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in reply to pack() returns an unusable string
From your warning message, 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.
Try looking at a dumped wersion of $p.
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Re^2: pack() returns an unusable string
by syphilis (Archbishop) on May 27, 2021 at 00:32 UTC
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I would guess that your packed string '$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);";
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.
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.
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.
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.
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
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#!/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);";
Outputs:
>"\0\0\0\0\0'\260\@"
<
000000000027b040
note that it adds a newline, but perl doesn't care.
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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>
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
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#!/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);";
Outputs:
>"\0\0\0\0\0'\xB0\@"<
000000000027b040
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Re^2: pack() returns an unusable string
by GrandFather (Saint) on May 26, 2021 at 22:30 UTC
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Guessing is sometimes fine, but the OP gave an entire and complete test script which you can examine and even run. If I make a small modification to the test script given we can test the theory:
# test.pl
use warnings;
$template = 'd<';
$nv = 2.4;
$p = pack $template, $nv;
$s = "'$p'";
print ">$s<\n";
system $^X, '-wle', "print unpack('H*', $s);";
prints:
>'333333@'<
3333333333330340
running a 64 bit build of 5.32. Note that there is an ETX character between the final 3 and the @ character, which, when you think about it, is the string that the unpack is showing us so for the success case there is a trailing @ and it isn't swallowing the trailing '.
Optimising for fewest key strokes only makes sense transmitting to Pluto or beyond
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OP said error only happens on D<, not d<, which doesn't run on my machine.
However, here is a number for which the error occurs on 5.32 with d<
#!/usr/bin/perl -l
use strict;
use warnings;
my $template = 'd<';
my $nv = 2.4;
$nv = 4135; # NOTE errors for this number
my $p = pack $template, $nv;
my $s = "'$p'";
print ">$s<\n";
system $^X, '-wle', "print unpack('H*', $s);";
Outputs:
>''°@'<
Can't find string terminator "'" anywhere before EOF at -e line 1.
which shows that my guess that the pack produces a single quote character is plausible.
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In blead, it runs with D< and fails with
Can't find string terminator "'" anywhere before EOF at -e line 1.
However, when I tried to output
say join ', ', map ord, split //, $p;
I got
0, 152, 153, 153, 153, 153, 153, 153, 0, 64, 0, 0, 0, 0, 0, 0
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
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