How to output binary files in Perl?

Question

I want to be able to output 0x41, and have it show up as A.

This is what I have tried so far:

my $out;
open $out, ">file.txt" or die $!;
binmode $out;
print $out 0x41;
close $out;

It outputs 65 instead of A in the resulting file. This is not what I want.

I also have read this similar question, but I wouldn't transfer the answer over. pack a short results to 2 bytes instead of 1 byte.

I think the most important hint in the perldoc of print is: Prints a string or a list of strings. ... and not numbers. That's why the binary mode of the file handle (although needed for binary data!) is a red herring regarding the binary interpretation. I have also fallen into this trap. — MattTT
– MattTT, Commented Jun 20, 2022 at 10:52

Amadan · Accepted Answer · 2012-11-29 06:00:11Z

3

You can use chr(0x41).

For larger structures, you can use pack:

pack('c3', 0x41, 0x42, 0x43) # gives "ABC"

Regarding your suspicion of pack, do go read its page - it is extremely versatile. 'c' packs a single byte, 's' (as seen in that question) will pack a two-byte word.

edited Nov 29, 2012 at 6:00

answered Nov 29, 2012 at 5:54

Amadan

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2 Comments

Amadan Over a year ago

AFAIK, chr will work for any byte value (0-255). It has a bit more complex relationship to Unicode. Still, pack is quite reliable, as you can tailor the template to what you need.

MattTT Over a year ago

consider to use pack('C', ...). Otherwise for values above 0x7f there is a warning "Character in 'c' format wrapped in pack" (although the output is correct).

Guru · Accepted Answer · 2012-11-29 05:53:39Z

1

Use the chr function:

print $out chr 0x41

answered Nov 29, 2012 at 5:53

Guru

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Comments

F. Hauri - Give Up GitHub · Accepted Answer · 2012-11-29 06:20:33Z

1

pack need two argument: The first argument explain how and how many data have to be packed:

perl -e 'printf "|%s|\n",pack("c",0x41,0x42,0x44);'
|A|

perl -e 'printf "|%s|\n",pack("c3",0x41,0x42,0x44);'
|ABD|

perl -e 'my @bytes=(0x41,0x42,0x43,0x48..0x54);
         printf "|%s|\n",pack("c".(1+$#bytes),@bytes);'
|ABCHIJKLMNOPQRST|

you could even mix format in the 1st part:

perl -e 'printf "|%s|\n",pack("c3B8",0x41,0x42,0x44,"01000001");'
|ABDA|

answered Nov 29, 2012 at 6:20

F. Hauri - Give Up GitHub

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