Re: Writing the elements of an array to a file

The shortest and most effective way is to use a quantifier in pack:

print {$FILE} pack 'C4', @arr;
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You should have thought of a loop at least:

print {$FILE} pack 'C', $_ for @arr;
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Update: If you need pack, the array doesn't contain binary data. It contains the numbers.

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Re^2: Writing the elements of an array to a file
by bontchev (Sexton) on Aug 31, 2015 at 15:46 UTC

Thanks!

Using a quantifier did the trick; I didn't know that using pack() this way was possible.

The documentation suggests that the quantifier should be surrounded by square brackets, as in pack ("C[4]", @arr)? I guess it doesn't matter.

Not sure I understand your remark about the binary data. The elements are the result of some bit-wise operations on data. Perl keeps them in its internal representation of numbers; I just want them output as binary data (bytes). If I don't use pack(), Perl just outputs them as it would output any number by default - as a decimal number in ASCII format, which isn't what I want.

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Re^3: Writing the elements of an array to a file

by Athanasius (Archbishop) on Aug 31, 2015 at 15:56 UTC

Hello bontchev,

The documentation suggests that the quantifier should be surrounded by square brackets...

Not really. From pack (emphasis added):

The following rules apply:

Each letter may optionally be followed by a number indicating the repeat count. A numeric repeat count may optionally be enclosed in brackets, ...

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^3: Writing the elements of an array to a file

by AnomalousMonk (Archbishop) on Aug 31, 2015 at 17:22 UTC

It's also possible to use '*' as a quantifier to pack/unpack whatever number of the specified data type happens to be present:

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my $p = pack 'C*', (65, 66, 0x43, ord('D'), 0b01000101);
 print qq{'$p'};
 ;;
 my @u = unpack 'C*', $p;
 dd \@u;
"
'ABCDE'
[65 .. 69]
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Give a man a fish: <%-{-{-{-<

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Re^3: Writing the elements of an array to a file

by choroba (Cardinal) on Aug 31, 2015 at 15:55 UTC

print "\x45" | "\x59"; # Prints \x5d.
print 'E'    | 'Y';    # Same as the above, prints ].
print 69     | 89;     # Prints 93 (5d in hex).
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| is clever, it knows whether it operates on bytes (strings) or numbers.

Update: fixed typo (s/78/89/), thanks poj.

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