Hi

Using GNU sed, how can I delete the line immediately _above_ the regexp?
Deleting the line below the regexp is no problem eg:

sed '/regexp/{n;d}' file

I cannot figure this one out.. but surely it's possible? I'm looking for a
"sed only" solution.

Thanks
Greg

Greg Schafer wrote:
>
> Hi
>
> Using GNU sed, how can I delete the line immediately _above_ the regexp?

Here is the awk way to do it...

$ awk 'NR>1 && !/pattern/ {print s} {s=$0} END {print s}'

> Deleting the line below the regexp is no problem eg:
>
> sed '/regexp/{n;d}' file
>
> I cannot figure this one out.. but surely it's possible? I'm looking for a
> "sed only" solution.

I am wondering why you prefer a cryptic sed solution to a clear and
extensible awk solution. I am no sed expert but this might do it...

$ sed -n '1h;1!{/pattern/h;/pattern/!{x};${x}}'

(There may be a way to avoid duplication of the pattern; I don't
bother.)

Janis

> Thanks
> Greg

Janis wrote:
> Greg Schafer wrote:
>> Hi
>>
>> Using GNU sed, how can I delete the line immediately _above_ the regexp?
>
> Here is the awk way to do it...
>
> $ awk 'NR>1 && !/pattern/ {print s} {s=$0} END {print s}'
>
>> Deleting the line below the regexp is no problem eg:
>>
>> sed '/regexp/{n;d}' file

Should be {n;d;} for standard sed and previous GNU sed.

>>
>> I cannot figure this one out.. but surely it's possible? I'm looking for a
>> "sed only" solution.
>
> I am wondering why you prefer a cryptic sed solution to a clear and
> extensible awk solution. I am no sed expert but this might do it...
>
> $ sed -n '1h;1!{/pattern/h;/pattern/!{x};${x}}'
>
> (There may be a way to avoid duplication of the pattern; I don't
> bother.)
>

Sure, there is.
But, compared to awk, a brain-teaser.

sed '1h;1d;/pattern/{h;$p;d;};x;$p;$x'

Standard sed is picky about the {} command groups;
they must be on separate lines or multiple -e args:

sed -e '1h;1d' -e '/pattern/{h;$p;d;}' -e 'x;$p;$x'

--
Michael Tosch @ hp : com