I am learning Perl using a book downloaded from the internet.

Opal is a system for charging fares on public transport in NSW Australia. I have had four Opal cards and they identified by 16 digit numbers. I have four target directories into which the files related to these cards go and I have tried to set up a hash to map between card numbers and the destination directories but it does not work and the error messages make no sense to me.

This is the current form of the hash definition which is at line 26 in the script:-

my %OCN_PFX_To_TDir=( 
   3085220111379778 => '3085220111379788_Rexx',
   3085220334620644 => '3085220334620644_Spare',
   3085220346432582 => '3085220346432582_Rexx2',
   3085220352420034 => '3085220352420034_Algol'
    );
This is the input followed by the error messages I get:-

carl@md-tower-004:~$ perl ~/bin/copy_opal1.plx 
Can't modify constant item in scalar assignment at /home/carl/bin/copy
+_opal1.plx line 26, near ");"
Execution of /home/carl/bin/copy_opal1.plx aborted due to compilation 
+errors (#1)
    (F) You aren't allowed to assign to the item indicated, or otherwi
+se try
    to change it, such as with an auto-increment.
Uncaught exception from user code:
    Can't modify constant item in scalar assignment at /home/carl/bin/
+copy_opal1.plx line 26, near ");"
    Execution of /home/carl/bin/copy_opal1.plx aborted due to compilat
+ion errors.
[download]

I am writing a small program to copy Opal related files from my downloads directory to the appropriate destination directories.

Basically it tells me that I am trying to assign a scalar value to the % sign representing the modulus operator which cannot receive such a value but the % sign is to mark the variable as being a hash. I have tried various changes on the definition, originally I had both keys and values in double quotes now I have the values in single quotes, originally I used commas to separate key value pairs. No matter what I change the error messages remain the same.

It may be that the book I downloaded is old and some syntax suggested in the book no longer works but no matter how many queries I have put into Google and how many AI overviews I have seen and hit list links that I have followed nothing has confirmed this.

Hello Monks and Nuns. I was working with cpan (the installer) on CygPerl today and tried the command recent; it didn't work and this is what I saw:

cpan2> recent
CPAN: XML::LibXML loaded ok (v2.0210)
Fetching 'http://search.cpan.org/uploads.rdf'
CPAN: LWP loaded ok (v6.80)
DONE

Catching error: "XML::LibXML::Error=HASH(0xa01ebe148)" at /usr/local/share/perl5/site_perl/5.40/CPAN.pm line 397.
        CPAN::shell() called at -e line 1

Could anyone else try this and see what happens? I'd appreciate it.

My system setup is:

This is perl 5, version 40, subversion 3 (v5.40.3) built for x86_64-cygwin-threads-multi
/usr/lib/perl5/vendor_perl/5.40/x86_64-cygwin-threads/XML/LibXML.pm
XML::LibXML version 2.0210
CPAN        version 2.38
@INC:
/usr/local/lib/perl5/site_perl/5.40/x86_64-cygwin-threads
/usr/local/share/perl5/site_perl/5.40
/usr/lib/perl5/vendor_perl/5.40/x86_64-cygwin-threads
/usr/share/perl5/vendor_perl/5.40
/usr/lib/perl5/5.40/x86_64-cygwin-threads
/usr/share/perl5/5.40

Greetings, wise monks,

I am trying to crank down restrictions on an FCGI script. I have DBI opening an SQLite3 database as read-only. This is how I am currently connecting to the database:

    my $dbh = DBI->connect("dbi:SQLite:dbname=$database", 
                undef, 
                undef, 
                { 
                  AutoCommit => 0,
                  RaiseError => 1,
                  on_connect_do => "PRAGMA foreign_keys = ON",
                  sqlite_open_flags => "DBD::SQLite::OPEN_READONLY",
                })
        or die("Could not open database '$database': $!\n");
[download]

However, AppArmor still gives the following error about needing write access, even though the error and restrictions causing it do not impair the script from appearing to work as expected:

2025-11-04T14:02:51.130580+00:00 ID28399 kernel: [5084204.347595] audi
+t: type=1400 audit(1762264971.124:63): apparmor="DENIED" operation="o
+pen" profile="/var/www/fcgi/foo.fcgi" name="/var/www/db/foo.sqlite3" 
+pid=377569 comm="search.fcgi" requested_mask="wc" denied_mask="wc" fs
+uid=1002 ouid=1002
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and in the AppArmor profile:

        /var/www/db/foo.sqlite3 kr,
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If I add w to that, the errors go away. However, I don't want to do that because the script's access is supposed to remain read-only. Yet it appears that DBI is somehow still requesting some kind of write access, even if it does not use it. What can I change in the DBI connection to ensure that it is purely read-only as far as the database goes?

use strict;
use Devel::Peek;
$Devel::Peek::pv_limit = 3;
use warnings;
printf "$^V\n";
my $s = 's' x 32;
Dump $s;
my $addr = pack 'p', $s;
printf "Q: hex: %x, dec: %1\$d\n", unpack 'Q', $addr;
Dump $s;

__END__

v5.32.1
SV = PV(0x1fbf48) at 0x24f0e08
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x2565cb8 "sss"...\0
  CUR = 32
  LEN = 34
Q: hex: 2565cb8, dec: 39214264
SV = PV(0x1fbf48) at 0x24f0e08
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x2565cb8 "sss"...\0
  CUR = 32
  LEN = 34

v5.42.0
SV = PV(0x1330f20f4c0) at 0x1330f2836a0
  REFCNT = 1
  FLAGS = (POK,IsCOW,pPOK)
  PV = 0x1330f3129f0 "sss"...\0
  CUR = 32
  LEN = 40
  COW_REFCNT = 1
Q: hex: 1330f312400, dec: 1318809838592
SV = PV(0x1330f20f4c0) at 0x1330f2836a0
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x1330f312400 "sss"...\0
  CUR = 32
  LEN = 34
[download]

Previously (5.32), there was consistency as expected: PV address was "real" RAM address; and simple fact of "packing to pointer" didn't change scalar' guts. Now, I see some weird huge ("virtual"?) addresses -- even though everything works (including, not shown above, accessing (or acquiring, same values) these pointers from C). Where such numbers come from, is this the new normal? Is difference in "Dump" output related to that, or totally another issue?

I'm an inexperienced Perl programmer (my background is mainly in Python), charged with keeping a legacy app running, and I'm having trouble figuring out how to validate a date. (At least, that's what I think the problem is.)

We have a function that takes a date value and does some transformations on it. This is thoroughly tested and works fine for its use case, but we don't actually have a test for what happens if someone sends garbage into it—it assumes the input really is a valid date. Normally, this is fine; the input comes from internal sources and should always be OK. We now need to extend it for a case when we don't have control over the incoming data. So, I tried to wrap it in an eval to catch any errors. Currently, it looks like this:

# in MyApp::Util
sub convert_datetime {
    my ( $self, $incoming_datetime ) = @_;

    my $new_dt;
    eval { $new_dt = DateTime::Format::ISO8601->parse_datetime( $incom
+ing_datetime ); };
    return undef if $@;
    # No error, now we can convert the date (not shown)
}
[download]

my $bogus_datetime = MyApp::Util->convert_datetime("FOO");
is ($bogus_datetime, undef, "convert_datetime doesn't blow up if sent 
+bogus date");
[download]

ok 141 - convert_datetime doesn't blow up if sent bogus date
Invalid date format:  at /path/to/MyApp/Util.pm line 818.
    eval {...} called at /path/to/MyApp/Util.pm line 818
    MyApp::Util::convert_datetime("MyApp::Util", "FOO") called at t/Ut
+il.t line 297
    ...propagated at t/Util.t line 298.
[download]

So the test "works" in that it returns an "ok" value, but it also prints the whole "Invalid date format" thing. How do I get it to _not_ do this, or otherwise test to see if the input is valid before I pass it to DateTime::Format::ISO8601->parse_datetime? The docs for this function say "The parse_datetime method will attempt to match these ambiguous strings" etc., but doesn't say what happens if it can't, or what you're supposed to do to test for valid input.

I tried to write a test script, but even though it looks identical (to me), this does _not_ print the "Invalid date format":

#!/usr/bin/env perl

use strict;
use warnings;

use DateTime::Format::ISO8601;
eval {my $foo = DateTime::Format::ISO8601->parse_datetime("FOO");};
print "ERROR\n" if $@;
[download]

Running this simply prints "ERROR" and that's it, no other output. What's going on in the real code, or what's the right way to handle this?

Wise Monks,

I am doing an in-place replacement in a text file which succeeds but one (?) extra newline is added at the end of the file:

The input file (a):

1
2
3
[download]

The command:

Output

1
4
3

# there is an extra newline at the end, above
[download]

Looping the above command (the replacement is done only the first time), will yield as many newlines at the end:

for i in $(seq 1 10); do perl -i.x -lp0e 's/2/4/gs' a; done
[download]

bw, bliako

Dear Monks,

I can not understand why this works:

my $x = <<'EOX';
A {
  B 123
  C xyz
}
EOX
$x =~ s/A\s*\{.+?\}//s;
print "x='$x'\n"; # empty
[download]

but this does not (linux terminal):

perl -pe 's/A\s*\{.+?\}//s' <<'EOX'
A {
  B 123
  C xyz
}
EOX
# prints exactly what the input is
[download]

I have checked if there are mistaken shell interpolations to the oneliner script, but there are not, I think:

x='s/A\s*\{.+?\}//s'
echo $x
# s/A\s*\{.+?\}//s
[download]

Edit: the same problem if the oneliner operates on a file:

cat > infile<<'EOX'
A {
  B 123
  C xyz
}
EOX
perl -pe 's/A\s*\{.+?\}//s' infile
# or perl -i -pe 's/A\s*\{.+?\}//s' infile
[download]

Is there any IPv6-capable "paranoid" DNS resolver like Net::DNS::Paranoid, except with support for IPv6?

I'm currently writing a "link preview" fetcher, using Mojo::UserAgent. As this preview fetcher mildly implies fetching user-generated and/or user-controlled links (even though the application is primarily for myself), I'm looking for something like LWPx::ParanoidAgent / LWP::UserAgent::Paranoid / HTTP::Tiny::Paranoid, but for Mojolicious.

I have already resolved (hah!) myself to writing Mojo::UserAgent::Paranoid, which delegates (as they all do) the DNS resolution to Net::DNS::Paranoid, a DNS resolver class that blocks hosts and IP addresses that are unlikely URLs for external services, especially localhost and other internal networks (192.168.*, 10.* and the multicast addresses).

This is all fine and good, if it weren't for IPv6. Net::DNS::Paranoid happily lets ::1 through, as the code mostly looks at IPv4 addresses and its DNS resolution also only speaks A records, not AAAA.

Simply adding ::1 (localhost in IPv6-speak) to the list of blocked hosts is a good start, but I would also want to block the multicast and link-local IPv6 addresses and some others. So, I'm mildly looking towards extending Net::DNS::Paranoid to also support IPv6, but maybe somebody has already done the work, or has links to an existing implementation in another language where I can crib the pitfalls and footguns from.

OS=Linux

I'm struggling to send special characters like umlauts ("äöüÄÖÜ") via X11::GUITest and SendKeys() to another application.

Is there a trick I am missing? Anything after the first special character is discarded.

If I try the linux tool xte from the package 'xautomation', it works fine from the console:

gnome-text-editor & sleep 1; xte "str äöüÄÖÜß"