glob is a list generator. An entry will be generated for each value of a list in curlies 
$ perl -le'print for glob "{a,b,c}{d,e,f}"'
ad
ae
af
bd
be
bf
cd
ce
cf

[download]

A shell example: 

cp file{,.bk}

[download]
is the same as 
cp file file.bk

[download]

In reply to Re^3: Multiplexing array of arrays? by ikegami
in thread Multiplexing array of arrays? by mpettis

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