I wrote a fragment of code dealing with passing pointers to pointers to data for some FFI calls. Reducing it now to SSCC(?)E: if written as

pack 'P', pack 'P', $data
[download]

then Perl warns "Attempt to pack pointer to temporary value", so it's easy to debug. But in my case, it was something like:

sub foo { pack 'P', $_[0] } foo pack 'P', $data;
[download]

-- no warnings, correct result for single call, but incorrect if return values are not used immediately but e.g. stored. Then I ran some tests:

>perl -MDevel::Peek -we "Dump 1; sub foo{Dump $_[0];$_[0]=1} foo(1)"
SV = IV(0x653478) at 0x653488
  REFCNT = 1
  FLAGS = (IOK,READONLY,PROTECT,pIOK)
  IV = 1
SV = IV(0x653358) at 0x653368
  REFCNT = 1
  FLAGS = (IOK,READONLY,PROTECT,pIOK)
  IV = 1
Modification of a read-only value attempted at -e line 1.

>perl -MDevel::Peek -we "Dump 1+1; sub foo{Dump $_[0];$_[0]=1} foo(1+1
+)"
SV = IV(0x2612cf8) at 0x2612d08
  REFCNT = 1
  FLAGS = (PADTMP,IOK,READONLY,PROTECT,pIOK)
  IV = 2
SV = IV(0xfcb140) at 0xfcb150
  REFCNT = 1
  FLAGS = (IOK,pIOK)
  IV = 2
[download]

Why is not PADTMP flag copied to $_[0], and why, if present, it also prevents copying READONLY?

PATTERN1 SOME INFO

TEXT1

TEXT2

TEXT3 PATTERN2 SOME INFO

PATTERN1 SOME INFO

TEXT4

TEXT5

TEXT6 PATTERN3 SOME INFO
[download]

I know the following code perl -ne 'print if (/PATTERN1/../PATTERN3/)' is a greedy match and prints everthing.

What I want is to print the following output

PATTERN1 SOME INFO 

TEXT4 

TEXT5 

TEXT6 

PATTERN3 SOME INFO
[download]

Note this is extremely large file and can't put the whole file into a string.

Thanks, Ravi

I often have the case when reading a binary value from a file that it also has a textual representation. So I can use the dualvar functionality of Scalar::Util to solve this issue.

But that's not enough for me. Usually I have a corresponding table which contains the valid values and its representations. To avoid doing the same checks so often in code, I decided to tie the read scalar variable to a package which is doing these checks for me. Additionally on a change it shall always update the numeric and string context.

Here an example:

#!/usr/bin/perl

use strict;
use warnings;

use My::DualVar;

my %table = ( 1 => 'NORTH',
              2 => 'SOUTH',
              3 => 'EAST',
              4 => 'WEST' );

# Case 1: Table num -> str
print "Case 1: Dualvar via num2str table\n\n";
{    
    my $direction = 2;
    My::DualVar->tie($direction, \%table);
    print_dualvar($direction);

    $direction = 4;
    print_dualvar($direction);

    $direction = 'NORTH';
    print_dualvar($direction);
}

# Case 2: Table str -> num
print "Case 2: Dualvar via str2num table\n\n";
{    
    my $direction = 'SOUTH';
    My::DualVar->tie($direction, reverse %table);
    print_dualvar($direction);

    $direction = 4;
    print_dualvar($direction);

    $direction = 'NORTH';
    print_dualvar($direction);
}

sub print_dualvar
{
    print "as num: " . ($_[0]+0) . "\n";
    print "as str: $_[0]\n";
    print "\n";
}
[download]

And here my written package:

This code is working. But I would be interested in your opinion. What could I do better?

And the second thing. Currently my code would work randomly if the values of the given table (hash) are not unique. Is there an efficient way to check whether the values of a hash are unique? Then I would reject such a hash

Or would there be a solution to return several values if the hash is not unique, e.g. key 2 and 5 would have value 'SOUTH'?

In numeric context it would not work. If I would set a dualvar variable to 'SOUTH', then I would have to return 2 or 5 in the FETCH-method. Perhaps in numeric context the smaller value should be returned.

In string context I think it is possible. Because I could give back a concatenated string and I still would have a scalar.

I have two files, I have to update file 1, with the values from file2. for ex: in file1, ON_DIE_FILLER/filler_fuse should get value 0xa

I am having issues in comparing the names.

file 1:
ibl_ss_fuse_c0_r0/MRA_PVT_Tuning = 0x94, 
ibl_ss_fuse_c0_r0/S3M_SPARE_1B7_3to7 = 0x0, 
ON_DIE_FILLER/filler_fuse = 0x0, 
ON_DIE_FILLER/filler_byte = 0x0, 




file 2:
die0_IAX_fuse_dino_c1_r0, die0_IAX_fuse_dino_c1_r0_IAX_fuse_iax_wr_ass
+ist_pulsewidth, 0x5,
die0_ON_DIE_FILLER, die0_ON_DIE_FILLER_ON_DIE_FILLER_filler_byte, 0xb,
+ 
die0_ON_DIE_FILLER, die0_ON_DIE_FILLER_ON_DIE_FILLER_filler_fuse, 0xa
[download]

As the title says: on Linux, if you assign anything to $0 (with the intent to change the program's name as displayed by ps et al.), not just the the program's name and arguments are changed, but the environment (as shown in /proc/PID/environ) is cleared as well, or more precisely, filled with spaces.

The perlvar entry for $0 contains a paragraph that vaguely alludes to this:

            In some platforms there may be arbitrary amount of padding, for
            example space characters, after the modified name as shown by
            "ps". In some platforms this padding may extend all the way to
            the original length of the argument area, no matter what you do
            (this is the case for example with Linux 2.2).

So I kind of understand what happens here and why, I just find it rude.

It is somewhat more concerning that the effect persists even if you localize $0.

#!/usr/bin/perl

sleep 10;
{
    local $0 = 'changed';
    sleep 10;
}
sleep 10;
[download]

When you run the program above, and watch a process list in a different terminal, you can observe that the apparent process name changes to 'changed' after 10 seconds, then changed back again, but if you watch the contents of /proc/PID/environ at the same time, you can see that it gets filled with spaces, then doesn't change back.

Two additional things to note:

• The fake process name (as assigned to $0) spills over the memory that formerly contained the environment, so if you do something like $0 = 'changed' x 10000, /proc/PID/environ will contain something like "angedchangedchanged...changed\x00 ...".
• When the localized $0 goes out of scope, Perl only makes a weak attempt to change the process name back to its original. So if you originally ran the program with arguments, the output of ps contained something like "perl foo.pl -a -b -c", but after restoration it will just be "foo.pl".

I think that an argument could be made that Perl should try to preserve the contents of /proc/PID/environ when changing $0, and do a more thorough job of restoring the original command line if $0 is localized.

Hi, I am trying to run a perl command through linux console using filehandle ($_ sign) in order to indicate a file to use when running the command. The commands from the code snippet below are from https://metacpan.org/pod/ntheory

>perl -Mntheory=:all -nE "chomp; say is_prime($_);" input.txt
1
>perl -Mntheory=:all -nE "chomp; say length($_);" input.txt
33
[download]

>perl -Mntheory=:all -nE "chomp; say is_prime($_);" input.txt
Parameter 'inputtxt' must be a positive integer at -e line 1, <> line 
+1.
>perl -Mntheory=:all -nE "chomp; say length($_);" input.txt
Parameter 'inputtxt' must be a positive integer at -e line 1, <> line 
+1.
[download]

I got some great advice for putting together my websocket client here: Mixing asynchronous data feed with synchronous program flow control. And it’s working well.

10,000 foot view: I am consuming a stock price stream. This is a paid service that only allows one connection and it is somewhat fragile due to a short timeout period, a dearth of documentation, and no built-in caching/reconnecting. None of my plans breach the user agreement/contract; that’s not me.

I don’t want to write a cache/queue. I want to leave the stream alone and uncluttered with a bunch of synchronous calls that might throw exceptions or otherwise cause trouble; separation of concerns. I also want to test multiple versions of code against the single stream concurrently. I could record and play back data but that’s a pain, a disk hog, and it doesn’t address the fragility/complexity or any possible application of code against live data.

My ideas have been–

• proxy the websocket through nginx so multiple “muted” client connections still only share the single permissible connection to the real service (I’m not sure this is possible without a lot of code and it’s extra plumbing),
• write a websocket server, in Mojo still, around the websocket client that lets an arbitrary number of local clients receive an echo of the master client’s stream,
• write a simple streaming socket server in Perl that runs the websocket client and pushes out to any local socket clients,
• publish the data stream to a local DB (this would be slower than everything else if it’s relational but also perhaps the most reliable with a built-in “cache/queue” only in need of pruning),
• or come beg you guys for what is probably a better idea than I can summon.

So… I guess the last one. :P

Hello monks. I was using perl to translate files from one format to another with something like the following: perl -p translation.pl file.in > file.out when I got lazy and decided that I should be able to just pass a list of input files, and let perl append .out (or replace the extension) to create an output file for each input file.

There are obviously more than one way to do it and I settled for:

for my $filename (@ARGV)
{
  open my $input, '<', $filename or die "Couldn't open $filename: $!";
  open my $output, '>', $filename.'.new' or die "Couldn't open $filena
+me: $!";
  while (<$input>)
  {
    say $output translate($_);
  }
}
[download]

Now I'm wondering, is there some simpler way to do it? This looks like a pretty common task, and it is very close to what -i does, except the two files are swapped: I want the output in the file with the added extension and the original unchanged. There doesn't seem to be an option for it, so do you know of some hack (bring out your secret operators, I'm asking out of curiosity so I want even the bad answers :D ) or some module that would let me write my code without having to write the explicit while(<>) loop on the data?

NB: yup I already just asked that in the CB and got some answers. Like choroba's proposition to call the translation.pl file inside a shell loop to handle the output files.

Edit: perl -pE "open STDOUT, '>>', qq<$ARGV.txt>; s/(.*)/\U$1/;" FILES works once :P (inspired by choroba's proposition)