Does perl have an internal function to unquote a variable? -


it not uncommon parameter passed few times.

here interesting example of losing quote can helps.

the first abs() return variable without quote, making second abs return correct value.

my question is:

does perl have internal function unquote variable not have code way?

#!/usr/bin/perl -w use strict; @nums = (     '-0',     '-0.0',     "-0.000",     qw(-0.000),     sprintf("%.4f", "-0.0"), );  print "***use single abs()\n"; foreach $num(@nums){     $number = $num;     $abs = abs($number);     print "<$num> abs <$abs>\n"; }  print "\n***use abs(abs())\n"; foreach $num(@nums){     $abs_abs = abs(abs($num));     print "<$num> double abs <$abs_abs>\n"; }

system information:

uname -r 2.6.32-573.12.1.el6.centos.plus.x86_64 perl, v5.10.1 (*) built x86_64-linux-thread-multi

the screen output:

***use single abs() <-0> abs <0> <-0.0> abs <-0> <-0.000> abs <-0> <-0.000> abs <-0> <-0.0000> abs <-0>  ***use abs(abs()) <-0> double abs <0> <-0.0> double abs <0> <-0.000> double abs <0> <-0.000> double abs <0> <-0.0000> double abs <0>

that's not issue quotes -- quotes perl syntax tell interpreter string begins , ends. perl knows value being stored string, quotes not stored in memory.

rather, it's artifact of special floating point value "-0.0". use, equivalent value 0.0

perl -e ' $p = 0.0; $n = -0.0; $p == $n '                    ==> 1 perl -e ' $p = 0.0; $n = -0.0; $x = 4.2; $p+$x == $n+$x '    ==> 1

the 2 exceptions, far can tell, binary representation , string representation.

$ perl -e 'print pack "f",0.0' | od -c 0000000  \0  \0  \0  \0  \0  \0  \0  \0 0000010 $ perl -e 'print pack "f",-0.0' | od -c 0000000  \0  \0  \0  \0  \0  \0  \0 200 0000010  $ perl -mdevel::peek -e 'dump($n=-0.0),dump($p=0.0)' sv = nv(0x43523d8) @ 0x434ff00   refcnt = 1   flags = (nok,pnok)   nv = -0 sv = nv(0x43523e0) @ 0x4329b58   refcnt = 1   flags = (nok,pnok)   nv = 0  $ perl -e '$p=0.0; $n=-0.0; $p,$n' 0 -0

(actually, perl v5.12 see 0,-0 v5.16 0,0 -- maybe noticed , fixed it)

the integers 0 , -0 not have issue. abs(-0.0) returns integer 0, , accident abs appears resolve "quoting" issue.


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