$ perl -Mbignum=a,50 -wle'print hex("0xbe91cfb586466d02")'
Integer overflow in hexadecimal number at -e line 1.
Hexadecimal number > 0xffffffff non-portable at -e line 1.
1.37319851173781e+19

##</code><code>##

$ perl -MMath::BigInt -wle'print hex(Math::BigInt->new("0xbe91cfb586466d02"))'
Integer overflow in hexadecimal number at -e line 1.
Hexadecimal number > 0xffffffff non-portable at -e line 1.
9.18481776382103e+22

##</code><code>##

$ perl -Mbigint -wle'print 0+"0xbe91cfb586466d02"'
13731985117378145538

##</code><code>##

$ perl -MMath::BigInt -wle'print Math::BigInt->new(0)+"0xbe91cfb586466d02"'
13731985117378145538

##</code><code>##

$ perl -MMath::BigInt -wle'print Math::BigInt->new(0)->badd(Math::BigInt->new("0xbe91cfb586466d02"))'
13731985117378145538

##</code><code>##

$ perl -MMath::BigInt -wle'print Math::BigInt->new("0xbe91cfb586466d02")'
13731985117378145538