Re: perl hex possible bug
On Tue, Jul 21, 2020 at 3:12 PM Edgar Pettijohn
wrote:
> I was playing around with the hex function in perl. So naturally I
> started with:
>
> perldoc -f hex
>
> Which showed me a few examples namely the following:
>
> print hex '0xAf'; # prints '175'
> print hex 'aF'; # same
> $valid_input =~ /\A(?:0?[xX])?(?:_?[0-9a-fA-F])*\z/
>
> However, I get the following output: (newlines added for clarity)
>
> laptop$ perl -e 'print hex '0xAf';'
> 373
>
You used the same quotes on the inside and out, so the "inner"
quotes actually never get to the perl! The shell parses the argument to
perl to
print hex 0xAf
0xAf is a numeric literal whose value is 175. The hex() function then
takes its argument (175) converts it to a string ("175") and interpretats
that string per its rules...as if you passed it "0x175" which equals 373.
If you use distinct quotes, you get the value you expect:
$ perl -le 'print hex "0xAf";'
175
$
> laptop$ perl -e 'print hex 'aF';'
> 175
>
That relies on the so-called poetry extension, where a bare word like aF is
treated as a string. Turn on strict...
$ perl -Mstrict -le 'print hex Af;'
Bareword "Af" not allowed while "strict subs" in use at -e line 1.
Execution of -e aborted due to compilation errors.
$
> I'm guessing there is a bug here but not sure if its software or
> documentation.
>
No bug, just shell quoting traps.
Philip Guenther
Re: perl hex possible bug
I realized after the fact, that looking at some of the different ways you can write numbers in perl. $n = 1234; # decimal integer $n = 0b1110011; # binary integer $n = 01234; # octal integer $n = 0x1234;# hexadecimal integer $n = 12.34e-56; # exponential notation $n = "-12.34e56"; # number specified as a string $n = "1234";# number specified as a string http://man.openbsd.org/perlnumber On Tue, Jul 21, 2020 at 05:24:34PM -0700, Andrew Hewus Fresh wrote: > On Tue, Jul 21, 2020 at 07:10:34PM -0500, Edgar Pettijohn wrote: > > I was playing around with the hex function in perl. So naturally I > > started with: > > > > perldoc -f hex > > > > Which showed me a few examples namely the following: > > > > print hex '0xAf'; # prints '175' > > print hex 'aF'; # same > > $valid_input =~ /\A(?:0?[xX])?(?:_?[0-9a-fA-F])*\z/ > > > > However, I get the following output: (newlines added for clarity) > > > > laptop$ perl -e 'print hex '0xAf';' > > 373 > > so, you're double-use of single quotes here causes some fun shell > processing. This is the same as: > > perl -e 'print hex 0xAf' > > (although let me re-do that with -E and say) > > $ perl -E 'say hex 0xAf' > 373 > > Well, as you say, that's not what you expect. > > But, perhaps there is an explanation. Lets try without hex. > > $ perl -E 'say 0xAf' > 175 > > interesting, but where's the hex? > > $ perl -E 'say hex 175' > 373 > > ahh, there it is. > > Just to get back on the original page though and avoid the shell > confusion, lets try one last thing. > > $ perl -E 'say hex "0xAf"' > 175 > > And that work. Although I guess we can also > > $ perl -e 'print hex "0xAf"' > 175 > > if you'd like. > > > > laptop$ perl -e 'print hex 'aF';' > > 175 > > > > I'm guessing there is a bug here but not sure if its software or > > documentation. > > > > Thanks, > > > > Edgar > > > > -- > andrew - http://afresh1.com > > Hey! It compiles! Ship it! > -- andrew - http://afresh1.com Hey, I think I see a barn up ahead. -- The American Astronaut
Re: perl hex possible bug
On Tue, Jul 21, 2020 at 07:10:34PM -0500, Edgar Pettijohn wrote: > I was playing around with the hex function in perl. So naturally I > started with: > > perldoc -f hex > > Which showed me a few examples namely the following: > > print hex '0xAf'; # prints '175' > print hex 'aF'; # same > $valid_input =~ /\A(?:0?[xX])?(?:_?[0-9a-fA-F])*\z/ > > However, I get the following output: (newlines added for clarity) > > laptop$ perl -e 'print hex '0xAf';' > 373 so, you're double-use of single quotes here causes some fun shell processing. This is the same as: perl -e 'print hex 0xAf' (although let me re-do that with -E and say) $ perl -E 'say hex 0xAf' 373 Well, as you say, that's not what you expect. But, perhaps there is an explanation. Lets try without hex. $ perl -E 'say 0xAf' 175 interesting, but where's the hex? $ perl -E 'say hex 175' 373 ahh, there it is. Just to get back on the original page though and avoid the shell confusion, lets try one last thing. $ perl -E 'say hex "0xAf"' 175 And that work. Although I guess we can also $ perl -e 'print hex "0xAf"' 175 if you'd like. > laptop$ perl -e 'print hex 'aF';' > 175 > > I'm guessing there is a bug here but not sure if its software or > documentation. > > Thanks, > > Edgar > -- andrew - http://afresh1.com Hey! It compiles! Ship it!
perl hex possible bug
I was playing around with the hex function in perl. So naturally I started with: perldoc -f hex Which showed me a few examples namely the following: print hex '0xAf'; # prints '175' print hex 'aF'; # same $valid_input =~ /\A(?:0?[xX])?(?:_?[0-9a-fA-F])*\z/ However, I get the following output: (newlines added for clarity) laptop$ perl -e 'print hex '0xAf';' 373 laptop$ perl -e 'print hex 'aF';' 175 I'm guessing there is a bug here but not sure if its software or documentation. Thanks, Edgar
