下面是我在Vim中的做法：

:g/when/normal mzvip^[:'zt'>^M

其中^[是用<C-v><Esc>获得的，^M是用<C-v><CR>获得的。
明细：

• :g/<pattern>/<command>在与<pattern>匹配的每一行上执行<command>。
• :normal xxx从命令行模式执行常规命令。
• mz将标记'z放置在匹配行上。
• vip可视地选择当前段落，并在其最后一行放置标记'>。
• <Esc>退出可视模式。
• :'zt'>将带有标记'z行复制到带有标记'>行下面
• <CR>执行最后一个命令。

请参阅:help :global、:help :normal、:help mark-motions、:h :t和:h :range。
请注意，直观地使用标记'}，如下所示：

:g/when/t'}

看起来它可以很好地解决这个问题，但是Vim在实际段落后的第一个空行上做了标记'}，这对我们没有帮助，因为我们的锚是实际段落的最后一行。
这就是为什么vip舞蹈是必要的原因之一：我们需要在段落的最后一行上，而不是在之后添加一个标记，并且可视地选择“内部段落”就可以使用标记'>来实现这一点。

使用awk可以执行以下操作：

awk -F ': ' '
$1 ~ / when$/ {var = $0}
NR > 1 {print prev}
!NF && prev ~ /^- task/ {print var}
{prev = $0}
END {
   print prev
   if (prev ~ /^- task/)
      print var
}' file

输出：

- set_fact: something
- set_fact: somethingelse
- task: do the foo
  when: var_a
- task: do the goo
  when: var_a

- set_fact: something
- set_fact: somethingelse
- task: do the fofo
  when: var_b
- task: do the gogp
  when: var_b

- set_fact: something
- set_fact: somethingelse
- task: do the fooolo
  when: var_c
- task: do the gooolo
  when: var_c

在vim中，你可以这样做：

• qq开始录制名为q的宏
• /when: Enter查找下一个出现的when:
• yy猛拉当前行
• j向下移动光标
• p在下面粘贴线条
• q终止宏录制

此时，您可以根据需要键入@q来多次调用宏。
你也可以提前知道你需要执行多少次这样的操作，用:%s/when://ng来查找when:的出现次数，这将打印出类似3 matches on 3 lines的内容。然后你可以只键入例如3@q来调用宏3次。

If ed is available/acceptable.

printf '%s\n' 'g/^[[:space:]]\{1,\}when: var_.*/t.1' ,p Q | ed -s file.yaml

If the output is correct, and in-place editing is needed, change

,p Q

to

w q

I only have GNU ed at hand.

• g

Globally substitute for all non-overlapping instances of the RE rather than just the first one. If both g and count are specified, the results are unspecified.

• (1,$) g /RE/command list
• (.,.) t address

The t command shall be equivalent to the m command, except that a copy of the addressed lines shall be placed after address address (which can be 0); the current line number shall be set to the address of the last line added.

• .

The period character ( . ) shall address the current line.

• The positive decimal number n shall address the nth line of the edit buffer.
• , or %

Depending on the variant shall address the whole buffer. ,p or %p

• (.,.) p

The p command shall write to standard output the addressed lines; the current line number shall be set to the address of the last line written. The p command can be appended to any command other than e, E, f, q, Q, r, w, or !.

• w The w command shall write the addressed lines into the file named by the pathname file.
• q

The q command shall cause ed to exit. If the buffer has changed since the last time the entire buffer was written, the user shall be warned, as described previously.

• Q

The Q command shall cause ed to exit without checking whether changes have been made in the buffer since the last w command.

• -s Suppress the writing of byte counts by e, E, r, and w commands and of the '!' prompt after a !command.

See

• POSIX ed
• GNU ed

In vim something like.

:g/^[[:space:]]*when: var_.*/t.1

要从输入中得到输出，您需要使用任何awk：

$ awk -v RS= -F'\n' '{print $0 ORS $(NF-1) ORS}' file
- set_fact: something
- set_fact: var_a
- task: do the foo
  when: var_a
- task: do the goo
  when: var_a

- set_fact: something
- set_fact: var_b
- task: do the fofo
  when: var_b
- task: do the gogp
  when: var_b

- set_fact: something
- set_fact: var_c
- task: do the fooolo
  when: var_c
- task: do the gooolo
  when: var_c

或者如果实际输入比前面显示的更复杂，也可以使用任何awk：

$ awk '/when:/{w=$0} {print} /task:/ && w{print w; w=""}' file
- set_fact: something
- set_fact: var_a
- task: do the foo
  when: var_a
- task: do the goo
  when: var_a

- set_fact: something
- set_fact: var_b
- task: do the fofo
  when: var_b
- task: do the gogp
  when: var_b

- set_fact: something
- set_fact: var_c
- task: do the fooolo
  when: var_c
- task: do the gooolo
  when: var_c

第一个