Re: unusual uniq results

[Stone <xstonedogx@gmail.com>]

The redirection takes place before your command.  So basically what
you told the system to do was:

1.  Create the file dup_num.  If the file exists overwrite it.
2.  Redirect stdout of "uniq dup_num" into dup_num.

Since you'd already overwritten the data in dup_num, there was nothing
for uniq to process.

On Tue, 28 Sep 2004 11:09:12 -0400, William Stanard
<wstanard@palmertrinity.org> wrote:
> In doing a demo before a class (Linux Red-hat 2.4.18-14), I used the uniq
> command on a file (dup_nums) that consisted of twelve lines, each line
> containing a number, from one to 9. I repeated the numbers, 6, 8, and 9.
> The std output showed the expected list of numbers, all duplicates
> removed. At a student's suggestion, I ran uniq again, but this time
> directed the output to the file itself....
> 
> uniq dup_num > dup_num
> 
> ...and, lo and behold, the file dup_num was empty. I checked uniq --help,
> info uniq, and man uniq, all to no avail. Shouldn't uniq have removed the
> duplicate numbers and written one through 9 to the file?
> 
> Bill stanard
> 
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