linux多行折成一行

Question

linux下如何把多行文本按照规律换成一行呢？跪谢大佬

比如：

// a.txt  处理前
a
b
c

aaa
bbb
ccc

  ddd //每行前面可能会有多个空格
  fff
  gg
  gg
  gg




// 处理后，字符间使用空格间隔

a b c
aaa bbb ccc
ddd fff gg gg gg

Answer 1

The main idea is read the file line by line.
Print the line except white space if it has other characters.
You can get the characters using regex, then print it.
An example do it with perl:
cat a.txt | perl -ne 's/^\s*(\S+)\n$/\1 /g;print'
The regex will failed when the line only have white space.

Answer 2

试试这样：

sed ':a;N;$!ba;s/\n\n/--/g;s/\n/ /g;s/--/\n/g' a.txt