Casting return value of unpack properly

I am using unpack to unpack an element that consists of a 32 byte hex string plus an optional unsigned integer. If the integer exists, I want to join the 2 with an underscore.

I tried:

join("_", unpack("H32V*", $string));
[download]

but it always performs the join even if there is no second element. Adding an intermediate assignment, made it work:

my @temp = unpack("H32V*", $string);
join("_", @temp);
[download]

But that seems kludgy and I would like to avoid it. So, is there any way to properly cast/assign the result of unpack so that an undefined second element is ignored by join without using an intermediate variable?

Comment on Casting return value of unpack properly Select or Download Code
Re: Casting return value of unpack properly by jethro (Monsignor) on Feb 12, 2013 at 16:00 UTC
I got the following results with perl v5.14.2: `my $string="1234567812345678"; print join("_", unpack("H32V", $string)),"\n"; my @temp = unpack("H32V", $string); print join("_", @temp),"\n"; $string="12345678123456781111"; print join("_", unpack("H32V", $string)),"\n"; @temp = unpack("H32V", $string); print join("_", @temp),"\n"; #prints: 31323348355037383132333435363738 31323348355037383132333435363738 31323334353637383132333435363738_825307441 31323334353637383132333435363738_825307441` [download] As you can see, no difference between the two forms	[reply] [d/l]
Re^2: Casting return value of unpack properly by puterboy (Beadle) on Feb 12, 2013 at 16:39 UTC
You are correct... I'm not sure what changed but I could have sworn it wasn't working before....	[reply]
Re^2: Casting return value of unpack properly by mbethke (Hermit) on Feb 12, 2013 at 16:53 UTC
Edit: whistle	[reply]
Re: Casting return value of unpack properly by Anonymous Monk on Feb 12, 2013 at 16:00 UTC
You could always throw in a quick `grep {defined $_}` to filter them out.	[reply] [d/l]
Re: Casting return value of unpack properly by AnomalousMonk (Prior) on Feb 12, 2013 at 16:33 UTC
... it always performs the join even if there is no second element. By this, I think you mean that there is a `'_'` present in all cases, even if it the last (and dangling) character in the `unpack`-ed string. I tried essentially the same code as jethro under ActiveState 5.8.9 and Strawberries 5.10.1.5, 5.12.3.0 and 5.14.2.1 and get no extraneous underscore. `>perl -wMstrict -le "my $p = 'ABCDabcdABCDabcd' . pack 'V', 0x3039; print qq{'$p'}; ;; my $unp = join '_', unpack 'H32V', $p; print qq{'$unp'}; ;; $p = 'ABCDabcdABCDabcd'; print qq{'$p'}; ;; $unp = join '_', unpack 'H32V', $p; print qq{'$p'}; " 'ABCDabcdABCDabcd90 ' '41424344616263644142434461626364_12345' 'ABCDabcdABCDabcd' 'ABCDabcdABCDabcd'` [download] Can you supply a short, stand-alone code example that demonstrates the effect you seek to avoid?	[reply] [d/l] [select]
Re^2: Casting return value of unpack properly by puterboy (Beadle) on Feb 12, 2013 at 16:41 UTC
I can't replicate it now. Perhaps before I was using 'B' or 'A' instead of 'V*'... but not sure what happened. I apologize for taking your time on what seems to be a non-issue.	[reply]
Re^3: Casting return value of unpack properly by AnomalousMonk (Prior) on Feb 12, 2013 at 17:12 UTC
Oh, well... Just one of those days... sigh	[reply]


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Casting return value of unpack properly

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