The problem is that the i template needs at least 32 bits, but you're only giving it 8. The $size argument to bin2dec should be 32, but even then your function won't always work depending on the endianness of your system!

$ perl -wMstrict -le 'print unpack("B*",pack("i",3))'
00000011000000000000000000000000
$ perl -wMstrict -le 'print unpack("i",pack("B*",
  "00000011000000000000000000000000"))'
3
$ perl -wMstrict -le 'print unpack("i",pack("B*",
  "00000000000000000000000000000011"))'
50331648
$ perl -wMstrict -le 'print unpack("i",pack("B*","00000011")).""'
Use of uninitialized value in concatenation (.) or string at -e line 1
+.
$ perl -wMstrict -le 'print unpack("c",pack("B*","00000011"))'
3

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(Note the use of "B*" instead of "B$size".) Some more general observations:

The i template is system-dependent. Unless the binary data itself is system-dependent, such as from C structs, I'd only use the system-independent formats, in this case for example the cCnNvV formats since those have a fixed size and endianness.

You say want to use i, but then only want handle 8 bits, that does not go together - why not use c to begin with? Also, you're not checking that your values will actually fit in 8 bits!

Lastly, I suspect you've got an XY Problem and you might want to explain to us what you're trying to accomplish overall. Don't worry about asking too many questions, but I would suggest you play around with pack and unpack a bit more, like I did above!

In reply to Re: pack and unpack with 8 bit integers by Anonymous Monk
in thread pack and unpack with 8 bit integers by thanos1983

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