Update: (added a little more code)

You might consider:

use strict;
my $file = '/tmp/this_file';
my $fh;
unless (open($fh,">$file")) {
  die "I can't open $file for writing: $!";
}
truncate $fh, 0;
close($fh);
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Of course, this example is a little contrived, since if you open the file for writing like that and then close it, I think it will truncate it without needing the truncate command. But I can conceive of using that truncate() command if I had been writing to a file and then decided to start over. I must admit, I have never used it.

Another update: Ah, as pointed out by [id://bluto], the truncate command also can be called in the form:

  truncate $myfile, 0;
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... which is at least somewhat more useful.

If the file is not owned by you, then you may need to have group- or world- writable permissions set on it, depending on your operating system.