On 8/23/06, Paul Howarth <paul@xxxxxxxxxxxx> wrote:
Dan Track wrote:
> On 8/23/06, Cameron Simpson <cs@xxxxxxxxxx> wrote:
>> On 23Aug2006 11:52, Dan Track <dan.track@xxxxxxxxx> 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\[[^]]*\]:
> \(.*\)$/\1\2.example.com/
> P;D
> }' text_files/mrtg.cfg > text_files/mrtg.cfg.changed
The sed script quoted is heavily based on an example in the "sed FAQ"
(http://sed.sourceforge.net/sedfaq4.html#s4.23.2); reading that document
is quite useful for people learning sed I think.
Paul.
Hi Paul,
Thanks for the info. As a small query I'm kind of understanding what b
means, but what does "$b" mean and how does it affect the script. I
thought what preceded b was the matching clause which dictates when a
jump should be performed. So how does the "$" come into play?
Thanks
Dan
