Re: st: RE: -replace- should not be use with temporary files (was:Comparing datasets)

[Kevin Crow <kcrow@stata.com>]

On Thu, 18 Sep 2008, Nick Cox wrote:

This came up on the list a while back.

Suppose you mistype the local macro reference. Say you mean to type

save `myfile', replace

but you have a minute brainstorm and you type `myfil'. Further suppose
that local macro `myfil' is not defined. Then Stata sees

save, replace

which to Stata is perfectly legal and intelligible. Stata will overwrite
the original data file, which is not what you intended at all. Of
course, typos here and there can have all sorts of consequences, all of
which are strictly your fault, but this one could be catastrophic if
what you had in memory was only a small part of the data or nothing to
do with the dataset you last read in.

There may be other reasons for not doing this, but that's one.

Nick

--------------------------------------------------------------------------------

I was able to track down the email that was sent to Steven via our database and
Nick is exactly right on what happened.  What we told Steven was

        "The -replace- option shouldn't be needed when using temporary files
        because they are freshly created each time the procedure is run."

For this particular do-file the advice was correct because a temporary file was 
not getting created so the command -save `no_temp_file', replace- could be 
replacing a file on disk, not a temporary file.  In short, it is ok to use 
-replace- with temporary files but it could be dangerous.

Kevin Crow
StataCorp




> This came up on the list a while back. 
> Suppose you mistype the local macro reference. Say you mean to type 
> save `myfile', replace 
> but you have a minute brainstorm and you type `myfil'. Further suppose
> that local macro `myfil' is not defined. Then Stata sees 
> save, replace
>
> which to Stata is perfectly legal and intelligible. Stata will overwrite
> the original data file, which is not what you intended at all. Of
> course, typos here and there can have all sorts of consequences, all of
> which are strictly your fault, but this one could be catastrophic if
> what you had in memory was only a small part of the data or nothing to
> do with the dataset you last read in. 
> There may be other reasons for not doing this, but that's one. 
> Nick 
> n.j.cox@durham.ac.uk 
> Joseph Coveney
>
> Steven Samuels wrote (excerpted):
>
> . . . Technical support told me that "replace" should not be used when
> saving temporary files.
>
> ------------------------------------------------------------------------
> --------
>
> This is news to me.  I use -replace- all of the time with temporary
> files.
> What did StataCorp technical support say was the matter with using
> -save . . . , replace- with temporary files?
>
>
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