Its in the manual , See File::Glob for details.

The metanotation a{b,c,d}e is a shorthand for abe ace ade . Left to right order is preserved, with results of matches being sorted separately at a low level to preserve this order. As a special case {, }, and {} are passed undisturbed.

$ perl -le"print for glob shift" "abe ace ade"
abe
ace
ade

$ perl -le"print for glob shift" "see also sea shore "
see
also
sea
shore

$
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