in reply to Detect socket

You could try calling  getsockopt( $mysocket, getprotobyname( 'tcp' ), TCP_NODELAY ).

On my OS I get an error that tells me if the file descriptor provided is not a socket: 

getsockopt( STDOUT, getprotobyname( 'tcp' ), TCP_NODELAY ) 
    or warn "?$! :  $^E";;
?Unknown error :  An operation was attempted on something that is not 
+a socket

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