C:\test>perl -MAlgorithm::Combinatorics=variations -E"$i=variations( ['A'..'D'], 3 ); say @$_ while $_= $i->next"
ABC
ABD
ACB
ACD
ADB
ADC
BAC
BAD
BCA
BCD
BDA
BDC
CAB
CAD
CBA
CBD
CDA
CDB
DAB
DAC
DBA
DBC
DCA
DCB