#删除当前文本里的空行，查看结果可知第17和19行的空行被删除了。sed '/^$/ d' emp.txt

7369,smith,clerk,7902,'1980-12-17',800,null,207499,allen,salesman,7698,'1981-2-20',1600,300,307521,ward,salesman,7698,'1981-2-22',1250,500,307566,jones,manager,7839,'1981-4-2',2975,null,207654,martin,salesman,7698,'1981-9-28',1250,1400,307655,jack,manager,7698,'1987-3-28',1600,1800,107656,tim,clerk,7902,'1982-12-12',1400,1400,307657,kate,clerk,7902,'1989-11-11',1400,1800,107698,blake,manager,7839,'1981-5-1',2850,null,307699,dlake,salesman,7839,'1983-6-15',3000,null,107782,clark,manager,7839,'1981-1-9',2450,null,107788,scott,analyst,7566,'1982-12-9,3000,null,207839,king,president,null,'1981-11-17',5000,null,107844,turner,salesman,7698,'1981-12-8',1500,0,307876,adams,clerk,7788,'1983-1-12',1100,null,207900,james,clerk,7698,'1981-12-3',950,null,30--7902,ford,analyst,7566,'1981-12-3',3000,null,207934,miller,clerk,7782,'1982-1-23',1300,null,10