Hi Swift,
You should take a look at perldoc -f open.

If you don't want to open twice, once for writing and again for reading, use "+<" as the mode for the initial open like so:

my $file = "D:/swift/file.tmp";
open (FILE, "+< $file") || die "Couldn't open $file: $!";
print FILE "Add some text";
close (FILE);
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By the way, you don't need to double up backslashes; you can use single forward slashes as path delimiters on Windows. Just one less thing to worry about. And checking to see if open calls were successful is a good idea.

Hope this helps.