Thanks to all who responded. The answered ended up being that flock requires an open filehandle. Windows won't allow a filehandle to be opened if the file hasn't been fully written. (Something about copying to a temp file and renaming.)

The following script will work.

(Update: Removed the flock check because it isn't needed and will hang on the Samba share I'm testing with.)

#!/usr/bin/perl
 
use strict;
use warnings;
 
use IO::File;
 
my ($fn) = @ARGV;
 
die "Must pass a filename\n" unless defined $fn && length $fn;
 
my %checks = (
        exist => 10,
        age   => 3,
        fopen => 20,
);
 
my $std_wait = 2;
my %wait = (
        exist => $std_wait,
        age   => $std_wait,
        fopen => $std_wait,
);
 
my $file_exists = -e $fn;
my $exist_checks = $checks{exist};
 
while (!$file_exists || --$exist_checks)
{
        sleep $wait{exist};
 
        $file_exists = -e $fn;
        last if $file_exists;
}
 
unless ($exist_checks)
{
        die "File '$fn' doesn't exist in $checks{exist} checks\n";
}
 
my $old_mod = (stat $fn)[9];
my $num_checks = $checks{age};
while ($num_checks)
{
        sleep $wait{age};
 
        my $current_mod = (stat $fn)[9];
        if ($old_mod == $current_mod)
        {
                $num_checks--;
                next;
        }
 
        $num_checks = $checks{age};
        $old_mod = $current_mod;
}
 
my $fh;
my $fopen_checks = $checks{fopen};
while (--$fopen_checks)
{
        $fh = IO::File->new(">>$fn") and last;
        sleep $wait{fopen};
}
 
unless ($fopen_checks)
{
        die "Could not open '$fn' for reading in $checks{fopen} checks
+\n";
}
 
$fh->close;
 
print "File has fully arrived!\n";
[download]

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