: for my $i (5 .. 500_004) {
Fixed, although I made the fix up in the for() so the same numbers were
in each example.
Thanks,
------------------------------
Date: Thu, 23 Sep 2010 12:19:38 -0700 (PDT)
From: lotug <ernesto@ernestoreyes.com>
Subject: Need Regex for phone number
Message-Id: <a145d200-a6c6-49f2-bb50-138012bce910@a30g2000vbt.googlegroups.com>
I need Regex to indentify 3108222400 phone number.
------------------------------
Date: Thu, 23 Sep 2010 21:11:30 +0100
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: Need Regex for phone number
Message-Id: <isosm7-6g.ln1@osiris.mauzo.dyndns.org>
Quoth lotug <ernesto@ernestoreyes.com>:
> I need Regex to indentify 3108222400 phone number.
/^3108222400$/
Ben
------------------------------
Date: Thu, 23 Sep 2010 16:05:51 -0500
From: Tad McClellan <tadmc@seesig.invalid>
Subject: Re: Need Regex for phone number
Message-Id: <slrni9ng9m.clt.tadmc@tadbox.sbcglobal.net>
lotug <ernesto@ernestoreyes.com> wrote:
> I need Regex to indentify 3108222400 phone number.
No you don't, a simple equality test will suffice for that:
$phone_number eq '3108222400';
The quality of the answers you receive here is in direct
proportion to the quality of the questions you post here...
Have you seen the Posting Guidelines that are posted here frequently?
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.liamg\100cm.j.dat/"
The above message is a Usenet post.
I don't recall having given anyone permission to use it on a Web site.
------------------------------
Date: Thu, 23 Sep 2010 14:07:27 -0700
From: Keith Thompson <kst-u@mib.org>
Subject: Re: Need Regex for phone number
Message-Id: <lneickb240.fsf@nuthaus.mib.org>
lotug <ernesto@ernestoreyes.com> writes:
> I need Regex to indentify 3108222400 phone number.
my $num = "3108222400";
if ($num =~ /^3108222400$/) {
print "Yes, it's a phone number\n";
}
Now what did you really want to ask? Do you need to recognize
international numbers, or just numbers within the NANP? Is the area
code required? Can the area code be surrounded by parentheses? Can
you have spaces between digits? Hyphens? Periods? Can non-digit
characters, if any, be placed arbitrarily, or must they reflect
the structure of the number? Is a leading "1" allowed? What about
"+1"? What about extensions? What about textual representations
like 1-800-FLOWERS?
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
------------------------------
Date: Thu, 23 Sep 2010 17:16:25 -0400
From: "Uri Guttman" <uri@StemSystems.com>
Subject: Re: Need Regex for phone number
Message-Id: <87mxr8qhxy.fsf@quad.sysarch.com>
>>>>> "KT" == Keith Thompson <kst-u@mib.org> writes:
KT> lotug <ernesto@ernestoreyes.com> writes:
>> I need Regex to indentify 3108222400 phone number.
KT> my $num = "3108222400";
KT> if ($num =~ /^3108222400$/) {
KT> print "Yes, it's a phone number\n";
KT> }
KT> Now what did you really want to ask? Do you need to recognize
KT> international numbers, or just numbers within the NANP? Is the area
KT> code required? Can the area code be surrounded by parentheses? Can
KT> you have spaces between digits? Hyphens? Periods? Can non-digit
KT> characters, if any, be placed arbitrarily, or must they reflect
KT> the structure of the number? Is a leading "1" allowed? What about
KT> "+1"? What about extensions? What about textual representations
KT> like 1-800-FLOWERS?
if ( m{\QNow what did you really want to ask? Do you need to recognize
international numbers, or just numbers within the NANP? Is the area
code required? Can the area code be surrounded by parentheses? Can
you have spaces between digits? Hyphens? Periods? Can non-digit
characters, if any, be placed arbitrarily, or must they reflect
the structure of the number? Is a leading "1" allowed? What about
"+1"? What about extensions? What about textual representations
like 1-800-FLOWERS?} )
print "Yes, it has phone number like attributes\n" ;
:)
uri
--
Uri Guttman ------ uri@stemsystems.com -------- http://www.sysarch.com --
----- Perl Code Review , Architecture, Development, Training, Support ------
--------- Gourmet Hot Cocoa Mix ---- http://bestfriendscocoa.com ---------
------------------------------
Date: Thu, 23 Sep 2010 23:38:50 +0200
From: Tomasz Chmielewski <tch@nospam.wpkg.org>
Subject: Re: Need Regex for phone number
Message-Id: <8g1vnbF8mbU1@mid.uni-berlin.de>
On 23.09.2010 23:16, Uri Guttman wrote:
(...)
> KT> Now what did you really want to ask? Do you need to recognize
> KT> international numbers, or just numbers within the NANP? Is the area
> KT> code required? Can the area code be surrounded by parentheses? Can
> KT> you have spaces between digits? Hyphens? Periods? Can non-digit
> KT> characters, if any, be placed arbitrarily, or must they reflect
> KT> the structure of the number? Is a leading "1" allowed? What about
> KT> "+1"? What about extensions? What about textual representations
> KT> like 1-800-FLOWERS?
>
> if ( m{\QNow what did you really want to ask? Do you need to recognize
> international numbers, or just numbers within the NANP? Is the area
> code required? Can the area code be surrounded by parentheses? Can
> you have spaces between digits? Hyphens? Periods? Can non-digit
> characters, if any, be placed arbitrarily, or must they reflect
> the structure of the number? Is a leading "1" allowed? What about
> "+1"? What about extensions? What about textual representations
> like 1-800-FLOWERS?} )
>
> print "Yes, it has phone number like attributes\n" ;
>
> :)
Ah, you forgot:
use Phone::Regex qw(3108222400 flowers);
;)
--
Tomasz Chmielewski
http://wpkg.org
------------------------------
Date: Thu, 23 Sep 2010 14:26:17 -0700
From: merlyn@stonehenge.com (Randal L. Schwartz)
Subject: Re: Need Regex for phone number
Message-Id: <86vd5ww3ra.fsf@red.stonehenge.com>
>>>>> "lotug" == lotug <ernesto@ernestoreyes.com> writes:
lotug> I need Regex to indentify 3108222400 phone number.
How far do you want to indent it?
s/^/ /;
will insert four spaces.
:-)
--
Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
<merlyn@stonehenge.com> <URL:http://www.stonehenge.com/merlyn/>
Smalltalk/Perl/Unix consulting, Technical writing, Comedy, etc. etc.
See http://methodsandmessages.vox.com/ for Smalltalk and Seaside discussion
------------------------------
Date: Thu, 23 Sep 2010 18:45:06 -0700
From: brian d foy <brian.d.foy@gmail.com>
Subject: Re: perlop doc: Regexp Quote-Like Operators error?
Message-Id: <230920101845065817%brian.d.foy@gmail.com>
[[ This message was both posted and mailed: see
the "To," "Cc," and "Newsgroups" headers for details. ]]
In article
<850db0ca-65ff-4f46-b73e-7922a51f7806@u13g2000vbo.googlegroups.com>,
ruwolf <rudolf.dovicin@gmail.com> wrote:
> (Sorry, I have sent this message to comp.lang.perl.moderated but no
> response has been returned to me.)
>
> I think I have found an error in perlop documentation.
Fixed in 51622cce.
Thanks,
------------------------------
Date: Fri, 24 Sep 2010 02:09:51 -0500
From: tadmc@seesig.invalid
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
Message-Id: <mu-dnXyvwt4i0wHRnZ2dnUVZ5g6dnZ2d@giganews.com>
Outline
Before posting to comp.lang.perl.misc
Must
- Check the Perl Frequently Asked Questions (FAQ)
- Check the other standard Perl docs (*.pod)
Really Really Should
- Lurk for a while before posting
- Search a Usenet archive
If You Like
- Check Other Resources
Posting to comp.lang.perl.misc
Is there a better place to ask your question?
- Question should be about Perl, not about the application area
How to participate (post) in the clpmisc community
- Carefully choose the contents of your Subject header
- Use an effective followup style
- Speak Perl rather than English, when possible
- Ask perl to help you
- Do not re-type Perl code
- Provide enough information
- Do not provide too much information
- Do not post binaries, HTML, or MIME
Social faux pas to avoid
- Asking a Frequently Asked Question
- Asking a question easily answered by a cursory doc search
- Asking for emailed answers
- Beware of saying "doesn't work"
- Sending a "stealth" Cc copy
Be extra cautious when you get upset
- Count to ten before composing a followup when you are upset
- Count to ten after composing and before posting when you are upset
-----------------------------------------------------------------
Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
This newsgroup, commonly called clpmisc, is a technical newsgroup
intended to be used for discussion of Perl related issues (except job
postings), whether it be comments or questions.
As you would expect, clpmisc discussions are usually very technical in
nature and there are conventions for conduct in technical newsgroups
going somewhat beyond those in non-technical newsgroups.
The article at:
http://www.catb.org/~esr/faqs/smart-questions.html
describes how to get answers from technical people in general.
This article describes things that you should, and should not, do to
increase your chances of getting an answer to your Perl question. It is
available in POD, HTML and plain text formats at:
http://www.rehabitation.com/clpmisc.shtml
For more information about netiquette in general, see the "Netiquette
Guidelines" at:
http://andrew2.andrew.cmu.edu/rfc/rfc1855.html
A note to newsgroup "regulars":
Do not use these guidelines as a "license to flame" or other
meanness. It is possible that a poster is unaware of things
discussed here. Give them the benefit of the doubt, and just
help them learn how to post, rather than assume that they do
know and are being the "bad kind" of Lazy.
A note about technical terms used here:
In this document, we use words like "must" and "should" as
they're used in technical conversation (such as you will
encounter in this newsgroup). When we say that you *must* do
something, we mean that if you don't do that something, then
it's unlikely that you will benefit much from this group.
We're not bossing you around; we're making the point without
lots of words.
Do *NOT* send email to the maintainer of these guidelines. It will be
discarded unread. The guidelines belong to the newsgroup so all
discussion should appear in the newsgroup. I am just the secretary that
writes down the consensus of the group.
Before posting to comp.lang.perl.misc
Must
This section describes things that you *must* do before posting to
clpmisc, in order to maximize your chances of getting meaningful replies
to your inquiry and to avoid getting flamed for being lazy and trying to
have others do your work.
The perl distribution includes documentation that is copied to your hard
drive when you install perl. Also installed is a program for looking
things up in that (and other) documentation named 'perldoc'.
You should either find out where the docs got installed on your system,
or use perldoc to find them for you. Type "perldoc perldoc" to learn how
to use perldoc itself. Type "perldoc perl" to start reading Perl's
standard documentation.
Check the Perl Frequently Asked Questions (FAQ)
Checking the FAQ before posting is required in Big 8 newsgroups in
general, there is nothing clpmisc-specific about this requirement.
You are expected to do this in nearly all newsgroups.
You can use the "-q" switch with perldoc to do a word search of the
questions in the Perl FAQs.
Check the other standard Perl docs (*.pod)
The perl distribution comes with much more documentation than is
available for most other newsgroups, so in clpmisc you should also
see if you can find an answer in the other (non-FAQ) standard docs
before posting.
It is *not* required, or even expected, that you actually *read* all of
Perl's standard docs, only that you spend a few minutes searching them
before posting.
Try doing a word-search in the standard docs for some words/phrases
taken from your problem statement or from your very carefully worded
"Subject:" header.
Really Really Should
This section describes things that you *really should* do before posting
to clpmisc.
Lurk for a while before posting
This is very important and expected in all newsgroups. Lurking means
to monitor a newsgroup for a period to become familiar with local
customs. Each newsgroup has specific customs and rituals. Knowing
these before you participate will help avoid embarrassing social
situations. Consider yourself to be a foreigner at first!
Search a Usenet archive
There are tens of thousands of Perl programmers. It is very likely
that your question has already been asked (and answered). See if you
can find where it has already been answered.
One such searchable archive is:
http://groups.google.com/advanced_search
If You Like
This section describes things that you *can* do before posting to
clpmisc.
Check Other Resources
You may want to check in books or on web sites to see if you can
find the answer to your question.
But you need to consider the source of such information: there are a
lot of very poor Perl books and web sites, and several good ones
too, of course.
Posting to comp.lang.perl.misc
There can be 200 messages in clpmisc in a single day. Nobody is going to
read every article. They must decide somehow which articles they are
going to read, and which they will skip.
Your post is in competition with 199 other posts. You need to "win"
before a person who can help you will even read your question.
These sections describe how you can help keep your article from being
one of the "skipped" ones.
Is there a better place to ask your question?
Question should be about Perl, not about the application area
It can be difficult to separate out where your problem really is,
but you should make a conscious effort to post to the most
applicable newsgroup. That is, after all, where you are the most
likely to find the people who know how to answer your question.
Being able to "partition" a problem is an essential skill for
effectively troubleshooting programming problems. If you don't get
that right, you end up looking for answers in the wrong places.
It should be understood that you may not know that the root of your
problem is not Perl-related (the two most frequent ones are CGI and
Operating System related), so off-topic postings will happen from
time to time. Be gracious when someone helps you find a better place
to ask your question by pointing you to a more applicable newsgroup.
How to participate (post) in the clpmisc community
Carefully choose the contents of your Subject header
You have 40 precious characters of Subject to win out and be one of
the posts that gets read. Don't waste them. Take care while
composing them, they are the key that opens the door to getting an
answer.
Spend them indicating what aspect of Perl others will find if they
should decide to read your article.
Do not spend them indicating "experience level" (guru, newbie...).
Do not spend them pleading (please read, urgent, help!...).
Do not spend them on non-Subjects (Perl question, one-word
Subject...)
For more information on choosing a Subject see "Choosing Good
Subject Lines":
http://www.cpan.org/authors/id/D/DM/DMR/subjects.post
Part of the beauty of newsgroup dynamics, is that you can contribute
to the community with your very first post! If your choice of
Subject leads a fellow Perler to find the thread you are starting,
then even asking a question helps us all.
Use an effective followup style
When composing a followup, quote only enough text to establish the
context for the comments that you will add. Always indicate who
wrote the quoted material. Never quote an entire article. Never
quote a .signature (unless that is what you are commenting on).
Intersperse your comments *following* each section of quoted text to
which they relate. Unappreciated followup styles are referred to as
"top-posting", "Jeopardy" (because the answer comes before the
question), or "TOFU" (Text Over, Fullquote Under).
Reversing the chronology of the dialog makes it much harder to
understand (some folks won't even read it if written in that style).
For more information on quoting style, see:
http://web.presby.edu/~nnqadmin/nnq/nquote.html
Speak Perl rather than English, when possible
Perl is much more precise than natural language. Saying it in Perl
instead will avoid misunderstanding your question or problem.
Do not say: I have variable with "foo\tbar" in it.
Instead say: I have $var = "foo\tbar", or I have $var = 'foo\tbar',
or I have $var = <DATA> (and show the data line).
Ask perl to help you
You can ask perl itself to help you find common programming mistakes
by doing two things: enable warnings (perldoc warnings) and enable
"strict"ures (perldoc strict).
You should not bother the hundreds/thousands of readers of the
newsgroup without first seeing if a machine can help you find your
problem. It is demeaning to be asked to do the work of a machine. It
will annoy the readers of your article.
You can look up any of the messages that perl might issue to find
out what the message means and how to resolve the potential mistake
(perldoc perldiag). If you would like perl to look them up for you,
you can put "use diagnostics;" near the top of your program.
Do not re-type Perl code
Use copy/paste or your editor's "import" function rather than
attempting to type in your code. If you make a typo you will get
followups about your typos instead of about the question you are
trying to get answered.
Provide enough information
If you do the things in this item, you will have an Extremely Good
chance of getting people to try and help you with your problem!
These features are a really big bonus toward your question winning
out over all of the other posts that you are competing with.
First make a short (less than 20-30 lines) and *complete* program
that illustrates the problem you are having. People should be able
to run your program by copy/pasting the code from your article. (You
will find that doing this step very often reveals your problem
directly. Leading to an answer much more quickly and reliably than
posting to Usenet.)
Describe *precisely* the input to your program. Also provide example
input data for your program. If you need to show file input, use the
__DATA__ token (perldata.pod) to provide the file contents inside of
your Perl program.
Show the output (including the verbatim text of any messages) of
your program.
Describe how you want the output to be different from what you are
getting.
If you have no idea at all of how to code up your situation, be sure
to at least describe the 2 things that you *do* know: input and
desired output.
Do not provide too much information
Do not just post your entire program for debugging. Most especially
do not post someone *else's* entire program.
Do not post binaries, HTML, or MIME
clpmisc is a text only newsgroup. If you have images or binaries
that explain your question, put them in a publically accessible
place (like a Web server) and provide a pointer to that location. If
you include code, cut and paste it directly in the message body.
Don't attach anything to the message. Don't post vcards or HTML.
Many people (and even some Usenet servers) will automatically filter
out such messages. Many people will not be able to easily read your
post. Plain text is something everyone can read.
Social faux pas to avoid
The first two below are symptoms of lots of FAQ asking here in clpmisc.
It happens so often that folks will assume that it is happening yet
again. If you have looked but not found, or found but didn't understand
the docs, say so in your article.
Asking a Frequently Asked Question
It should be understood that you may have missed the applicable FAQ
when you checked, which is not a big deal. But if the Frequently
Asked Question is worded similar to your question, folks will assume
that you did not look at all. Don't become indignant at pointers to
the FAQ, particularly if it solves your problem.
Asking a question easily answered by a cursory doc search
If folks think you have not even tried the obvious step of reading
the docs applicable to your problem, they are likely to become
annoyed.
If you are flamed for not checking when you *did* check, then just
shrug it off (and take the answer that you got).
Asking for emailed answers
Emailed answers benefit one person. Posted answers benefit the
entire community. If folks can take the time to answer your
question, then you can take the time to go get the answer in the
same place where you asked the question.
It is OK to ask for a *copy* of the answer to be emailed, but many
will ignore such requests anyway. If you munge your address, you
should never expect (or ask) to get email in response to a Usenet
post.
Ask the question here, get the answer here (maybe).
Beware of saying "doesn't work"
This is a "red flag" phrase. If you find yourself writing that,
pause and see if you can't describe what is not working without
saying "doesn't work". That is, describe how it is not what you
want.
Sending a "stealth" Cc copy
A "stealth Cc" is when you both email and post a reply without
indicating *in the body* that you are doing so.
Be extra cautious when you get upset
Count to ten before composing a followup when you are upset
This is recommended in all Usenet newsgroups. Here in clpmisc, most
flaming sub-threads are not about any feature of Perl at all! They
are most often for what was seen as a breach of netiquette. If you
have lurked for a bit, then you will know what is expected and won't
make such posts in the first place.
But if you get upset, wait a while before writing your followup. I
recommend waiting at least 30 minutes.
Count to ten after composing and before posting when you are upset
After you have written your followup, wait *another* 30 minutes
before committing yourself by posting it. You cannot take it back
once it has been said.
AUTHOR
Tad McClellan and many others on the comp.lang.perl.misc newsgroup.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.liamg\100cm.j.dat/"
The above message is a Usenet post.
I don't recall having given anyone permission to use it on a Web site.
------------------------------
Date: Thu, 23 Sep 2010 16:57:38 +0000 (UTC)
From: dmcanzi@remulak.uwaterloo.ca (David Canzi)
Subject: Re: Removing tag + closing tag
Message-Id: <i7g0u2$h3m$1@rumours.uwaterloo.ca>
In article <d1f9e0b2-ea3d-4f17-aa7f-78aef36fc0b4@m16g2000vbs.googlegroups.com>,
Theo van den Heuvel <tcmvandenheuvel@gmail.com> wrote:
>On 23 sep, 02:24, s...@netherlands.com wrote:
>> On Mon, 20 Sep 2010 18:01:58 -0700 (PDT), jwcarlton
><jwcarl...@gmail.com> wrote:
>> >Let's say I have something like this:
>>
>> >$var = "<font background='#F5F5F5'>Here is some <font
>> >color='#DADADA'>text</font>. Cool, huh?</font>";
>>
>> >I want to remove <font background='#F5F5F5'> and it's matching </
>> >font>, but not the nested font tags.
>>
>> The nesting can be handled via regex recursion (Perl 5.10 and above)
>... Loads of regex madness
>> Done!
>
>The OP is strongly recommended to follow the advice that is posted
>here every week and use an existing HTML parser instead of doing
>something that can be mathematically proven to be impossible unless
>for fairly trivial cases. Sln's approach only indicates how convoluted
>and vulnerable the regex attempts need to be. They can never scale
>when requirements are added.
>
>Theo van den Heuvel
Perl's regular expressions ceased to be regular expressions long
ago and nobody ever got around to coming up with a different name
for them. Perl's regular expressions have grown into a language
within a language which, if not already capable of emulating a
Turing machine, probably soon will be.
Even when people stick to basic features of regular expressions,
ie. features consistent with equivalence to deterministic finite
automata, regular expressions are hard to understand. When it
becomes possible to write large and complex expressions in this
language within a language, the result is as hard to understand
as APL or dc. And whenever this expression has to be examined
again to debug it or improve it, it will have to re-understood.
Every time it needs to be maintained it has to be *solved*.
Today's complex Perl regexp is tomorrow's maintenance headache.
People can impress themselves all they want by being Perl regexp
virtuosi, but they shouldn't do it in public.
--
David Canzi | "If you can't learn to do something well, learn
| to enjoy doing it poorly." -- Ashleigh Brilliant
------------------------------
Date: Thu, 23 Sep 2010 18:56:59 +0100
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: Removing tag + closing tag
Message-Id: <b0hsm7-t513.ln1@osiris.mauzo.dyndns.org>
Quoth dmcanzi@remulak.uwaterloo.ca (David Canzi):
>
> Perl's regular expressions ceased to be regular expressions long
> ago and nobody ever got around to coming up with a different name
> for them. Perl's regular expressions have grown into a language
> within a language which, if not already capable of emulating a
> Turing machine, probably soon will be.
Perl 6 calls them 'rules', and the syntax is capable of expressing full
grammars (I think they're recursive-descent, but I'm not sure). Perl 5
isn't there yet, and since the syntax has to be backwards-compatible
it's necessarily somewhat uglier, but it's getting there.
> Even when people stick to basic features of regular expressions, ie.
> features consistent with equivalence to deterministic finite automata,
> regular expressions are hard to understand. When it becomes possible
> to write large and complex expressions in this language within a
> language, the result is as hard to understand as APL or dc.
This is quite simply false. A piece of code like
my %headers = $str =~ /^ (\w+) : (.*) $/xmg;
is *much* easier to read than the equivalent written out with substr and
index, as well as enormously faster. It *is* necessary to be much more
careful with regular expressions; since the language is even more
compressed than Perl, things like whitespace and layout and braking the
problem into meaningful chunks matter a lot more. I would say that any
pattern with more than about five items in it that doesn't use /x is a
mistake.
> And whenever this expression has to be examined again to debug it or
> improve it, it will have to re-understood.
Uh, that's true of *any* piece of code. That's why it's important to
write code clearly, and write good comments where it's impossible to
write clear code.
> Today's complex Perl regexp is tomorrow's maintenance headache.
Personally I think today's piece of parsing code handwritten in C (or
whatever) is tomorrow's maintenance headache. The various flavours of
declarative text-matching language (regular expressions, yacc grammars,
lex lexers, ...) were invented to *avoid* having to write that code by
hand.
Ben
------------------------------
Date: Thu, 23 Sep 2010 11:17:02 -0700
From: sln@netherlands.com
Subject: Re: Removing tag + closing tag
Message-Id: <hv5n965qdanqd7qit50mkpv8srf5hbq2ns@4ax.com>
On Thu, 23 Sep 2010 16:57:38 +0000 (UTC), dmcanzi@remulak.uwaterloo.ca (David Canzi) wrote:
>Today's complex Perl regexp is tomorrow's maintenance headache.
>
Yet, complex patterns are no more easily handled with other
non-regular expression methods.
Is it time to limit the complexities of life then?
Maybe, take out repetition and variance.
>People can impress themselves all they want by being Perl regexp
>virtuosi, but they shouldn't do it in public.
Why, thank you.
-sln
------------------------------
Date: Thu, 23 Sep 2010 13:55:12 -0700 (PDT)
From: "C.DeRykus" <derykus@gmail.com>
Subject: Re: Removing tag + closing tag
Message-Id: <81f5cae6-589d-46b9-93ab-c83c331b5abe@i17g2000vbq.googlegroups.com>
On Sep 23, 9:57=A0am, dmca...@remulak.uwaterloo.ca (David Canzi) wrote:
> In article <d1f9e0b2-ea3d-4f17-aa7f-78aef36fc...@m16g2000vbs.googlegroups=
.com>,
> Theo van den Heuvel =A0<tcmvandenheu...@gmail.com> wrote:
>
>
>
> >On 23 sep, 02:24, s...@netherlands.com wrote:
> >> On Mon, 20 Sep 2010 18:01:58 -0700 (PDT), jwcarlton
> ><jwcarl...@gmail.com> wrote:
> >> >Let's say I have something like this:
>
> >> >$var =3D "<font background=3D'#F5F5F5'>Here is some <font
> >> >color=3D'#DADADA'>text</font>. Cool, huh?</font>";
>
> >> >I want to remove <font background=3D'#F5F5F5'> and it's matching </
> >> >font>, but not the nested font tags.
>
> >> The nesting can be handled via regex recursion (Perl 5.10 and above)
> >... Loads of regex madness
> >> Done!
>
> >The OP is strongly recommended to follow the advice that is posted
> >here every week and use an existing HTML parser instead of doing
> >something that can be mathematically proven to be impossible unless
> >for fairly trivial cases. Sln's approach only indicates how convoluted
> >and vulnerable the regex attempts need to be. They can never scale
> >when requirements are added.
>
> >Theo van den Heuvel
>
> Perl's regular expressions ceased to be regular expressions long
> ago and nobody ever got around to coming up with a different name
> for them. =A0Perl's regular expressions have grown into a language
> within a language which, if not already capable of emulating a
> Turing machine, probably soon will be.
>
> Even when people stick to basic features of regular expressions,
> ie. features consistent with equivalence to deterministic finite
> automata, regular expressions are hard to understand. =A0When it
> becomes possible to write large and complex expressions in this
> language within a language, the result is as hard to understand
> as APL or dc. =A0And whenever this expression has to be examined
> again to debug it or improve it, it will have to re-understood.
> Every time it needs to be maintained it has to be *solved*.
>
> Today's complex Perl regexp is tomorrow's maintenance headache.
>
> People can impress themselves all they want by being Perl regexp
> virtuosi, but they shouldn't do it in public.
>
I think that's overstated and I especially
disagree with the last sentence. This forum
is for discussing/exploring the Perl language -
capabilities, features, even its quirks. While
a real parser is the right answer, Perl regexes
can now match balanced text - a key part of this
particular task. So a demo is on point and could
be useful in some future problem scenario. It's
fair to be impressed with the power of Perl's
regex capabilities.
Of course, there is considerable complexity to
regexes and they can quickly become unwieldy. But
Perl provides and recommends a way for comment them.
They are not appropriate in every case but they
needn't become maintenance headaches.
--
Charles DeRykus
------------------------------
Date: Thu, 23 Sep 2010 17:50:36 -0700
From: Jürgen Exner <jurgenex@hotmail.com>
Subject: Re: Removing tag + closing tag
Message-Id: <5etn96pdib7e9f2ci3adqlnb88230la5s1@4ax.com>
dmcanzi@remulak.uwaterloo.ca (David Canzi) wrote:
>Perl's regular expressions ceased to be regular expressions long
>ago and nobody ever got around to coming up with a different name
>for them. Perl's regular expressions have grown into a language
>within a language which, if not already capable of emulating a
>Turing machine, probably soon will be.
>
>Even when people stick to basic features of regular expressions,
>ie. features consistent with equivalence to deterministic finite
>automata, regular expressions are hard to understand. When it
>becomes possible to write large and complex expressions in this
>language within a language, the result is as hard to understand
>as APL or dc. And whenever this expression has to be examined
>again to debug it or improve it, it will have to re-understood.
>Every time it needs to be maintained it has to be *solved*.
>
>Today's complex Perl regexp is tomorrow's maintenance headache.
>
>People can impress themselves all they want by being Perl regexp
>virtuosi, but they shouldn't do it in public.
Amen to that!!!
jue
------------------------------
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------------------------------
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