How to reverse for each 2 character ?

bh_perl has asked for the wisdom of the Perl Monks concerning the following question:

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Re: How to reverse for each 2 character ? by Corion (Patriarch) on Aug 29, 2008 at 07:20 UTC
Read pack. Likely you're using the `H2` template and it seems you want to use the `h2` template instead.	[reply] [d/l] [select]
Re: How to reverse for each 2 character ? by ikegami (Patriarch) on Aug 29, 2008 at 07:41 UTC
Sounds like you chose the wrong one of `unpack('V', $packed)`, `unpack('N', $packed)` and `unpack('L', $packed)`. `printf "%08X\n", unpack 'N', "\x12\x34\x56\x78"; # 12345678 printf "%08X\n", unpack 'V', "\x12\x34\x56\x78"; # 78563412` [download]	[reply] [d/l] [select]
Re^2: How to reverse for each 2 character ? by bh_perl (Monk) on Aug 29, 2008 at 08:05 UTC
is it right command ? `my $cdrdata = unpack "N*", substr($data, BLOCKHDR+BLOCKDATA, CDRLENGT +H);` [download] Its look not convert all the hex values, might be my code is wrong..	[reply] [d/l]
Re^3: How to reverse for each 2 character ? by gone2015 (Deacon) on Aug 29, 2008 at 08:47 UTC
`unpack "N", $string` will take the first 4 bytes of `$string` and return a 32-bit integer, taking the 4 bytes in "Network" order -- the first byte is the most significant, and then in descending order (ie big-endian). `unpack, "N", $string` will repeat the process of extracting 32-bit integers to consume all of `$string`, and returns a list of those integers. `my $cdrdata = unpack "N", $string` will unpack as many 32-bit integers as there are in `$string`, and then set `$cdrdata` to the first of them. Which, on the face of it, isn't what you wanted. If the input is little-endian, you need `unpack "V", ...`. If the input is not 32-bit integers in one or other order, you need something more general, such as: `my $foo = reverse(unpack('h', "\x21\x43\x65\x87\x09\xBA\xDC")), "\n +" ;` [download] which sets `$foo` to the string: `1234567890abcd` You can, of course, replace the `` in `h` by a number to extract a fixed number of bytes. So `'(h6)'` would extract six bytes at a time, as many times as it could. I'll leave why this works as homework :-)	[reply] [d/l] [select]
Re^3: How to reverse for each 2 character ? by ikegami (Patriarch) on Aug 29, 2008 at 08:09 UTC
No idea. I don't know the format of your data.	[reply]
Re: How to reverse for each 2 character ? by moritz (Cardinal) on Aug 29, 2008 at 07:20 UTC
`$ perl -wle 'print join "", reverse unpack("(A2)*", "1234567890")' 9078563412` [download] Or you could `scalar reverse` the binary data before unpacking it, that should give the same result.	[reply] [d/l] [select]