sed - 使用 sed 加入某些行

Question

我有一个看起来像这样的输入:

1
2

3
4
5

6

我想用 sed 将它转换为:

12
345
6

我知道可以使用其他工具轻松完成，但我想专门使用 sed 作为学习练习来完成。我试过这个:

sed ':x ; /^ *$/{ N; s/\n// ; bx; }'

但它打印:

123456

有人可以帮我解决这个问题吗？

Answer 1

引自GNU sed manual :

A common technique to process blocks of text such as paragraphs (instead of line-by-line) is using the following construct:

sed '/./{H;$!d} ; x ; s/REGEXP/REPLACEMENT/'

1. The first expression, /./{H;$!d} operates on all non-empty lines, and adds the current line (in the pattern space) to the hold space. On all lines except the last, the pattern space is deleted and the cycle is restarted.

2. The other expressions x and s are executed only on empty lines (i.e. paragraph separators). The x command fetches the accumulated lines from the hold space back to the pattern space. The s/// command then operates on all the text in the paragraph (including the embedded newlines).

确实，

sed '/./{H;$!d} ; x ; s/\n//g'

做你想做的。