How to erase the file content

[kamesh3183]

Dear Monks
How to erase the content of a file without closing and opening it again
Update: I am using Win2k and ActiveState Perl 5.8.6.

Thanks
Kamesh

[jonadab]

How to erase the content of a file without closing and opening it again

As far as I am aware, every way to erase the contents of a file on NT involves, either directly or indirectly, opening it in overwrite mode, writing nothing, and closing. If you already had the file open, that will mean closing and opening again.

update: Unless you want to just delete the file. That will also have the side-effect of erasing its contents. If that's what you want, Perl's unlink command will do it for you.

[fishbot_v2]

From the question, it really sounds to me that the file is already open, and that the OP doesn't want to close it and re-open it. In which case, they are looking for truncate.

open my $fh, ">", "./foo.txt" 
   or die( "Couldn't etc." );
print $fh "$_\n" for 1..100;

truncate $fh, 0;

print $fh "$_\n" for 1..10;
close $fh;

Now foo.txt contains 1..10 only.

Update: As parv mentioned up-thread, this might close and re-open under the hood. It's not clear if you don't want to re-open for programatic reasons or for performance reasons.

[parv]

Assuming an Unix operating system...

I was going to say truncate but first i tried a kernel trace which indeed opens and closes the file. That leads me to say that redirecting stdin or /dev/null would do the same.

Only way seems to be rm -f file && touch file. Then again (seen via another kernel trace), touch also opened and closed the file.

Well, i am out of ideas...

[Anonymous Monk]

OP has mentioned Win2K. Then why you are assuming unix.

[sk]

The OP wanted to truncate a file without opening and closing the file.

I guess the OP updated the node and deleted the original contents. OP did not mention the OS before parv made the post

[sh1tn]

Just open in '>' mode:

{
 open my $fh, "> $file" or die "cannot open $file: $!"
}

[newroz]

perl -pi -e 's/.*//s' file

[gopalr]

Hi Kamesh,

Take a look at File::Slurp Module.

Thanks,
Gopal.R

[knsridhar]

try this

system(": > $filename");