PS D:\tmp> perl -E"$|=1;print $]" >.\tmp.log                    # writes log immediately 
PS D:\tmp> cat .\tmp.log
5.032001
PS D:\tmp> perl -E"$|=1;print $];sleep 100" >.\tmp.log          # doesn't write log 
Terminating on signal SIGINT(2)
PS D:\tmp> cat .\tmp.log                                        # empty
PS D:\tmp> exit

d:\tmp>perl -E"$|=1;print $];sleep 100" >.\tmp.log              # writes log immediately
Terminating on signal SIGINT(2)

d:\tmp> type .\tmp.log
5.032001