bug#12366: [gnu-prog-discuss] Writing unwritable files

[Bob Proulx]

Paul Eggert wrote:
> >> If some other process is writing F
> >> while I run 'sed -i F', F is not replaced atomically.
> 
> > How not so?
> 
> For example:
> 
> echo ac >f
> sed -i 's/a/b/' f &
> sed -i 's/c/d/' f
> wait
> cat f
> 
> If 'sed' were truly atomic, then the output of this would
> always be 'bd'.  But it's not.

The file replacement is atomic.  The reading of the file is not.

Bob