Very Computer

What is the best way to create a unique file name for temporary files?

...Mike

Quote:> What is the best way to create a unique file name for temporary
> files?

'date +%s' or using $RANDOM if your shell allows and you create  > 1
file per second or combine both.

Michael Heiming

man tempnam

HTH - Maurice

man mkstemp

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Thanks to all who answered. I finally settled on the date/time + $RANDOM.

...Mike

Quote:> What is the best way to create a unique file name for temporary files?

> ...Mike

That is not guaranteed to be unique.

In particular, in a security-critical application it can be
relatively easily predicted by a malicious attacker,
and in a heavily-used machine two processes using it might
accidentally hit on the same name ($RANDOM may well be same
for each instance of the process, so if two of them run within
same second...)

That may or may not matter in your case (like, if you are creating the
in a protected directory and you know there can't be two instances at
the same time), but if you are using a public directory like /tmp and
letting others run it, you might wish to do it more carefully.

The multiple-instance problem can be handled simply by adding
process ID ($$) to the string, but it won't help against
malicious attackers.

If your system has a working mktemp you could use it (but be
warned, quite a few mktemp's are broken and vulnerable to
attacks), otherwise here's a sample code that works with
Korn shell:

n=0
set -o noclobber
until MYTMP=/tmp/mytmp$$.$n; >$MYTMP ;do
   n=$(( n+1 ))
done 2>/dev/null
set +o noclobber

Basically that keeps incrementing the suffix number until
it finds a free filename, and then creates it in same atomic
operation, so no other process can intervene.
With POSIX-compliant shells you can achieve the same by
replacing "set -o noclobber" by "set -C" and
"set +o noclobber" by "set +C"; with other shells it may or
may not be possible, depending on availability of an
test-and-create -type atomic operation.

--
Tapani Tarvainen

Wait a minute...  How is this to be used?  Do you want a standalone
program that you can run to generate a name only?  Do have an existing
program that needs to use a temp file?

If the latter, why do you even need a file name?  You can use the
standard C function tmpfile() in stdio.h to simply return a handle to a
new, temporary file, which will close and unlink itself upon program
exit.  Check the following snippet:

#include <stdio.h>

int main(void) {
   FILE *temp = tmpfile();
    if (temp) {
       /* Do things with temp */
    }
     return 0;

Quote:}

If the former, use the standard C function tmpnam(), also in stdio.h.  It
is guaranteed to return a unique string that is not the name of an
existing file. If you want a program that will generate a unique filename
for you, go like this:

/* File:  GimmeTmpName.c */
#include <stdio.h>

int main(void) {
   printf("%s", tmpnam(NULL));
   return 0;

Quote:}

Then, when compiled, you can do things like this:
$ ./GimmeTmpName
/var/tmp/aaaeLayCl

$ ps -aef > `./GimmeTmpName`

Hope this helps,
Ryan.

Thanks, Tapani. I'm going to file your soultion for later use. A fairly
simple solution works for my current problem since I'm simply creating
temporary files from several cronned scripts which mail statistics to me.
It's in a directory which is used only for this purpose and security is not
an issue. Thanks, again.

...Mike