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Programatically find out a file type by looking its binary content. Possible?

Answer 1

A:

On linux, there is a command called file. Given an arbitrary file, it attempts to determine what kind of file it is. For instance:

gzip compressed data, from Unix, last modified: Fri Jun 12 20:16:28 2009
HTML document text
vCalendar calendar file
RCS/CVS diff output text

Those are from a few random files lying around my home directory.

retracile 2010-05-27 13:48:26

Im working on a .net component that will be deployed on a windows environment.

2010-05-27 14:00:58

Answer 2

A:

Yep. See file.

And please do not reinvent the wheel. It works just fine how it is.

amphetamachine 2010-05-27 13:48:51

Of course this particular wheel works under Linux. Not the common platform to target with c#.

Jens 2010-05-27 13:50:38

@Jens - It's cross-platform, actually. Not the sort of platform to target with C#.

amphetamachine 2010-05-27 13:51:46

Thanks Jens, I was looking at something like a file signature for each of those types I mentioned.

2010-05-27 14:00:22

Answer 3

+4 A:

On Linux/Unix based systems you can use the file command, but I assume you want to do this manually yourself in code...

If all you have access to is the byte stream of the file, then you would need to handle each file type independently.

Most programs/components that do what you are wondering usually read the first few bytes and make a classification based on that. For example GIF files start with one of the following: GIF87a or GIF89a

Many file formats have the same signature at the start of the file, or have the same header format. This signature is refered to as a magic number as described by me on this post.

A good place to get started is to go to www.wotsit.org. It contains the file format specifications searchable by file type. You could look at the important file types that you want to handle and see if you can find some identifying factor in those file formats.

You could also search Google to try and find a library that does this classification, or look at the source code of the file command.

Brian R. Bondy 2010-05-27 13:48:52

Thanks. will look into this

2010-05-27 14:01:23

If you want to handle in code, yeah your only options is to look at the bytes and figure out what the file type is based on that. Most files have some kind of header in the first few bytes describing the data, format, etc.

Justin 2010-05-27 15:50:07

Answer 4

+1 A:

You maybe interested in this: http://en.wikipedia.org/wiki/Magic_number_(programming)

Most binary formats contain a magic number at their beginning. If you only have to recognize a certain set of formats, it should be easy to check the first few bytes of a new incoming file and guess the appropriate file extension correctly.

xor_eq 2010-05-27 13:53:34

Thanks, but the magic number seems to be the same across all MS Office files (doc,xls,rtf). I need to differentiate between these as well.

2010-05-28 08:57:08

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Programatically find out a file type by looking its binary content. Possible?

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