Web lists-archives.com

Re: searching non plain text files




On Sun, 16 Dec 2018 20:16:08 -0500, John wrote:
> On Sun, 2018-12-16 at 14:33 -0500, Tedd Sperling wrote:
>> > On Dec 14, 2018, at 11:19 PM, Jeffry Killen <jekillen@xxxxxxxxxxx> wrote:
>> > 
>> > 
>> > Can anyone point me to instruction/advice about
>> > opening and reading files that are not plain text:
>> 
>> Jeffry:
>> 
>> I don’t know if this will help you, but most “honest” files have a header that
>> states what it is.
>> 
>> Try using a hex-editor app and observing the first 10 characters in their
>> headers (i.e., start of the file). For example, a PDF file will state ‘PDF’, a
>> jpg will state ’JFIF’, a rtf file will state ‘rtf’, a zip file will state
>> ‘PK”, a png will state ‘PNG”, and so on.
>> 
>> From that observation, you might try working with bin2hex or dechex and other
>> such bin/hex functions PHP provides to check what the file type is in the
>> header and what it reports itself to be in the extension. 
>> 
>> Additionally, you can always Google it.
>> 
> Just to confuse the issue, both zip files and odt (Open Document) files have the
> 'PK' header id.  Looking around for some other formats, I found that most tgz
> files (tar, gzipped) have 'vV' followed by the file name (but not all of them!).
> So Jeffry will have to do some sort of a secondary test to be sure.

Do a search on "magic bytes".

Jonesy
-- 
  Marvin L Jones    | Marvin      | W3DHJ.net  | linux
   38.238N 104.547W |  @ jonz.net | Jonesy     |  FreeBSD
    * Killfiling google & XXXXbanter.com: jonz.net/ng.htm