You could take a look at File::Slurp's edit_file sub. This allows you to edit file contents. You could push the contents from $_ to another variable and then clear $_. I'm not sure how locks are done internally though.

use File::Slurp qw(edit_file);

my $contents = '';
edit_file { $contents = $_; $_ = '';} 'temp/test.txt';
print $contents;
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