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&{
    bg exe sub { "2>#" }, qw( ls  /tmp  does_not_exist ),
...
       exe qw(cat -n),
       exe sub { print "six> $_" while <STDIN>; print "5th cmd: @_\n" 
+},
};

{ ls /tmp does_not_exist 2> /dev/null | tac | [perlsub] | { sort | cat
+ -n | [perlsub] } & } &

exe &PREEXEC, LIST, &READER
exe &PREEXEC, &READER
exe &READER

      "2>null"    # silence  stderr
      ">#"        # silence  stdout
      "2>&1"      # redirect stderr to  stdout
      "1>&2"      # redirect stdout to  stderr
      "1><2"      # swap     stdout and stderr

bg &BACKGROUND

package IPC::Exe;

...
}

'IPC::Exe';