下面你看到了我的真实的代码，我想它可以简化为

$ echo 123456789012 | awk '{print $1}'
123456789012

问题

如何让awk添加冒号，它会输出12:34:56:78:90:12？

grep -v '^#' $hosts | grep -E '[0-9A-F]{12}\b' | grep -v 000000000000 | awk '{
    print "host "$5" {"
    print "  option host-name \""$5"\";"
    print "  hardware ethernet "$3";"
    print "  fixed-address "$1";"
    print "}"
    print ""
}' > /etc/dhcp/reservations.conf