[22170] in Perl-Users-Digest
Perl-Users Digest, Issue: 4391 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Sun Jan 12 18:10:37 2003
Date: Sun, 12 Jan 2003 15:10:10 -0800 (PST)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Sun, 12 Jan 2003 Volume: 10 Number: 4391
Today's topics:
Re: Match-time code evaluation (Ben Morrow)
Re: Match-time code evaluation (Jay Tilton)
Re: Match-time code evaluation (Tad McClellan)
Re: Net::Mysql - capture error messages (Mike Solomon)
Newbie / cgi script doesn't take no option. <estrunk@home.nl>
Re: Newbie / cgi script doesn't take no option. <tony_curtis32@yahoo.com>
Re: Parsing /(terminated|non-terminated)/ records from (Kevin Newman)
reading commandline parameters <nomail@mail.com>
Re: Recreating directory hierarchy <bik.mido@tiscalinet.it>
Re: undef of large Hashes/Arrays took a very long time <pa@panix.com>
Re: Using tr/// - Am I barking up the wrong tree? <Jodyman@hotmail.com>
Re: Using tr/// - Am I barking up the wrong tree? <uri@stemsystems.com>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Sun, 12 Jan 2003 16:29:54 +0000 (UTC)
From: mauzo@mimosa.csv.warwick.ac.uk (Ben Morrow)
Subject: Re: Match-time code evaluation
Message-Id: <avs562$hqa$1@wisteria.csv.warwick.ac.uk>
ramm <invalid@invalid.com> wrote:
>Hello everybody,
> I am reading chapter 5 of "Programming Perl 3rd" and I am
>stuck on this example:
A pageref would have been helpful It's on p211.
>$_ = 'lothlorien';
>m/ (?{ $i = 0 })
> (. (?{ $i++ }) )*
> lori
> /x;
>
>I cannot see why "i" holds 10 after this code is executed. Doesn't
^
$i please. Otherwise you'll get confused when you start with @i, etc.
>backtracking decrease "i" each time a character is given back?
No, it doesn't. Because the code in (?{}) is arbitrary, Perl has no way of
knowing how to reverse it's effects, so it doesn't try. So $i gets up to 10
and never comes back down.
The next paragraph explains how to use local to actually count the chars
matched, if you need to.
>I played around with the code, and ended up with the following:
>
>$_ = 'lothlorien';
>m/ (?{ $i = 0 })
> .*
> (?{ $i++ })
> lori
> /x;
>
>Why does this yield a different result (=1)?
Uh? I get 7...
First (?{ $i = 0 }) matches at the start of the string.
Then .* gobbles 10 characters.
Then (?{ $i++ }) matches nothing.
Then 'l' doesn't match '', so we backtrack and steal a char from .*.
(?{ $i++ }) matches nothing again.
'l' doesn't match 'n', so we backtrack.
(?{ $i++ }).
'l' doesn't match 'en', backtrack.
(?{ $i++ }).
'l' doesn't match 'ien', backtrack.
(?{ $i++ }).
'l' !~ 'rien', backtrack.
(?{ $i++ }).
'l' !~ 'orien', backtrack.
(?{ $i++ }).
'lori' does match 'lorien', so we're done.
That makes $i == 7.
Ben
------------------------------
Date: Sun, 12 Jan 2003 16:57:57 GMT
From: tiltonj@erols.com (Jay Tilton)
Subject: Re: Match-time code evaluation
Message-Id: <3e219a8f.222083858@news.erols.com>
mauzo@mimosa.csv.warwick.ac.uk (Ben Morrow) wrote:
: ramm <invalid@invalid.com> wrote:
:
: >I played around with the code, and ended up with the following:
: >
: >$_ = 'lothlorien';
: >m/ (?{ $i = 0 })
: > .*
: > (?{ $i++ })
: > lori
: > /x;
: >
: >Why does this yield a different result (=1)?
:
: Uh? I get 7...
Different versions of Perl. 5.6 vs 5.8, probably.
------------------------------
Date: Sun, 12 Jan 2003 10:56:55 -0600
From: tadmc@augustmail.com (Tad McClellan)
Subject: Re: Match-time code evaluation
Message-Id: <slrnb237im.9je.tadmc@magna.augustmail.com>
ramm <invalid@invalid.com> wrote:
> I am reading chapter 5 of "Programming Perl 3rd"
That is a awfully big book...
> and I am
> stuck on this example:
... so a page number would have been helpful. (p211)
> $_ = 'lothlorien';
> m/ (?{ $i = 0 })
> (. (?{ $i++ }) )*
> lori
> /x;
>
> I cannot see why "i" holds 10 after this code is executed. Doesn't
> backtracking decrease "i" each time a character is given back?
Obviously not. :-)
You seem to be expecting that perl can "invert/undo" the code
somehow. That might seem a reasonable expectation in the case
of a simple increment, but it wouldn't generalize for something
like (?{ big_ol_subroutine() }).
big_ol_subroutine() might write something to a file for instance.
We can't really expect perl to unwrite what has been written.
> I played around with the code, and ended up with the following:
>
> $_ = 'lothlorien';
> m/ (?{ $i = 0 })
> .*
> (?{ $i++ })
> lori
> /x;
>
> Why does this yield a different result (=1)?
I don't know (yet). Let's try and find out.
As with "all things regex" we turn to "Mastering Regular Expressions"
(2e) for help. :-)
Let's add some stategically placed print()s for debugging, as
suggested on page 332.
--------------------------------------------
#!/usr/bin/perl
#use strict;
use warnings;
$_ = 'lothlorien';
### 1) CODE inside, greedy
m/ (?{ $i = 0 })
(.
(?{ $i++; print "[$`<$&>$'] (i=$i)\n" })
)*
lori
(?{ print "final: [$`<$&>$'] (i=$i)\n\n" })
/x;
### 2) CODE outside, greedy
m/ (?{ $i = 0 })
(.
)*
(?{ $i++; print "[$`<$&>$'] (i=$i)\n" })
lori
(?{ print "final: [$`<$&>$'] (i=$i)\n\n" })
/x;
### 3) CODE inside, non-greedy
m/ (?{ $i = 0 })
(.
(?{ $i++; print "[$`<$&>$'] (i=$i)\n" })
)*?
lori
(?{ print "final: [$`<$&>$'] (i=$i)\n\n" })
/x;
### 4) CODE outside, non-greedy
m/ (?{ $i = 0 })
(.
)*?
(?{ $i++; print "[$`<$&>$'] (i=$i)\n" })
lori
(?{ print "final: [$`<$&>$'] (i=$i)\n\n" })
/x;
--------------------------------------------
output:
[<l>othlorien] (i=1)
[<lo>thlorien] (i=2)
[<lot>hlorien] (i=3)
[<loth>lorien] (i=4)
[<lothl>orien] (i=5)
[<lothlo>rien] (i=6)
[<lothlor>ien] (i=7)
[<lothlori>en] (i=8)
[<lothlorie>n] (i=9)
[<lothlorien>] (i=10)
final: [<lothlori>en] (i=10)
[<loth>lorien] (i=1)
final: [<lothlori>en] (i=1)
[<l>othlorien] (i=1)
[<lo>thlorien] (i=2)
[<lot>hlorien] (i=3)
[<loth>lorien] (i=4)
final: [<lothlori>en] (i=4)
[<>lothlorien] (i=1)
[<loth>lorien] (i=2)
final: [<lothlori>en] (i=2)
I think the regex engine is doing the "Pre-check of required
character/substring optimization" (MRE p244) because the
"lori" substring is required by the pattern.
--
Tad McClellan SGML consulting
tadmc@augustmail.com Perl programming
Fort Worth, Texas
------------------------------
Date: 12 Jan 2003 13:47:06 -0800
From: mike_solomon@lineone.net (Mike Solomon)
Subject: Re: Net::Mysql - capture error messages
Message-Id: <56568be5.0301121347.6ab0938a@posting.google.com>
"Andrey Tapkin" <tapkin@rol.ru> wrote in message news:<avndc2$nal$1@news.sovam.com>...
> Use MysqlPP instead of Mysql:
> ...DBI->connect("DBI:mysqlPP:database...
> Don't close ur eyes when you write something :-))
>
Andrew,
Thanks
I will try and keep my eyes open in future
Regards
Mike
------------------------------
Date: Sun, 12 Jan 2003 17:50:41 +0100
From: "estrunk" <estrunk@home.nl>
Subject: Newbie / cgi script doesn't take no option.
Message-Id: <K0hU9.18956$J6.1762249@zwoll1.home.nl>
Hello all,
I'm realy new to this, and i found an older script to be usefull with my
site.
Now it works but it gives always te line if [ "$FOUND" = = "no" ]; then
echo "<H3>No names found!</H3>"
I know that it defould but if found it should be "yes"
So it shows a lot of information AND a line witch tells me that nothing has
been found.
Please help!!
and please sent it also to my normal e-mailadress as a cc.
-----------script--------------
FOUND="no"
cd $DOCROOT
$GREP -i $VALUE *.* |
$AWK -F':' ' \
$1 == prev { \
print($2) \
}; \
$1 != prev { \
print("</PRE><P><B>Bestandsnaam:</B><BR><I>",$1,"</I>\n<PRE>"); \
print("</PRE><BR><PRE>"); \
print($2); \
FOUND="yes"; \
prev = $1 \
}';
if [ "$FOUND" = = "no" ]; then
echo "<H3>No names found!</H3>"
fi
echo "</BODY></HTML>"
-------------end script---------------
--
Kind Regards,
Met Vriendelijke Groeten,
E. Strunk
------------------------------
Date: Sun, 12 Jan 2003 10:53:29 -0600
From: Tony Curtis <tony_curtis32@yahoo.com>
Subject: Re: Newbie / cgi script doesn't take no option.
Message-Id: <87lm1qs41i.fsf@limey.hpcc.uh.edu>
>> On Sun, 12 Jan 2003 17:50:41 +0100,
>> "estrunk" <estrunk@home.nl> said:
> Hello all, I'm realy new to this, and i found an older
> script to be usefull with my site. Now it works but it
> gives always te line if [ "$FOUND" = = "no" ]; then echo
> "<H3>No names found!</H3>" I know that it defould but if
> found it should be "yes" So it shows a lot of
> information AND a line witch tells me that nothing has
> been found.
> -----------script--------------
> FOUND="no" cd $DOCROOT
That is a shell script.
This is comp.lang.perl.misc.
hth
t
------------------------------
Date: 12 Jan 2003 14:04:36 -0800
From: knewman00@earthlink.net (Kevin Newman)
Subject: Re: Parsing /(terminated|non-terminated)/ records from a file
Message-Id: <4c8e4398.0301121404.5894d065@posting.google.com>
"Jodyman" <Jodyman@hotmail.com> wrote in message news:<PaZT9.5021$Qr4.486776@newsread1.prod.itd.earthlink.net>...
> If the files aren't too large, you can slurp them into a single
> variable and then break up the individual records or fields (i.e. apply
> rules) after having removed all \r\n|\n|\r. I've used this to parse phone
> books before and it works great. I'm not telling you how to do it but
> perhaps a different method.
It's okay, you can tell me how to do it. This problem has challenged
my Perl Kung Fu, so I'm seeking any help I can get. :-)
Good suggestion, but there are a couple of immediate problems that
arise.
1. The size of the files that I work with is routinely in the
100MB-500MB range. On occasion, the files are > 1GB. That might be
okay for one user, but multiple users on the same system may use this
utility.
2. Files with logical record lengths are a very difficult problem
because the logical length often does not agree with the physical
length. So, I would be unable to determine the start and end of each
record unless each record is perfectly formed.
However, if you have an example of what you are describing I would
like to see it. I'm sure there is an "easy" way to handle this data
transparently,
Thanks,
kln
------------------------------
Date: Sun, 12 Jan 2003 22:37:55 GMT
From: Tommi <nomail@mail.com>
Subject: reading commandline parameters
Message-Id: <77mU9.648$0m4.142@read3.inet.fi>
How can I read commandline parameters?
------------------------------
Date: Sun, 12 Jan 2003 19:28:01 +0100
From: Michele Dondi <bik.mido@tiscalinet.it>
Subject: Re: Recreating directory hierarchy
Message-Id: <8gb32v4rntkc82l8ps9ia5t50dgb70991g@4ax.com>
On Thu, 09 Jan 2003 22:47:44 +0100, I (Michele Dondi)
<bik.mido@tiscalinet.it> wrote:
>On Wed, 08 Jan 2003 18:39:20 -0500, Benjamin Goldberg
><goldbb2@earthlink.net> wrote:
>>I suppose... you want to provide some modified code?
[...]
> warn("'$dest' exists: refusing to clobber it"), return if -e $dest;
>I was just about to send this post when I realized, on a second
>thought, that if '-e $dest' and $_ is not the toplevel (source) dir,
[...]
>But maybe I'm missing something obvious and all this is utter
>nonsense...
On a third thought I realized that my second thought was indeed utter
nonsense! This is probably why you didn't even mind following-up. OTOH
I want to acknowledge my gross and embarassing mistake - memento to
myself: never follow-up to Benjamin Goldberg (or anybody) without
thinking at least three times!! :-)
However the first remark still partly applies, only I realize that the
modification I suggested is more annoying than useful with dirs, but I
guess that discussing about this doesn't make any sense any more.
Michele
--
>It's because the universe was programmed in C++.
No, no, it was programmed in Forth. See Genesis 1:12:
"And the earth brought Forth ..."
- Robert Israel on sci.math, thread "Why numbers?"
------------------------------
Date: Sun, 12 Jan 2003 17:16:09 +0000 (UTC)
From: Pierre Asselin <pa@panix.com>
Subject: Re: undef of large Hashes/Arrays took a very long time
Message-Id: <avs7sm$8bk$2@reader1.panix.com>
In <3E20B47D.56246AB6@earthlink.net> Benjamin Goldberg <goldbb2@earthlink.net> writes:
>Why are you undefing, instead of declaring the array as a lexical
>variable and merely letting it go out of scope? Or assigning an empty
>list to it?
I no longer have the script. I don't remember if I undef'd the stuff
or assigned empties. The data structures were at (main) mackage
scope. I know that one version of the script did *nothing* to reclaim
memory, and it took forever to exit after it was done (confirmed by
unbufferred prints).
>When you undef() an array or hash, you're doing something very special,
>which often has bad consequences on performance.
Ok, so the OP should try assigning () and see if that helps.
------------------------------
Date: Sun, 12 Jan 2003 18:40:32 GMT
From: "Jodyman" <Jodyman@hotmail.com>
Subject: Re: Using tr/// - Am I barking up the wrong tree?
Message-Id: <AEiU9.6101$Dq.654277@newsread2.prod.itd.earthlink.net>
"Uri Guttman" <uri@stemsystems.com> wrote in message
> >>>>> "J" == Jodyman <Jodyman@hotmail.com> writes:
>
> J> "R. Charles Henry" <trapforcannedmeatproduct@hotmail.com> wrote in
message
>
> >> Trying to convert individual letters in a string, to gif image HTML
tags:
> >> e.g.
> >> from: jo@jo.com to <img src="j.gif"><img src="o.gif"><img
> J> src="at.gif"><img src="j.gif"> etc.
> >> is there an easier way of doing this?
>
> J> my $in = 'jo@jo.com';
>
> J> my @in = split //, $in;
>
> J> foreach (@in) {
> J> $html .= "<img src='$_.gif'>";
> J> }
>
> J> print $html;
>
> why the split and loop? a simple s/// will do it.
>
> J> BTW, ..gif, @.gif etc are valid filenames so you can use the easier
way.
>
> but / is not a valid filename in unix, : is not in macos.
>
> to handle special chars, you make a hash. you also can handle alpha
> chars in there.
>
> my %char2file = (
> '@' => 'at',
> '#' => 'hash',
> map { $_ => $_ } 'a' .. 'z' ) ;
>
> my $html = 'jo@jo.com';
> $html =~ s/(.)/<img src="$char2hash{$1}.gif">/g ;
### slight embellishment:
#!c:\perl\bin\perl -w
use strict;
my %char2file = (
'@' => 'at',
'#' => 'hash',
map { $_ => $_ } 'a' .. 'z' ) ;
my $html = 'jo@jo.com';
$html =~ s/(.)/<img src="$char2hash{$1}.gif">/g ;
Global symbol "%char2hash" requires explicit package name at mapchar.pl line
10.
Execution of mapchar.pl aborted due to compilation errors.
Seems this code is broken. ;-)
Jody
------------------------------
Date: Sun, 12 Jan 2003 19:13:55 GMT
From: Uri Guttman <uri@stemsystems.com>
Subject: Re: Using tr/// - Am I barking up the wrong tree?
Message-Id: <x71y3idvv1.fsf@mail.sysarch.com>
>>>>> "J" == Jodyman <Jodyman@hotmail.com> writes:
J> "Uri Guttman" <uri@stemsystems.com> wrote in message
>>
>> my %char2file = (
>> $html =~ s/(.)/<img src="$char2hash{$1}.gif">/g ;
J> Global symbol "%char2hash" requires explicit package name at
J> mapchar.pl line
J> Seems this code is broken. ;-)
i didn't claim it was tested. a simple name mistake caught by the use of
strict. so it is a good example to those who don't use strict. i don't
even count that as a bug as it is trivial to find and fix.
uri
--
Uri Guttman ------ uri@stemsystems.com -------- http://www.stemsystems.com
----- Stem and Perl Development, Systems Architecture, Design and Coding ----
Search or Offer Perl Jobs ---------------------------- http://jobs.perl.org
Damian Conway Perl Classes - January 2003 -- http://www.stemsystems.com/class
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
From: Perl-Users-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 6 Apr 01)
Message-Id: <null>
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------------------------------
End of Perl-Users Digest V10 Issue 4391
***************************************
