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I wrote something that I think parses bits from a file, but now I need to test it. I'd like to create a file that I know has bits in a certain order. Something like:

000010000000000000000000000100000

Then I can use this file to test by bit parser, so I can tell it to grab bits 0-4 (ordered left to right) and expect it to return 00001 and then grab bits 26-31 and expect it to return 100000

How can I create a file like this in osx?

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    use a Hex editor to create the file. that way you get actual binary data instead of encoded text that consists of 1 and 0 characters. a web search for osx hex editor turns up quite a few options. Depending on your choice of products, you may have to enter the data in Hex, but that will still result in a binary file. Also, I would recommend that in general you perform your operations in bytes rather than nibbles, as you will have more compability with existing program runtimes and langague features.
    – Frank Thomas
    Dec 4, 2015 at 23:04

1 Answer 1

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You can use the printf command for it.

To get your example 0000 1000 0000 0000 0000 0000 0001 0000 do:

$ printf "\x08\x00\x00\x10" > file1
$ hexdump file1
00000000  08 00 00 10                                   |....|
00000004

Note that your example is 33 bits, I've used the first 32 bits of it.

If you want a bit more variation, try:

$ echo -n "aC3@hLp-" > file2
$ hexdump -C file2
00000000  61 43 33 40 68 4c 70 2d                           |aC3@hLp-|
00000008

Every file is a 'binary' file. The only difference between, for example, an ASCII text file and a binary file is that the range of the values of the bytes in a text file are limited to the ASCII characters. The same is true for any other encoding (e.g. Unicode UTF-8 or UTF-16).

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