It's likely that snippet should be:

while(chomp(my $line = <$fh>)) {
    $show .= "$line\n";
}
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And that is pretty much functionally equivalent to:

{
    local $/ = undef;
    $show = <$fh>;
}
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...except that his code would append a newline at the end of the file if one wasn't there already. So $show =~ s/(?<!\n)\z/\n/ if that trailing newline is important. If he intended to keep the lines separated then he could slurp into an array.