my @strings = (
  'test[abc]test',
  'test[cde]test',
  'test[ack]test',
);

my $regex = qr/
  \b\[         # Require a word boundary and match an open bracket.
  (\w+)        # Capture one or more "word" characters.
  \]\b         # Match a close bracket and require a word boundary.
/x;

foreach my $string ( @strings ) {
  if( my( $name ) = $string =~ $regex ) {
    print "$name\n";
  }
}