linux/shell 文本文件删除/删掉空行

1 sed '/^$/d' input.txt > output.txt    #output file: output.txt
2 sed -i '/^$/d' input.txt      #output file: input.txt
3 awk 'NF > 0' input.txt > output.txt     #output file: output.txt
4 perl -i.backup -n -e "print if /\S/" input.txt   #output file: input.txt.backup
5 grep -v '^$' input.txt > output.txt    #output file: output.txt