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Meditations is sometimes used as a sounding-board — a place to post initial drafts of perl tutorials, code modules, book reviews, articles, quizzes, etc. — so that the author can benefit from the collective insight of the monks before publishing the finished item to its proper place (be it Tutorials, Cool Uses for Perl, Reviews, or whatever). If you do this, it is generally considered appropriate to prefix your node title with "RFC:" (for "request for comments").
using perl to pull values and files out of virtual spaces
Hello Monks,
I've been using the testing harness of perl to run a download and watermark script, and I've had quite a bit of success with it in testing. As I enter the monastery, I'm getting some false results that I want to explore using perl.
I got back to the literature and used Module::Starter, and now have something that could count as a distro. It's passed 12 rounds of testing, but I've made a big mistake because I backed off of stat'ing the file as an ultimate test of a success. Let me just start with perl as I present Frobnitz.pm:
package Acme::Frobnitz;
use strict;
use warnings;
use IPC::System::Simple qw(capturex);
use Cwd qw(abs_path);
use File::Spec;
use File::stat;
use File::Basename;
use FindBin;
use POSIX qw(strftime);
our $VERSION = '0.03';
That stack of modules just makes me happy to look at, like an xmas tree. And already version 3! IPC::System::Simple is a good choice for a grown-up's version of system() according to haukex's canonical treatment.
The methods wrap calls to bash:
sub new {
my ($class) = @_;
return bless {}, $class;
}
sub _get_script_path {
my ($class, $script_name) = @_; # Resolve base directory dynamical
+ly
my $base_dir = abs_path("$FindBin::Bin/.."); # One level up from b
+in
my $script_path = File::Spec->catfile($base_dir, 'bin', $script_na
+me);
unless (-x $script_path) {
die "Script $script_path does not exist or is not executable.\
+n";
}
return $script_path;
}
sub download {
my ($class, $hyperlink) = @_;
die "No hyperlink provided.\n" unless $hyperlink;
my $script_path = $class->_get_script_path("call_download.sh");
my $output;
eval {
$output = capturex("bash", $script_path, $hyperlink);
};
if ($@) {
die "Error executing $script_path with hyperlink $hyperlink: $
+@\n";
}
return $output;
}
I've been jammed up with version control, because I've been unable to reconstitute my gitlab circumstances (totally my fault). I take snapshots with
tar -czvf Acme-Frobnitz-Snapshot.tar.gz Acme-Frobnitz-Snapshot
They mostly look the same, but I port them back and forth from my mini-mac to a linux machine, with an obligatory-named usb as download target. That happens in the bash part. There's also the docker part and a python part. Much of this source deals with calling one from the other and returning values as well as files. I've wanted perl to "pull the cart" for the whole process, so that I could subject it to testing. LanX rightly laments the dearth of this in contemporaneous culture.
I haven't revealed my screw-up yet...this isn't easy...
I thought I passed the 12th round of testing but later came to realize I was firing blanks as to whether files ended up on the usb drive, and it brings me to a weird moment in testing, where I can use perl to figure out why...
Here's the new perl caller...this is what is "pulling the cart," whatever that means...
use strict;
use warnings;
use Acme::Frobnitz;
my $frobnitz = Acme::Frobnitz->new();
# URL of the video to download
my $video_url = "https://www.instagram.com/p/DDa_FxsNtTe/";
# Step 1: Download the video
my $downloaded_file = $frobnitz->download($video_url);
print "Downloaded video to: $downloaded_file\n";
# Step 2: Verify the downloaded file
print "Verifying downloaded file...\n";
if ($frobnitz->verify_file($downloaded_file)) {
print "File verification successful.\n";
} else {
die "File verification failed. Aborting further processing.\n";
}
# Step 3: Add watermark to the downloaded video
my $final_file = $frobnitz->add_watermark($downloaded_file);
print "Final watermarked video is at: $final_file\n";
I want to make a pure perl test here and use perl to figure out my privileges, and I'm using this. You should note that this is untested software from chatgpt today:
sub verify_file {
my ($class, $file_path) = @_;
die "File path not provided.\n" unless $file_path;
my $abs_path = abs_path($file_path) // $file_path;
if (-e $abs_path) {
print "File exists: $abs_path\n";
# File size
my $size = -s $abs_path;
print "File size: $size bytes\n";
# File permissions
my $permissions = sprintf "%04o", (stat($abs_path)->mode & 077
+77);
print "File permissions: $permissions\n";
# Last modified time
my $mtime = stat($abs_path)->mtime;
print "Last modified: ", strftime("%Y-%m-%d %H:%M:%S", localti
+me($mtime)), "\n";
# Owner and group
my $uid = stat($abs_path)->uid;
my $gid = stat($abs_path)->gid;
print "Owner UID: $uid, Group GID: $gid\n";
return 1; # Verification success
} else {
print "File does not exist: $abs_path\n";
my $dir = dirname($abs_path);
# Report directory details
print "Inspecting directory: $dir\n";
opendir my $dh, $dir or die "Cannot open directory $dir: $!\n"
+;
my @files = readdir $dh;
closedir $dh;
print "Directory contents:\n";
foreach my $file (@files) {
next if $file =~ /^\.\.?\$/; # Skip . and ..
my $file_abs = File::Spec->catfile($dir, $file);
my $type = -d $file_abs ? 'DIR ' : 'FILE';
my $size = -s $file_abs // 'N/A';
print "$type - $file (Size: $size bytes)\n";
}
return 0; # Verification failed
}
}
Let's fire up the debugger, woohoo! This is why I can never leave perl:
(base) fritz@laptop:~/Desktop/Acme-Frobnitz-Snapshot$ perl -d bin/3.d
+river.pl
Loading DB routines from perl5db.pl version 1.55
Editor support available.
Enter h or 'h h' for help, or 'man perldebug' for more help.
main::(bin/3.driver.pl:5): my $frobnitz = Acme::Frobnitz->new();
DB<1>
DB<1> R
+
Warning: some settings and command-line options may be lost!
Loading DB routines from perl5db.pl version 1.55
Editor support available.
Enter h or 'h h' for help, or 'man perldebug' for more help.
main::(bin/3.driver.pl:5): my $frobnitz = Acme::Frobnitz->new();
DB<0> b 16
+
DB<1>
Alright, well I found enough things wrong in there to need to go back and fix. It's funny how you find stuff during the writeup. Without a githost I don't have a means to provide an SSCCE without violating the first S.
For creating the virtual environment with some diagnostics, I've been using this Dockerfile, which has a nice amount of tread on it:
# Start with a base image
FROM python:3.10-slim
# Set PYTHONPATH to include the python_utils directory
ENV PYTHONPATH="/app/lib/python_utils:/app/lib"
# Update apt repository and install necessary dependencies, including
+ffmpeg
RUN apt-get update && \
apt-get install -y --no-install-recommends \
ffmpeg \
python3 \
python3-pip && \
apt-get clean && \
rm -rf /var/lib/apt/lists/*
# Set the working directory
WORKDIR /app
# Copy all files into the Docker image
COPY bin /app/bin
COPY lib /app/lib
COPY conf /app/conf
COPY requirements.txt /app/requirements.txt
COPY Dockerfile /app/Dockerfile
# Install Python dependencies
RUN pip3 install --upgrade pip && pip3 install -r requirements.txt --r
+oot-user-action=ignore
# Debug: List all files in /app and verify the content of lib/python_u
+tils
RUN ls -la /app && ls -la /app/lib && ls -la /app/lib/python_utils
# Debug: Verify requirements.txt is in the container
RUN cat /app/requirements.txt
# Debug: Verify Python environment and MoviePy installation
RUN python3 -c "import sys; print(sys.version)"
RUN python3 -c "import site; print(site.getsitepackages())"
RUN python3 -c "import moviepy; print('MoviePy is correctly installed'
+)"
Docker isn't the easiest thing to get values out of, and this worked. Glad for any critical comments about the code. I gotta figure out how I threw a monkey wrench into what used to work, and I don't find that wrench without gdb. I'm not aware of a python equivalent.
It's that day again, my Monk Day. I'm up to 23 years on this site. Cool!
I had an idea recently that I wanted to scan the log files on the server I run
to catch information about the life-cycle of customer tickets. I've written
various scripts that run under crontab to create and to update a
Freshdesk ticket.
As each of the scripts run, it uses the very handy Log::Log4perl
module to log stuff, and they end up in log files which get rotated (so foo.log
becomes foo.log.1) automatically. How big the files are, and how many backups
you have are all configurable, of course. The logs contain lines like
2024/12/06 06:11:03 INFO : Create FD ticket 427993 for order 663363 ..
+ OK
(The OK at the end is just the result from the API call.) So I could set
up a regexp that would do the usual capture, then add a list of terms that I
should expect, then copy each capture to the variable named in the list .. but
something was telling me there was a cool feature in Perl that I could use. All
of those presentations from YAPC::NA and TPRC were prodding my long-term
memory.
Of course! Named captures! (I wrote about this in Perl's hidden depths). I happily
got the code working, and proudly pasted my clever solution here. And I got
some feedback about how I could simplify my code. And then simplify it some
more .. wow.
Clearly, I am *still* learning Perl, after 25+ years. That's how deep the
language is, and that's how generous the Perl community is with sharing its
knowledge.
"Nobody uses Perl anymore!!" Yeah, well, they should. it's an awesome language.
For a long time, I had a link in my .sig going to Groklaw. I heard that as of December 2024, this link is dead. Still, thanks to PJ for all your work, we owe you so much. RIP Groklaw -- 2003 to 2013.
Recently I got myself a new phone. And, as one does, I installed Termux on it, to have a unix-ish environment for when I need it.
Then, of course, I went to configure Perl and install some modules I'd like there. As this was not my first time doing so, I thought about listing all the modules I want in a cpanfile and then using App::cpanminus to install these, making the process far more reproducible.
But that required some non-Perl prerequisites, like the C compiler, make and perl itself. And of course, also bootstrapping App::cpanminus.
Then I thought a bit on how to combine this setup into a single file. This is what I came up with. It's a cpanfile that doubles as shell script.
#!/bin/bash
# This will install cpanminus and then the Perl modules
# as listed at the end of this script. To run use
# the following commands:
#
# chmod ugo+x ./cpanfile && ./cpanfile
#
eval '
pkg install git perl make clang
if ! cpanm --help 2>&1 >/dev/null ; then
curl -L https://cpanmin.us | perl - App::cpanminus
fi
DIR=$(dirname "$0")
cpanm --installdeps --notest --cpanfile "$DIR"
exit
'
if 0;
requires 'Mojolicious';
requires 'DBIx::Spreadsheet';
#requires 'App::sqldisplay'; # to be released on CPAN
requires 'DBIx::RunSQL';
Greetings from chilly, snowy Buffalo (NY, USA). I spent about 6 years doing no programming at all and now I'm using perl again. I am still hooked on it. So this week I started exploring CPAN modules that give info about and, in some cases, modify, the filesystem. I know of 3 modules that are used for that: the core module File::Spec, the module Path::Class (used it and liked it, a while back), and the module Path::Tiny. This meditation focuses on Path::Tiny, which seems to be stalking me. I see a lot of module authors using it in their code (that is, it has become a common dependency).
Path::Tiny is probably a bit of a misnomer. It has many methods. Many many. What I was most interested in this week was the method tempdir. Something about how tempdir works took me by surprise (yes, I am finally getting around to the point of this meditation :). The method returns a {normalized, right-slashed, absolute} pathname, but it also creates the temporary directory. Maybe I am odd, but I expected to be given a string and then create the directory with that pathname myself!
Below, some code (playful deliberately) that uses tempdir and will demonstrate that when tempdir is called, a directory is created.
#!/usr/bin/env perl
# Last modified: Wed Dec 04 2024 10:48:30 PM -05:00 [EST]
use strict;
use v5.18;
use utf8;
use warnings;
=head1 NAME
pathology.pl
=cut
use Term::ReadKey qw/ReadMode ReadKey/;
use File::Spec;
use Path::Tiny;
my $user;
sub versions
{
say
$File::Spec::VERSION, q[ ]
, $Path::Tiny::VERSION ;
}
sub who
{
no warnings 'deprecated', 'experimental';
use Config;
given (lc( $Config{osname} )) {
when ('linux') { $user = $ENV{USER} }
when ('cygwin') { $user = $ENV{USER} }
when ('mswin32') { $user = $ENV{USERNAME} }
default { say "osname is something we don't know, "
+,
"we'll guess it's something Unixy, so
+" ,
"let's say that user name is " ,
getlogin || "null";
$user = getlogin;
}
}
return $user;
}
# ------------------------------------------------------------- #
# For all its wealth of methods, I found no direct equivalent of
# "tmpdir" in Path::Tiny, so I use File::Spec's.
say "We use " , File::Spec->tmpdir , " for temporary files.";
# ------------------------------------------------------------- #
say "We are currently in directory " , Path::Tiny->cwd;
say "Our filesystem is rooted at " , Path::Tiny->rootdir;
say "Aha, " , who() , ", we may have a temp dir for you!";
my $tadah = Path::Tiny->tempdir(TEMPLATE => "${user}-XXXXXXXX");
say "Maybe we have made a temp directory at " , $tadah , ", let's see:
+";
if ( -e $tadah and -d $tadah ) {
say "'$tadah' already exists and is a directory.";
say "Type 'y' if you wish to remove this directory:";
ReadMode 'cbreak';
my $reply = ReadKey(0);
ReadMode 'normal';
if (lc $reply eq "y") {
print "Ok, we are going to attempt to remove it now ..." ;
rmdir($tadah) and say "Success."
or say "BAH! Could not remove it, reason: $!";
} else {
say "Ok, leaving $tadah alone.";
}
} else {
mkdir($tadah => 0777) and say "created temp dir."
or die "We couldn't make a directory \"$tad
+ah\"", $!;
sleep 6;
rmdir($tadah) and say "$tadah removed."
}
Examine what is said, not who speaks.
Love the truth but pardon error.
Silence betokens consent.
In the absence of evidence, opinion is indistinguishable from prejudice.
So I converted a small string/grammar parser, from pure perl, to XS. And benchmarked it. I was surprised, the old pure perl optree implementation, is only 30% of the speed of XS C code (3/11=%30). A string parser written in C with memcmp() vs PurePerl's eq, 3x slower. Not bad.
More interesting is, I decided as a crazy C/XS guts hack, to have a Perl XSUB, calling another Perl XSUB, C function to C function. And it was FOUR TIMES FASTER. 4x!!!!
Just by getting rid of the PP for() loop and the internal Perl_call_sv() and Perl_pp_entersub() overhead, and totally removing the the Perl 5 engine/API/interpretor, between 2 Perl 5 XSUBs (C functions), it made things FOUR TIMES FASTER.
I'm semi-retired, which means I take care of a client's system of Perl scripts that mostly run without my intervention. I log everything with the excellent Log::Log4perl module, and sometimes I tail those files to keep on eye on the various scripts that run. One group of scripts creates tickets for new orders, and other scripts update these tickets based on what Sage (the accounting system) says.
Eventually, I started to think about understanding the life-cycle of these tickets -- they get created (that's logged in one file), they get updated (logged in a couple of other files), and they get closed (logged in two other files). Could I parse all of the log files and see the life-cycle just by drawing inferences? It's an academic exercise, since all I have to do is query the ticketing system's API about the history of a ticket, but like I said, I'm mostly retired, but I'm still curious.
The lines are like this:
2024/11/28 10:54:04 INFO : Update ticket 425955 to add invoice 802436
+tag .. OK
2024/11/28 10:54:05 INFO : Update ticket 425912 to add invoice 802435
+tag .. OK
2024/11/28 10:54:06 INFO : Add note to ticket 425912 with info about i
+nvoice 802435 .. OK
2024/11/28 10:57:02 INFO : Create FD ticket 425991 for order 662626 ..
+ OK
So I created an AoH data structure with the filename, a useful regular expression, and an action (create or update). (Because for me, it always starts with a data structure to organize the logic.) But then I realized each log file had different elements that needed collecting. How do I handle that without having to write code for each log file? Can't I just add something clever to my data structure?
Eventually, some of my brain cells told me I needed to use a named capture in the regular expressions to handle this. Other brain cells complained that I'd never used that before, but the first group of brain cells said, Nonsense (or Buck Up, I forget), it's all in the Camel if you just look.
So, when you're capturing stuff in a regexp with a clause like (\d+), that first capture just gets stashed in $1. But you can also name that capture (a feature I never needed until now), like this: (?<ticket>\d+). And you get it out by looking at the magic variable %+, so the ticket value is available as $+{ ticket }. SO COOL!
I was then able to write a bunch of regular expressions, all with named captures, and collect whatever I needed from the log lines. Then, if a particular element was there, I would add it to the history hash I was building. So one of the AoH entries looked like this:
{
filename => 'status.log',
regexp => qr/Update (?<ticket>\d+) status to (?<status>.+) \.\./,
action => 'update'
},
I wanted to do all of this in a single statement, rather than have individual if statements for each possible element.
The code runs fine, and does what I expect. Named captures are a very cool feature, but they do exactly what I needed to do. Props to all the smart folks who came up with that idea (and then implemented it). What a cool language.
yesterday I was trying some perl code after neverending boring weeks (workwise..) and I tried to use -s to add rudimentary switch parsing as described here (emphasis added by me):
> -s
enables rudimentary switch parsing for switches on the command line after the program name but before any filename arguments (or before an argument of --).
The above is true when there is a real file containing a perl program:
echo print join ' ', $0, $R > switch-test.pl
# after the program name
perl -s switch-test.pl -R=OK
switch-test.pl OK
# before an argument of --
perl -s switch-test.pl -R=OK --
switch-test.pl OK
# wrong usage
perl -s switch-test.pl -- -R=OK
switch-test.pl
But what if the program is just some code passed with -e (and this is a valid program also for the program name perl's internal value)?
Even with my limited English understanding, I'd suppose something like: perl -s -e "print $R" R=a or perl -s -e -n "print $R" R=a filename (before any filename arguments) but no, it works exactly in the opposite way:
# after the program name
perl -s -e "print join ' ', $0, $R" -R=OK
Unrecognized switch: -R=OK (-h will show valid options).
# before an argument of --
perl -s -e "print join ' ', $0, $R" -R=OK --
Unrecognized switch: -R=OK (-h will show valid options).
# it works in the opposite way of what perlrun states
perl -s -e "print join ' ', $0, $R" -- -R=OK
-e OK
So, given the switch is stated as rudimentary one should expect to use with small oneliners (only our dead pope used it as signature..) and not for serious programs.
In combination with other switches is even unfriendly:
perl -snwe "print join ' ', $0, $R, $/" -- -R=OK lorem.txt
-e OK
-e OK
-e OK
-e OK
I recall recently seeing a remark (on a node I cannot find now) wherein the monk asked "is Cygwin still supported?" That's a good question. Certainly cygwinPerl seem to be alive and current on the Cygwin download servers (at the time of this writing, v5.40.0). But a mechanism for asking questions about Cygwin in general is seemingly problematic and has been for a while. The Cygwin website is completely out of date, directing users to mailing lists that do not exist anymore. Apparently to reach Cygwin developers one must use NNTP (we're talking old school here).
The Cygwin.com site says: "Please note that the gmane website and its newsgroup search interface is down since August 2016. Only the aforementioned NNTP gateway is still up."
I see a fair amount of traffic in Cygwin questions on StackOverflow and its related sites, and if someone were to ask me where to get general help with Cygwin today, that's where I would direct them.
Oct 22, 2024 at 18:07 UTC
Examine what is said, not who speaks.
Love the truth but pardon error.
Silence betokens consent.
In the absence of evidence, opinion is indistinguishable from prejudice.
The Wordpress and Mullenweg story popped up recently, and then just this morning, I read about Perforce and Puppet, where it sounds like Perforce took over the Slack community of Puppet.
The final comment in the Mastodon post was on point:
.. has something happened behind the scenes in tech that I don't know about? Because everybody seems to be acting proper weird lately.
It seems like takeovers for profit (like the IRC kerfuffle a while back -- I can't even remember the old server name) don't work. Are the lawyers taking over? Or is this just Chaos Theory/Entropy throwing us around a bit?
I spent many hours trying to solve a problem, found a solution, and would like to share it in case others might encounter it.
A checkbox that appears on a form on an HTML page has a "name" attribute. Typically it has a "value" attribute. (If there is no "value" attribute, the default is for the web browser to send the string "on", I think, if the user has checked the checkbox before submitting the form.)
Anyway, if it unchecked, naturally there is no value sent to the script that's receiving the submitted form data. Let's say the HTML in the form states that the name of the checkbox is "member." If the user is a member of a certain civic organization, as explained elsewhere on the web page, the web page asks the user to so advise the website owner by checking the checkbox. If not a member, then the user just leaves the checkbox unchecked.
The interesting part is that the script receiving the form data has no idea whether there was a a checkbox named "member" unless the checkbox had been checked by the user. If it was left unchecked, the script doesn't get a "&member=''" (empty string) or even a "&member" in the submitted query string.
Let's say the script uses the submitted data to add the user to a database. Probably a record in a table in a relational database. The script can be written to assume that the person is not to be recorded as a "member" of the civic organization if there is no value coming in for the "member" parameter. If so, the script inserts a record in the table, puts the empty string (or NULL) into the record's "member" field (here, the field in the table happens to be the same as the name of the form parameter), and life is good.
But let's say the new user is indeed a member of the civic organization, and said so by checking the checkbox. So the script stores a "1" in the member field of the new record.
OK. Next step: provide for the editing of the record. We want to have the script create an editing form that looks like the new-user form. The script pulls the user's record from the database, sees there is a value in the member field, and hence the form is created to include "checked=CHECKED" as an attribute, e.g., <input type="checkbox" name="member" checked=CHECKED> is somewhere in the form.
But it's been six months since the user registered as a new user, and during that time she decided to let her membership in the civic organization lapse. So she wants to use the editing screen to update her record -- to literally uncheck the "member" checkbox. She does so, and submits the form.
The script, because it doesn't receive any information about the member checkbox from the user's web browser (see above), has to ASSUME that a parameter named member was in the form, and that the failure to find any submitted value associated with that parameter, or find the parameter in the first place, means the user is wanting to have her record in the database updated so as to replace "1" with "0" (or the empty string, etc.). OK, no big deal. The code is fairly simple.
But what if there were a different form presented to the user. One that is designed to let her change only her username, for example, and doesn't include the "member" checkbox. The HTML in the form is written to submit the data to the same script. But because the script has been written to assume that no incoming data for "member" means the person is no longer a member, then there's trouble when the script updates her record to change the "1" to "0" in the member field. The user only wanted to change her username.
OK, so we revise the script to make no such assumption. Now, though, how will the script know when to change the "member" field from "1" to "0"? It can't assume that every form has given the user a "member" checkbox. This is the assumption that's been made in every code example that I've seen, though.
The solution seems to be to have the form include a hidden input field that lists the names of all of the checkboxes in the form, so the script can safely assume that they're to be treated as having been submitted and they're to be treated as if the user intended them to be unchecked when the form was submitted. This can be done by printing a <input type=hidden value="member"> line somewhere inside the <form ...> and </form> tags.
I used the CGI.pm module to create a form, used its checkbox() function to print a checkbox inside it, and found that, lo and behold, the HTML includes a line that says something like <input type="hidden" name=".cgiparams" value="member"> just before the </form> tag. I had successfully reinvented the wheel.
CGI.pm is then able to redisplay the form (if, for example, the user supplied invalid data in the form such that the script is written to redisplay the form along with an error message), and the stickiness aspect of its created checkboxes means that a checkbox that initially was displayed as being checked will be correctly redisplayed as being unchecked if the user had in fact unchecked the checkbox before submitting the form. CGI.pm apparently knows that the checkbox it creates upon redisplay of the form is not to be checked this time, because it finds the member parameter in the .cgiparams list that was part of the submitted form and it determines that no value came in for the member parameter (or that the parameter didn't come in at all).
My strategy in generating web forms has been to take advantage of CGI.pm's sticky checkboxes and to use HTML::Template for templates. (I don't want to use CGI.pm to create and display the entire form using the 1995-ish technique of $q->start_html; $q->start_form [etc.]; $q->end_form; $q->end_html; in the script, even if that seems to have been a good and novel idea back in the day.)
So my script creates a sticky checkbox by calling $q->checkbox( -name => "member" ). CGI.pm returns a string of HTML that can be sent over to the template, where there is a <TMPL_VAR MEMBER_CHECKBOX> embedded in its text, waiting to receive the HTML for the checkbox, which might be checked due to CGI.pm's stickiness, or might not be.
Alas, the sticky feature still wasn't working. A "view source" revealed that the magic <input type="hidden" name=".cgiparams" value="member"> wasn't part of the form in the generated web page. But, of course, why should it be? I hadn't sent it over to the template. But where is CGI.pm generating that string? How do I get it?
It turns out that the string containing the hidden list of fields is prepended to </form> when CGI.pm's $q->end_form() is called. But beware (ask me how I know), this is the case only if $q->start_form() has been called before $q->checkbox() was called. it's not enough that the CGI module was instantiated. My template had its own <form action="https://yaddayadda.com/script.cgi"> and its own </form> tag, so I hadn't thought of using needing to call CGI->start_form() or CGI->end_form(). I only needed the creation of the sticky checkboxes.
What wasn't intuitive to me, and might be useful to others, is that I needed to have my script actually call something like my $throwaway_string = $q->start_form(); somewhere before $template->param( MEMBER_CHECKBOX => $q->checkbox(-name => "member") ); and then needed to send over the list of hidden fields by doing something like my $hidden_list_of_fields_and_closing_form_tag = $q->end_form(); -- after the last checkbox or any other form field had been created by using a CGI.pm function -- followed by something like $template->param( HIDDEN_LIST_OF_FIELDS_AND_CLOSING_FORM_TAG => $hidden_list_of_fields_and_closing_form_tag );
I don't need to send over the results of start_form(); I just need to have called it. The sticky checkboxes work even with the <form action=...> that's hard-coded in my template. But apparently I do need to call start_form() in order for CGI.pm to start paying attention and keeping a list of the names of the checkboxes (or other HTML form elements) that it's thereafter creating, so that $q->end_form() knows what to return in the way of a hidden list of fields.
I know that a web application platform might handle this particular edge case behind the scenes, but I'm not sure. I've done some development with Dancer2, but even that fine platform seems to assume that the developer has picked and implemented some Perl module (ideally, one that's more recent and more sophisticated than CGI.pm) to handle the creation of form elements, and to somehow handle this checkbox edge case.
Edited for clarity, probably unsuccessfully due to author's inability to communicate precisely :-)
Here is my understanding of what the theory behind what I am trying to do is, correct me where I am wrong, also please check my questions at the end:
The intersection of N hyperplanes (Ndim) is also known as the solution to "the system of N linear equations(=planes) with N variables". However, I am interested in the case when I have less equations. The result is not a single point in Ndim but a lower-dimensions plane. For example in 3D. The intersection of 3 planes (M=3, N=3), assuming any pair is not parallel, is a single 3D point and the intersection of 2 planes (M=2, N=3) is a line. In Ndim, the solution would be an Mdim hyperplane "living" in Ndim. Below, I call this a "hyperline".
An example of the above problem is in this SO question. The result is the equation of the intersection line in parametric form. Arbitrary values of the parameter t yields a point on this line. Ideally this is what I want to achieve: finding points on the intersection of the planes.
Solving the system of N linear equations with N variables (Ndim) can be done with, for example, Math::Matrix. Given N planes in the form a1x+b1y+c1z+...n1=0 etc., a matrix A is formed with each row being [a1, b1, c1, ..., n1] etc. then:
Math::Matrix->new([[a1,b1,c1,...,n1],...])->solve->print;
I have experimented with solve() for the case of M linear equations (Ndim) where M = N-1:
and the missing 3rd dim is the parameter t itself: z = t. And I can get a point on that line by setting t to an arbitrary value. I can verify that this point is on each plane by substituting the point's coordinates into each plane equation.
I have also experimented with transforming the planes matrix to the Reduced Row Echelon Form. Which makes it convenient to work out the "hyperline" equation. This functionality is offered by Math::MatrixLUP :
Two planes are parallel when their normal vectors (the coefficients of the dimensions: a, b, c, ... (but not the constant n) are multiples. E.g. nv1 = k * nv2. And this translates to checking if all the ratios of the coefficients : a1/a2 = b1/b2 = c1/c2 = ... are the same. My question is: what happens if any coefficient is zero (or actually both coefficients (e.g. a1 and a2) are zero?
How can I calculate the intersection when M < (N-1)? I.e. above I am always checking the intersection of M planes in Ndim where M = N-1. But what if there are even less planes? e.g.
my @planes5D = (
[1, 2, 1, -2, 3, -1], # ax+by+cz+n=0
[2, 3, -2, 4, -4, 2],
[3, -1, -2, -5, 6, 2],
# only 3 planes (it was successful with 4)
)
In short, does the parametric equation of the intersecting "hyperline" contain 2 parameters now?
When I test test_in_beast_space which produces random planes in 666 dimensions, it fails to detect that a point on the intersection "hyperline" lies on all the planes. To do that I substitute the point in each plane equation and expect to have result as zero. However, it's not an exact zero. That's why I am doing a range test to check if it's close to zero. Well the closeness $SMALLNUMBER for 5 dimensions can be as small as 1E-09. But for these many dimensions it can be as low as 1E-02. Is the accuracy lost in summing 666 multiplications that much really?
I guess Math::Matrix::solve() is safe to be used for MxN matrices (e.g. M equations=planes in N unknowns (dimensions) where M<N)? From solve() of Math::Matrix :
Solves a equation system given by the matrix. The number of colums mus
+t be greater than the number of rows. If variables are dependent from
+ each other, the second and all further of the dependent coefficients
+ are 0. This means the method can handle such systems. The method ret
+urns a matrix containing the solutions in its columns or undef in cas
+e of error.
The edge cases where the 1st dimension is zero for all planes in 5D and when the 1st+2nd are zero, fail. How can I find the intersection in this case?
Edits: updated the demo to correct the sub are_planes_parallel() as per the comments of hippo and LanX about what happens when plane-equation coefficients are zero.
In 1998, a friend gave me a computer. It was in pieces. I knew nothing about nothing. Within a year, I was communicating over dual telephone lines. Within two years of that, I was a sysadmin at an ISP. This was the year I found Perlmonks. I read a book, 'Perl in 21 days' or some such, and found Perl was what I wanted... a way to automate processes.
Within months, I learned a dangerous amount about MySQL, CGI and Perl to allow any invader to break everything. Thankfully, during that time, everyone was out for themselves, and exploitation hadn't yet become a thing.
By 2009, I'd grown a lot in many areas. No where near perfect in the security arena, but I was becoming proficient on how to interact with the open source world, and how to interact with the CPAN. It was this year that I joined Perlmonks as a member, and became a vocal person, not just a listener.
Now, as some of the old timers will attest to, I always claimed "I'm not a programmer". With that said, I have done much work in fields so closely related to programming, that I have to bend and say that yeah, maybe I can classify as a hacker.
Anyone else around who have claimed "I'm not a programmer", or who has been around since the very early days of Perlmonks who would just like to say "I'm still here!!!"?.
Houston PM's private, self hosted email list (using Sendy/AWS SES - PHP sorry xD) - monthly meeting announcements will be from noreply@houstonperlmongers.org and reply-to is to brett.estrade@gmail.com. I'm working getting the link/form up on the Houston Perl Mongers site, https://houstonperlmongers.org (or houston.pm.org). Keeping up with all the outlets is too much, so going back to email and website announcements. I may still post here; July's meeting has not yet been set.
I needed to generate random strings from a regular expression and I have found (*) a C++ library (regxstring C++ library by daidodo) which does just that and works fine for my use case. It claims that it supports most Perl 5 regexp syntax. It is quite fast too. So I have ported it into a Perl module, here : String::Random::Regexp::regxstring.
The XS and C++ code bridging Perl to C++ library are very simple and can serve as an example for doing that for other libraries. Go forth and multiply.
