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Old 02-07-2013, 04:10 PM   #1
nicnicman
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What type of file is hash?


For a homework question I was asked "What type of file is 'hash'?" But, isn't hash a command?

Btw, we're allowed to seek help on the assignment.

Thanks for any suggestions.
 
Old 02-07-2013, 04:33 PM   #2
ted_chou12
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From my knowledge based on Java, hash is a integer that can be generated from a file. Hash allows you to compare if two files are NOT equal, and gives you a swift retrieval of files. Anyone correct me if i am not wrong.
 
Old 02-07-2013, 04:35 PM   #3
Ser Olmy
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The question doesn't really make sense. Does it appear in a particular context?

A hash is a cryptographic signature of some data, created using a one-way algorithm. The length of the hash depends on the algorithm being used.

I've never heard of a file type called "hash".
 
Old 02-07-2013, 06:23 PM   #4
nicnicman
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The question is a separate question by itself without any other context. It is as I wrote it between the double quotes.

Is there a file named 'hash'?

Thanks for the suggestions.
 
Old 02-07-2013, 06:31 PM   #5
chrism01
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There's no file type of hash.

Hash can be:

1.
Quote:
cryptographic signature of some data, created using a one-way algorithm
as per Ser Olmy.
Also the verb to do.

2. An indexed data structure ie a set of: key => value pairs.
The key can be any (reasonable) string (inc integer) eg prob not using ctrl chars etc.
In the Perl lang a hash is a basic var type eg http://www.perlmonks.org/?node_id=471590
NB: these are known in some langs as 'associative arrays' even as a 'map' in some cases.
EG in php, 'arrays' are really of the associative type, rather than the traditional eg C, Perl integer indexed style
http://www.php.net/manual/en/function.array.php

3. Of course, you can save a hash (of type 2) to disk eg in Perl a Tied::Hash and this would be a file in hash table format; that's probably(?) what the qn means...

HTH

Last edited by chrism01; 02-07-2013 at 06:33 PM.
 
Old 02-07-2013, 07:18 PM   #6
grail
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Actually the OP has asked 2 different questions so it may be prudent to ask which is correct:

"What type of file is 'hash'?" post #1

Is there a file named 'hash'? post #4

The second would lead me to believe you are supposed to find if a file 'named' "hash" in a particular location


Please clarify?
 
Old 02-07-2013, 07:41 PM   #7
nicnicman
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The question as given by my instructor is the first one:

"What type of file is 'hash'?"

To me, the question seems like it's saying there is a file named hash and then asking what type of file is hash. That's why I asked if there was a file named hash so I could then proceed to find what type of file it is, if it did indeed exist.

It's not asking what kind of file type is hash, it's asking what kind of file is hash. Make sense? Hopefully, because I'm lost.

Last edited by nicnicman; 02-07-2013 at 07:43 PM.
 
Old 02-07-2013, 08:26 PM   #8
shivaa
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@nicnicman::
Before answering to your question, let's know what is hash? In UNIX you can find kind of file or kind of file type (though both sounds same at the end), using file command:-
Code:
~$ file <filename>
For example:-
Code:
~$ file hash
hash:           cannot open: No such file or directory
So the first question is that, is there any file named 'hash' exists? If it exists, you can use file to check it's kind, else not.

Moreover, once go through Unix file types, which explains file type in Unix in details.

On the other hand, just a guess, the "#" symbol is also called 'hash' and frequently used in UNIX. So make sure that your concern is a file named 'hash', not the symbol "#".

Last edited by shivaa; 02-07-2013 at 08:32 PM. Reason: Typo
 
Old 02-07-2013, 08:38 PM   #9
chrism01
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@OP: see my previous response.

As per above comments, you can have a file whose name is 'hash', you can even have a file whose name is '#', but neither of these are std files on a *nix system (especially '#' !).
(NB: if he expects you to check a system that he's setup with a file with one of those names, that's different.
In that case, use the 'file' cmd as above)

In other words, your instructor's qn is vague (although he may not mean it to be).
I'd collect all the possible answers here and send them to him; maybe you'll get bonus pts
 
Old 02-07-2013, 09:18 PM   #10
nicnicman
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Quote:
Originally Posted by chrism01 View Post
@OP: see my previous response.

As per above comments, you can have a file whose name is 'hash', you can even have a file whose name is '#', but neither of these are std files on a *nix system (especially '#' !).
(NB: if he expects you to check a system that he's setup with a file with one of those names, that's different.
In that case, use the 'file' cmd as above)

In other words, your instructor's qn is vague (although he may not mean it to be).
I'd collect all the possible answers here and send them to him; maybe you'll get bonus pts
Where using our own systems so it's not a file he put on the system. Thanks for all the suggestions. As you say, I'll bundle them up and ask him about it.
 
Old 02-07-2013, 09:24 PM   #11
jpollard
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One alternate description is a "dictionary file". The original UNIX spell utility would split off prefixes and suffixes, then generate a hash of the root word. If the bit corresponding to the integer hash value was set in the dictionary file, then the word was properly spelled. If the bit was clear, then it is misspelled. Doesn't help much for fixing (that took additional work and a recheck), but it is a very fast check, making good use of sparse files (the dictionary file length might have been several hundred MB, but only occupy a couple of hundred blocks.
 
Old 02-08-2013, 06:46 AM   #12
linosaurusroot
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A "tied hash" as used in Perl is a Berkeley DB (or similar) file also being used as a Perl hash data type.
 
Old 02-08-2013, 08:47 AM   #13
schneidz
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maybe they are referring to some kind of ascii-txt file which contains some hash key information (md5sum/sha-1/id_dsa.pub/id_rsa.pub) ?

Last edited by schneidz; 02-08-2013 at 08:48 AM.
 
Old 02-09-2013, 01:41 PM   #14
vikky
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there is no file called hash in unix
 
  


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