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my $uri;
foreach ( 
...
) {
   $uri.="$_/" if ( defined $_ && length($_) ) #omit undef and empties
}

my @part = ( 
   'http://example.net/app', 
...
foreach (@parts) { 
   $uri.="$_/" if ( defined $_ && length($_) ) #omit undef and empties
}