What is branch in sed

[Paul Howarth]

Dan Track wrote:
> On 8/23/06, Cameron Simpson <cs at zip.com.au> wrote:
>> On 23Aug2006 11:52, Dan Track <dan.track at gmail.com> wrote:
>> | I've searched and read documents on branching in sed (b) but I still
>> | can't get my head round it.
>> |
>> | Could someone please explain to me how branching works, an example
>> | would be nice.
>>
>> It's like goto. Here's an infinite loop:
>>
>>         :foo
>>         b foo
>>
>> Cheers,
>> -- 
> 
> Hi,
> 
> Thanks for the info. With that in mind I have the following example
> I'm having trouble unerstanding. Would you be able to help me out with
> understanding it? What does the $b in context to the whole file and
> executing the lines of code on the file. Also what does $!N mean? And
> do I really need P;D?
> 
> 
> sed -e '$b
> /^Target\[[^]]*\][.0-9]*:.*@[0-9.]*$/ {
> $!N
> s/^\(Target\[[^]]*\][.0-9]*:.*@\)[0-9.]*\nDirectory\[[^]]*\]:
> \(.*\)$/\1\2.example.com/
> P;D
> }' text_files/mrtg.cfg > text_files/mrtg.cfg.changed

The sed script quoted is heavily based on an example in the "sed FAQ" 
(http://sed.sourceforge.net/sedfaq4.html#s4.23.2); reading that document 
  is quite useful for people learning sed I think.

Paul.