It is not clear whether "[t4 w4]" is an array reference, or plain text. Assuming the latter :

my @a=(qw(w1 w2 w3),"[t4 w4]" ,qw(w5 w6)); 
  m/\[(\S+)\s(\S+)\]/ ? print qq[$2 $1\n] :print qq[$_\n] for @a
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FYI - it is pointless using "map" in a void context - "for" is preferable.

If you have an array ref, the code is:

my @a=(qw(w1 w2 w3),["t4","w4"],qw(w5 w6));

ref $_ ? print "$_->[1] $_->[0]\n" :print qq[$_\n] for @a
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Of course, for production-level code, you would do a lot more error-checking.