1> perl -e 'use IO::Handle; open(FH,">out"); FH->autoflush(1); if(fork){ print FH "aaaa"; sleep 2; print FH "bbb"; close FH }else{ sleep 1; print FH "1111"; seek FH,0,0; print FH "4"; close FH }' #### 2> perl -e 'use IO::Handle; open(FH,">out"); FH->autoflush(1); if(fork){ print FH "aaaa"; sleep 2; print FH "bbb"; close FH }else{ close FH;open(FH,"+autoflush(1); sleep 1; print FH "1111"; seek FH,0,0; print FH "4"; close FH1 }'