Bash:用字符串替换空行

Question

如何替换文本文件中的空行,假设该文件是:

first

third

用一些字符串(例如"第二")使用Bash？我想做某事 像这样:

first
second
third

Answer 1

你可以使用sed:

sed -i -e 's/^$/second/' file

该-i选项可切换就地替换.

Answer 2

您还可以对未设置或空变量使用默认值:

cat file.txt | while read line
do
   echo "${line:-second}"  # empty lines are default to 'second'
done > file.out