PERL Beginners - Preventing shell redirection from creating empty file

Author

Preventing shell redirection from creating empty file

Dan Fish

2004-10-27, 8:55 am

I appologize that this is more of a shell question (tcsh) than a perl
question, but I've found that most of the really good perl guru's are fairly
decent shell wizards as well :-)

I have a c-routine that calls a perl script something like this:

system("myscript.pl arg1 arg2 > myfile.txt");

What is the easiest way to prevent "myfile.txt" from being created if the
script dies or produces no output? (It seems the shell will always create
myfile.txt, regardless)

I can think of a couple of ways offhand...

1. Within the c-routine, check for an empty file after the script is run
and remove if empty.
2. Handle the output directly from within the perl script with
open/print/close (I.E. avoid redirection)

I was hoping some shell guru out there knows a more generic approach.

Thanks,
-Dan

---
Dan Fish - seadancr@cox.net
"A -good- dive buddy will be there if you run out of air, a -great- one will
be there before you run out!"

Chris Devers

2004-10-28, 3:57 pm

On Tue, 26 Oct 2004, Dan Fish wrote:

> system("myscript.pl arg1 arg2 > myfile.txt");
>
> What is the easiest way to prevent "myfile.txt" from being created if
> the script dies or produces no output? (It seems the shell will always
> create myfile.txt, regardless)

Would it be enough to just delete the file if it's empty?

du myfile.txt | grep '^0' && rm myfile.txt

That seems easier than any other approach i can think of.

--
Chris Devers

Jim

2004-10-29, 8:55 am

>
> On Tue, 26 Oct 2004, Dan Fish wrote:
>
> created if
> will always
>
> Would it be enough to just delete the file if it's empty?
>
> du myfile.txt | grep '^0' && rm myfile.txt
>
> That seems easier than any other approach i can think of.
>

How about something like this, in your perl program:
-z $file && unlink $file;

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