Usually, Perl is right with its error message. You're not giving the filename to open and hence Perl complains that it doesn't know what to do:

open(LOGFILE)
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You need to give open the filename to open, and I recommend using lexical filehandles if your version of Perl supports them (since 5.6.0):

open my $fh, "<", $LOGFILE
    or die "Couldn't open '$LOGFILE': $!";
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