You don't say what you think the problem is, but I'm guessing that you are expecting either $_ or the contents of @trt_files to be updated by what you are doing. Perhaps you need a closer look at what is going on.

foreach (@trt_files) # Each time round the loop, $_
                     # is set to an alias to one of the
                     # elements of @trt_files.
{
    $record = $_;    # $record now contains the _value_
                     # of $_. It is _not_ an alias into
                     # @trt_files.
    $record =~ s/date/$date/; # This changes $record
                              # (it doesn't change $_
                              # or @trt_files).
    print "$_\n";    # Prints the (unchanged) value of $_
}
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If I'm right, then what you actually want is far simpler than what you have.

foreach (@trt_files)
{
    s/date/$date/;
    print "$_\n";
}
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