cp /dev/zero filename creates large files

[Don Sharp]

Thanks to everyone that replied pointing out that it was /dev/null that
I needed NOT /dev/zero.

Thanks again

Don Sharp


"Peter J. Acklam" wrote:
> 
> Don Sharp <dwsharp@iee.org> wrote:
> 
> >I carried out the following sequence of commands
> >
> >$ for i in `cat /tmp/d`; do if [ -f $i.idx ]; then ls -l ${i}*; fi; done
> >-rw-r--r--    1 don      None            0 Jun 17  1998 dtaq
> >-rw-r--r--    1 don      None         3072 Jun 17  1998 dtaq.idx
> >$ cp /dev/zero dtaq.idx
> >
> >The cp appeared to be hanging and the disc was rattling away, so in
> >another window I typed in
> >
> >$ ls -l dtaq*
> >-rw-r--r--    1 don      None            0 Jun 17  1998 dtaq
> >-rw-r--r--    1 don      None     65307648 Jun 17  1998 dtaq.idx
> >
> >and you can see that the reported size of the target of the 'cp
> >/dev/zero' has grown to a considerable size in a short time.
> >
> >Can anyone else reproduce this?
> 
> Hopefull, everyone can reproduce this.  I think you are mixing
> /dev/zero with /dev/null.  /dev/zero will always return a buffer
> full of zeros (that is NULs, not the digit or letter zero).
> /dev/zero has infinite length, so copying from it with "cp" to
> a regular file will always cause you do run out of disk space.
> 
> Peter
> 
> --
> Peter J. Acklam - pjacklam@online.no - http://home.online.no/~pjacklam

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