How can I convert hex strings into numbers in Perl?

Question

I recently wrote a script which parsed a text representation of single binary byte month field.

(Don't ask :-{ )

After fiddling with sprintf for a while I gave up and did this;

our %months = qw / x01 1 
       x02 2
       x03 3 
       x04 4 
       x05 5 
       x06 6 
       x07 7 
       x08 8 
       x09 9 
       x0a 10 
       x0b 11 
       x0c 12 /;
...
my $month = $months{$text};

Which I get away with because I'm only using 12 numbers, but is there a better way of doing this?

Answer 1

See hex and/or oct.

#!/usr/bin/perl

use strict;
use warnings;

my @months = map hex, qw/x01 x02 x03 x04 x05 x06 x07 x08 x09 x0a x0b x0c/;
print "$_\n" for @months;

Answer 2

if you have

$hex_string = "0x10";

you can use:

$hex_val = hex($hex_string);

And you'll get: $hex_val == 16

hex doesn't require the "0x" at the beginning of the string. If it's missing it will still translate a hex string to a number.

You can also use oct to translate binary, octal or hex strings to numbers based on the prefix:

• 0b - binary
• 0 - octal
• 0x - hex

Answer 3

If I understand correctly you have 1 byte per month - not string "0x10", but rather byte with 10 in it.

In this way, you should use unpack:

my $in = "\x0a";
print length($in), "\n";
my ($out) = unpack("c", $in);
print length($out), "\n", $out, "\n"

output:

1
2
10

If the input are 3 characters, like "x05", then changing is also quite simple:

my $in = "x0a";
my $out = hex($in);