From type/Allomorph

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method trim(Allomorph:D:)

Calls Str.trim on the invocant's Str value.

From type/Cool

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sub trim(Str(Cool))
method trim()

Coerces the invocant (or in sub form, its argument) to Str, and returns the string with both leading and trailing whitespace stripped.

my $stripped = '  abc '.trim;
say "<$stripped>";          # OUTPUT: «<abc>␤»

From type/Str

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method trim(Str:D: --> Str)

Remove leading and trailing whitespace. It can be used both as a method on strings and as a function. When used as a method it will return the trimmed string. In order to do in-place trimming, one needs to write .=trim

my $line = '   hello world    ';
say '<' ~ $line.trim ~ '>';        # OUTPUT: «<hello world>␤» 
say '<' ~ trim($line) ~ '>';       # OUTPUT: «<hello world>␤» 
$line.trim;
say '<' ~ $line ~ '>';             # OUTPUT: «<   hello world    >␤» 
$line.=trim;
say '<' ~ $line ~ '>';             # OUTPUT: «<hello world>␤»

See also trim-trailing and trim-leading.