use File::Temp qw( );

my $tmpdir = File::Temp->newdir( CLEANUP => 0 );

...

$tmpdir->unlink_on_destroy( 1 ) if $success;
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Test:

$ tt() {
   perl -e'
      use v5.14;
      use File::Temp qw( );
      my $tmpdir = File::Temp->newdir( CLEANUP => 0 );
      say $tmpdir;
      my $success = $ARGV[0];
      $tmpdir->unlink_on_destroy( 1 ) if $success;
   ' -- "$@"
}

$ t() {
   local tmpdir=$( tt "$@" )
   if [ -e "$tmpdir" ]; then
      echo Preserved
      rm -r -- "$tmpdir"
   else
      echo Cleaned
   fi
}

$ t 0
Preserved

$ t 1
Cleaned
[download]

Update: Needed to switch from File::Temp::tempdir to File::Temp->newdir to work.