perlfaq6:

In versions 5.6 and later, Perl won't recompile the regular expression if the variable hasn't changed, so you probably don't need the /o option. It doesn't hurt, but it doesn't help either.

perlop:

... the largely obsolete /o ...

The bottom line is that using /o is almost never a good idea.

Then what about something like benchmark below (this is 5.42, and I _do_ see a small but noticeable performance bump with real code which does some heavy lifting when parsing. I don't think any variables have changed; just wanted to split pieces of a regex into separate variables for clarity):

use strict;
use warnings;
use feature 'say';
use Benchmark 'cmpthese';

my $pat = qr/\d+/;
my $s = '123abc' x 1e6;

cmpthese -1, {
    foo => sub { 1 while $s =~ /\G $pat \D+ /cgx },
    bar => sub { 1 while $s =~ /\G $pat \D+ /cgxo },
};

__END__

          Rate  foo  bar
foo  1213522/s   -- -88%
bar 10345112/s 752%   --
[download]

So I am looking around in perlvar and I learn that if you preface a scalar variable name with an underscore it will by default be in the main package...wow, I think. I want to try that:

perl -e 'package Nether; our $val = 2000; my $_nonesuch = 3000;  packa
+ge main; print __PACKAGE__ . qq~\t~ . $main::_nonesuch;'
[download]

Makes: main

What? ...what happened by my value? So I take away the package portion:

perl -e 'package Nether; our $val = 2000; my $_nonesuch = 3000;  packa
+ge main; print __PACKAGE__ . qq~\t~ . $_nonesuch;'
[download]

main 3000

As an aside I should mention why I keep posting these cryptic things about basic Perl functionality. I am researching why people run into problems with Perl and give up. The target audience (for now) includes project management and product owners who have enough familiarity with the language to recommend its use but want to simultaneously reduce the backlash that might come from doing so.

Acme::MetaSyntactic (script/ is typical)
EXE_FILES: script/meta script/metafy

Pod::Parser
EXE_FILES: scripts/podselect

CGI-Kwiki
EXE_FILES: inc/SCRIPTS/kwiki-install

GD
EXE_FILES: bdf_scripts/bdf2gdfont.pl

App::FatPacker (bin/ is typical too)
EXE_FILES: bin/fatpack

Despite all that, everything listed as EXE_FILES ends up in the same directory, specified (on my system) by 12 %Config variables with the same exact value as $Config{bin}:

/Users/u/perl5/perlbrew/perls/perl-5.42.0/bin

My question is this: do these 12 Config variables have the same value on all Perl installations? I guess there are actually 14 of these same vars, but the vendor values are blank on my system.

Here's a little script to check. I'd like to know if these can be different values so I know which one(s) to use. Thanks in advance.

#!/usr/bin/perl -l
# Check if all the bin and script dirs in %Config are the same.

use strict;
use warnings;
use Config;

@_ = qw/bin
binexp
initialinstalllocation
installbin
installscript
installsitebin
installsitescript
scriptdir
scriptdirexp
sitebin
sitebinexp
sitescript
sitescriptexp
vendorbin    
vendorbinexp/;

printf "%-24s  %-100s\n", $_, $Config{$_} for @_;
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bin                       /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
binexp                    /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
initialinstalllocation    /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
installbin                /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
installscript             /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
installsitebin            /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
installsitescript         /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
scriptdir                 /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
scriptdirexp              /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
sitebin                   /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
sitebinexp                /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
sitescript                /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
sitescriptexp             /Users/u/perl5/perlbrew/perls/perl-5.42.0/bin                                                    
vendorbin                                                                                                                     
vendorbinexp                                            

% corelist List::Util
List::Util was first released with perl v5.7.3

https://metacpan.org/dist/Scalar-List-Utils/changes:

1.44 -- 2016/03/17 23:08:46
        CHANGES
         * Added List::Util::uniq() and uniqnum()

% corelist -a List::Util | grep 1.44
NOPE

% corelist -r | grep 2016
v5.22.2     2016-04-29
...

% perldoc -lf splice                                                                             
/Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/5.42.0/pods/perlfunc.pod
/Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/5.42.0/pods/perlop.pod

% grep 'splice' /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/5.42.0/pods/perlfunc.pod
L<C<splice>|/splice ARRAY,OFFSET,LENGTH,LIST> has three scalar arguments
... (19 lines deleted for brevity)

% grep 'splice' /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/5.42.0/pods/perlop.pod
% <- NOTHING!

shell> perldoc perlootut
[download]

"...This document was created in February, 2011, and the last major revision was in February, 2013....

I check metacpan...same document. I want to learn the latest techniques for OO in Perl. I remember reading that there were native classes added in 5.38. Is someone updating perlootut? Is is being superseded by another POD?

Sample string: "AB ABDA DCACCB AAA BSAA CAAB ACS ABA DBA BA DASSABACA A"

I'm looking for either: BA[ABC]{2} OR CA[CD]{2} OR DA[SC]{2}

So, I would write: /BA[ABC]{2}|CA[CD]{2}|DA[SC]{2}/

Is there a way to get a return value of 1, 2, or 3 depending on which pattern was matched first? How would I do that?

By now, I am sure you have heard of the "732 bytes of Python code to root every major Linux distro."

(I checked it out -- it works. Don't run it on your own machine, though, as it will mangle your `su` binary).

At any rate -- I figured, we can make it smaller in Perl!

A half hour and a bunch of tokens later, I failed. My smallest version is 767 bytes. Can anyone here do better?

Hi Monks. I don't know if anyone can help me with this, but I'll ask anyhow.

I'm doing this on the commandline:

$ PERL5LIB=~/build/perl-testing-libs/lib/perl5 cpanm --self-contained \
--exclude-vendor -L ~/build/perl-testing-libs --wget --skip-satisfied \
--interactive --verbose YAML::LibYAML

The resulting message is

! Installing the dependencies failed: Module 'Test::More' is not installed
! Bailing out the installation for File-Temp-0.2312.
! Installing the dependencies failed: Module 'File::Temp' is not installed

When I try to build the two required modules alone, I can't get a succcessful installation. What's going on?

EDIT

Sorry,I was tired and in a hurry and didn't give much contextual info. My System and my Perl are:
OS: CYGWIN_NT-10.0-26200; cpu type: x86_64; |12| cores, cpus present: |1|
Perl version v5.40.3, CygPerl.

    – Soren

So I write a response to this blogs.perl.org post titled, 'Who Tests the Tester? Me!!!' by lichtkind and almost as soon as I hit the submit button I take a closer look at my test and say, 'oops...I forgot to change the class to the new subclass...I'll just change that and rerun my tests. No problem...'

t/01.t ............ ok
t/hsltupletest.t .. 1/? 
#   Failed test 'A is now between 0 and 360 since it is degrees'
#   at t/hsltupletest.t line 22.
# Looks like you failed 1 test of 6.
t/hsltupletest.t .. Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/6 subtests 
t/tupletest.t ..... ok

Test Summary Report
-------------------
t/hsltupletest.t (Wstat: 256 (exited 1) Tests: 6 Failed: 1)
  Failed test:  6
  Non-zero exit status: 1
Files=3, Tests=12,  0 wallclock secs ( 0.08 usr  0.02 sys +  0.49 cusr
+  0.07 csys =  0.66 CPU)
Result: FAIL
[download]

Denied!

Debugging reveals something extremely strange...

main::(./t/hsltupletest.t:8):    my $prospectTupleRef = [qw~a b c~];
  DB<1> n
main::(./t/hsltupletest.t:10):    my $tuple = HSLTuple->new($prospectT
+upleRef, 'HSL');
  DB<1> n
main::(./t/hsltupletest.t:12):    ok($tuple->is_valid($prospectTupleRe
+f) == 0, "A B C is an array but not an HSL tuple");
  DB<1> x $tuple
0  FakeTuple=HASH(0x5b2e6ee12a70)
   'axes' => 3
   'space_name' => 'HSL'
   'tupledata' => undef
  DB<2>
[download]

What? It says it is a FakeTuple even though I clearly used the HSLTuple! Unsurprisingly, it calls the is_valid() method of FakeTuple:

main::(./t/hsltupletest.t:20):    ok($tuple->is_valid([qw~361 62 99~])
+ == 0 , "A must be between 0 and 360 since it is degrees");
  DB<2> s
FakeTuple::is_valid(FakeTuple.pm:34):
34:        my ($self, $data2Check) = @_;
  DB<2> l
34==>        my ($self, $data2Check) = @_;
35:        my $result = 0;
36:        for(0..2){$result++ if ($data2Check->[$_]=~m/\d+/ && 
37                         $data2Check->[$_] >= 0    &&
38                     $data2Check->[$_] <= 100)};
39         
40:        return ( $result == $self->no_of_axes() ) ? 1 : 0;
41     }
42     
43     # code (loosely) borrowed from Basis.pm
  DB<2>
[download]

Why did it not use my derived class and call my overridden method?