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sub trim {
    @_ = @_ ? @_ : $_ if defined wantarray;
...
    # defined values, if any. Otherwise just return.

}

@trimmed = trim(@not_trimmed);

foreach (@untrimmed) {
   say trim;
}

sub trim (_;@) { 
   # ... as above
...
my @data = (' a', ' b ' , 'c ');

say trim (@data);