Re^2: pack() returns an unusable string

I would guess that your packed string '$p' has either a single quote "'" in it or an escape or $ or @ at the end that eats the closing single quote

I should add that there's nothing special about the given NV value of 2.4.
The behaviour I'm seeing is happening for all NV values that I've tested.

To get a dump of $s:

# test.pl

use warnings;
use Devel::Peek;

$template = 'D<';
$nv = 2.4;
$p = pack $template, $nv;
$s = "'$p'";

Dump $s;

system $^X, '-wle', "print unpack('H*', $s);";
[download]

That outputs the following (which does, at least, contain an "@"):

C:\_32\pscrpt>perl test.pl
SV = PV(0x4bcf98) at 0x571248
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x4b7e88 "'\232\231\231\231\231\231\231\231\0@\0\0\0\0\0\0'"\0
  CUR = 18
  LEN = 20
Can't find string terminator "'" anywhere before EOF at -e line 1.
[download]

But if I change the value of $nv to 2.4e100, I get:

C:\_32\pscrpt>perl test.pl
SV = PV(0x3ecf98) at 0x383348
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x3e7e88 "'\vL\177v\257zb\206\264>\0\0\0\0\0\0'"\0
  CUR = 18
  LEN = 20
Can't find string terminator "'" anywhere before EOF at -e line 1.
[download]

Interestingly, changing the value to 3.1e-100 results in a different warning:

C:\_32\pscrpt>perl test.pl
SV = PV(0x26cf98) at 0x5311f8
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x267e88 "'9\302\271\243\"\211\224\255\264>\0\0\0\0\0\0'"\0
  CUR = 18
  LEN = 20
Use of uninitialized value $_ in print at -e line 1.
[download]

Perhaps something to do with the internal double quote.

For a value of 13.16e-100, I get:

C:\_32\pscrpt>perl test.pl
SV = PV(0x38cf98) at 0x4c51b8
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x387e88 "'\245^,\356\266\0208\270\266>\0\0\0\0\0\0'"\0
  CUR = 18
  LEN = 20
Can't find string terminator "'" anywhere before EOF at -e line 1.
[download]

Is there some way to pass the string returned by pack() to that system command ?
I assume that it ought to be possible, and that I'm just doing something dumb.

Cheers,
Rob

Comment on Re^2: pack() returns an unusable string Select or Download Code

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Re^3: pack() returns an unusable string by tybalt89 (Monsignor) on May 27, 2021 at 01:34 UTC
And here's a version with Data::Dumper and some config vars that also works. `#!/usr/bin/perl -l use strict; # https://perlmonks.org/?node_id=11133064 use warnings; my $template = 'd<'; my $nv = 2.4; $nv = 4135; # NOTE errors for this number my $p = pack $template, $nv; use Data::Dumper; $Data::Dumper::Terse = $Data::Dumper::Useqq = 1; my $s = Dumper $p; print ">$s<\n"; system $^X, '-wle', "use strict; print unpack('H*', $s);";` [download] Outputs: `>"\0\0\0\0\0'\260\@" < 000000000027b040` [download] note that it adds a newline, but perl doesn't care.	[reply] [d/l] [select]
Re^4: pack() returns an unusable string by syphilis (Archbishop) on May 27, 2021 at 02:39 UTC
And here's a version with Data::Dumper and some config vars that also works Neither this nor the rendition using Data::Dump works for me on Windows: C:\_32\pscrpt>type test3.pl use strict; # https://perlmonks.org/?node_id=11133064 use warnings; my $template = 'd<'; my $nv = 2.4; $nv = 4135; # NOTE errors for this number my $p = pack $template, $nv; use Data::Dumper; $Data::Dumper::Terse = $Data::Dumper::Useqq = 1; my $s = Dumper $p; print ">$s<\n"; system $^X, '-wle', "use strict; print unpack('H*', $s);"; C:\_32\pscrpt>perl test3.pl >"\0\0\0\0\0'\260\@" < syntax error at -e line 1, at EOF Execution of -e aborted due to compilation errors. C:\_32\pscrpt> [download] I guess it's something to do with Windows command line quoting rules. Mind you, having it work on Windows specifically is not important. Now that I have a working example, I can while away some time porting your fix to Windows when I have nothing better to do. Thanks tybalt89 !! Cheers, Rob Thanks	[reply] [d/l]
Re^5: pack() returns an unusable string by tybalt89 (Monsignor) on May 27, 2021 at 03:16 UTC
Just another guess (to tweak GrandFather) because I don't have a Windows system to test on. `#!/usr/bin/perl -l use strict; # https://perlmonks.org/?node_id=11133064 use warnings; my $template = 'd<'; my $nv = 2.4; $nv = 4135; # NOTE errors for this number my $p = pack $template, $nv; use Data::Dump qw(pp); my $s = (pp $p) =~ s/"(.)"/qq($1)/sr; # tweak for different delimiter print ">$s<\n"; system $^X, '-wle', "use strict; print unpack('H', $s);";` [download]	[reply] [d/l]
Re^6: pack() returns an unusable string by syphilis (Archbishop) on May 27, 2021 at 06:06 UTC
Re^7: pack() returns an unusable string by tybalt89 (Monsignor) on May 27, 2021 at 13:26 UTC
Re^3: pack() returns an unusable string by tybalt89 (Monsignor) on May 27, 2021 at 01:11 UTC
This seems to work :) `#!/usr/bin/perl -l use strict; # https://perlmonks.org/?node_id=11133064 use warnings; my $template = 'd<'; my $nv = 2.4; $nv = 4135; # NOTE errors for this number my $p = pack $template, $nv; use Data::Dump qw(pp); my $s = pp $p; print ">$s<\n"; system $^X, '-wle', "use strict; print unpack('H*', $s);";` [download] Outputs: `>"\0\0\0\0\0'\xB0\@"< 000000000027b040` [download]	[reply] [d/l] [select]


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