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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: sizeof environment variables array = 1?
Date: Fri, 09 Jun 2017 08:41:54 -0700
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DFS <nospam@dfs.com> writes:
> On 6/8/2017 6:12 PM, Keith Thompson wrote:
>> Instead, I strongly suggest you define what constitutes valid input
>> for your program, and check for that.
>
> 'file' returns ASCII in the description, or the extension is .txt.
>
> That's it.

I don't believe the file command reads the entire file, so it might
report ASCII for something that contains non-ASCII characters.

On systems that support symbolic links, "file" on a symbolic link
just says it's a symbolic link; it doesn't report on the contents
of a file.  I would expect a symlink to a pure ASCII text file to
be acceptable, but you would reject it.  Unless the target of the
symlink happens to have the string ASCII in its name.

I can rename any binary file to give it a ".txt" extension.  If your
program is vulnerable to bad input, that's how someone can break it.

If those are your requirements, that's up to you -- but I don't
see how the requrements you've given make any sense.

There must be some logical basis for the requirements you've
stated, but if you're unwilling to discuss that basis (your *real*
requirements), we can't help you.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"