system ("tremove @host:$ep");

That solves one problem by creating another. You've solved the problem of $ep not interpolating, but you've created the problem of @host interpolating, when the OP stated it's not intended to be a variable.

You could use either of the following techniques:

system( 'tremove @host:' . $ep );
system( "tremove \@host:$ep" );
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