Re: How to search a match on a line and then make a change on the next line?

On Thu, May 14, 2020 at 12:52:29PM -0500, Tim Chase wrote:
>On 2020-05-14 12:27, boB Stepp wrote:
>> On Thu, May 14, 2020 at 08:00:38AM -0500, Tim Chase wrote:
>> > :%s/\(\<field \+\w*\)address2.*\n\s*\zs\zepobox\>/\1
>>
>> Thank you, this works. I had to look up some of the flags you used
>> before I understood what you are doing. In my particular example I
>> found I did not need to use "\+", "\<" and "\>" to get the desired
>> result. But I suspect that you are using these to protect against
>> scenarios I am not considering. Would you mind elaborating on why
>> you included those additional flags?
>
>The space followed by \+ requires at least one but possibly more than
>one space between "field" and the start of the field-name. So it
>takes into consideration
>
> field work_address2 STANDARD FIELD -- note multiple spaces
>
>The \< prevents strange situations like
>
> greenfield work_address
>
>by ensuring that "field" stands alone without junk at the beginning.
>Unlikely, but handy to specify up front. Likewise the \> prevents
>it from finding something like "pobox2". Which you might or might
>not want. Adjust according to your requirements.

Ah! All of that makes sense now and it is something that I should be
practicing. Thank you!

>> As I am trying to understand the "why"s of all of this, it would be
>> helpful for my understanding if someone would explain why my regex
>> did not work as expected. I am still not seeing it.
>> :g/\(field [[:alnum:]_]*\)address2/+s/pobox/\1pobox/
>
>As best I understand, the items captured in the g// portion don't
>carry over for reuse in the s// replacement (the s// resets the
>capture groups). Otherwsie, I believe it would work since
>
> :g/\(field [[:alnum:]_]*\)address2/+
>
>correctly finds the first lines and
>
> s/pobox/XYZ/
>
>correctly does a substitution, merely lacking access to the captured
>\1 group. If you add some brackets around the \1 you'll see the
>effect:
>
> :g/\(field [[:alnum:]_]*\)address2/+s/pobox/[\1]pobox/
>
>you'll see resulting lines like
>
> []pobox
>
>to show that the contents of \1 are empty.

Hmm. That is what I was speculating -- that "\1" was empty -- and you have
proven that plus giving me another little trouble shooting technique. But
an example in the book "Learning the vi and Vim Editors, 7th ed." by Arnold
Robbins, Elbert Hannah and Linda Lamb made me believe what I was trying was
doable. In chapter 6: Global Replacement on page 82 the authors give this
snippet of text:

mgibox routine;
mgrbox routine;
mgabox routine;

In this exercise we want to replace "box" with "square". The authors give
two ways to accomplish this. One of them is:

:g/mg\([ira]]\)box/s//mg\1square/g

Here where the line found is also the line to change (unlike mine where I
want to change the next line) the "\1" register is accessible. I tried my
case with "g" on the end, but it did not make any difference. Obviously
there is still something here I am not comprehending properly.

--
Wishing you only the best,

boB Stepp

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