Ok here is how I got it to work. I used a signal handler to close and reopen the file. 
while (1) {
    $SIG{USR1} = sub {
    close $file;
    my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localti
+me(time);
    my $hrmin = sprintf ("%02d%02d",$hour,$min);
    my $ymd = sprintf("%04d%02d%02d%02d%02d%02d",$year+1900,$mon+1,$md
+ay,$hour,$min,$sec);
    my $filename = "/tmp/$ymd.txt";
    print $filename, "\n";
    open $file, ">$filename" || die("Couldn't open $file");
    };
  while (my $line = <$sock>) {

    if ($line =~ m/^(ALARM: )/) {

[download]
Now I can just use the log rotate system to send a killall -USR1 to start a new file.

In reply to Re^3: Close a file and reopen a new one at midnight by Anonymous Monk
in thread Close a file and reopen a new one at midnight by Anonymous Monk

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