Allocating and deallocating repeatedly the 1024-byte buffer for stdout from
builtins costs CPU time for little or no benefit.
A simple loop containing builtins that write to a file descriptor, such as
i=0; while [ "$i" -lt 1000000 ]; do printf .; i=$((i+1)); done >/dev/null
is over 10% faster in a simple benchmark on an amd64 virtual machine.
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