Validate File Types by Reading the First Few Bytes of a File

Quickly check if a file is a jpg, png, etc.. We'll use the od command line tool or Python / Ruby.

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0:00 -- Intro
0:16 -- File types typically have well known starting bytes
0:51 -- All 3 ways will be constant time O(1)
1:15 -- Using the od (octal dump) built-in command
4:52 -- Constant vs linear time with getting the last bytes
8:57 -- Python version
11:54 -- Ruby version
15:19 -- Using a library to help detect file types

[adrianbiro]

file command is useful one, but when you need to see the details and then manually check it, your solution looks nice.

[yomajo]

This was interesting, thanks!
P.s. I prefer "head -1" over "head -n 1".

[samoylov]

xxd image.png | head -1 | cut -d\ -f2
will give us the same numbers.
Peculiar thing is code (the other way around) also works:
cut -b -2 afisha.png | head -1 | xxd
(and it is even colored one) - cut can work with bytes

[uxjkdkn]

the magic number if I am not mistaken.