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From: Janis Papanagnou on 6 Oct 2009 20:42
Grant wrote:
> On Wed, 07 Oct 2009 01:50:16 +0200, Janis Papanagnou <janis_papanagnou(a)hotmail.com> wrote:
>
>> Jack Shown wrote:
>>> Is it possible using sed, awk, perl or anything else to search a file
>>> for a regex and if that line is followed by another regex then display
>>> both lines otherwise display only the first line?
>> awk '
>> /pattern1/ {print; flag=1; next}
>> /pattern2/ && flag {print}
>> {flag=0}
>> '
>
> Is it faster if you swapped /pattern2/ and flag?

Probably; if you are processing many millions of lines. :-)

> (does (g)awk do short circuit logic?)

Yes.

Janis

>
> Grant.
From: Ed Morton on 6 Oct 2009 23:27
sharma__r(a)hotmail.com wrote:
> On Oct 7, 4:17 am, Jack Shown <jacksh...(a)gmail.com> wrote:
>> Is it possible using sed, awk, perl or anything else to search a file
>> for a regex and if that line is followed by another regex then display
>> both lines otherwise display only the first line?
>>
>> For example, suppose I grep a file for "Ultra" but want the following
>> line also output if the following line contains "fixed".
>>
>> Thanks.
>
> One way to do it is (using "sed"):
>
> sed -e '
> /Ultra/\!d
> n
> /fixed/\!d
> ' yourfile

Hmm, that fails for me:

$ sed -e '
/Ultra/\!d
n
/fixed/\!d
' file
sed: -e expression #1, char 12: unknown command: `\'

$ sed --version
GNU sed version 4.1.5

What Janis suggested seems to work, though:

$ awk '/Ultra/ {print; found=1; next}
found && /fixed/ {print}
{found=0}' file

Regards,

Ed.
From: Jack Shown on 6 Oct 2009 23:48
On Oct 6, 4:50 pm, Janis Papanagnou <janis_papanag...(a)hotmail.com>
wrote:
> Jack Shown wrote:
> > Is it possible using sed, awk, perl or anything else to search a file
> > for a regex and if that line is followed by another regex then display
> > both lines otherwise display only the first line?
>
>    awk '
>      /pattern1/ {print; flag=1; next}
>      /pattern2/ && flag {print}
>      {flag=0}
>    '
>
> Janis
>
>
>
>
>
> > For example, suppose I grep a file for "Ultra" but want the following
> > line also output if the following line contains "fixed".
>
> > Thanks.

Works perfectly! Thanks, Janis and everyone else.
From: pk on 7 Oct 2009 04:31
Ed Morton wrote:

>> One way to do it is (using "sed"):
>>
>> sed -e '
>> /Ultra/\!d
>> n
>> /fixed/\!d
>> ' yourfile
>
> Hmm, that fails for me:
>
> $ sed -e '
> /Ultra/\!d
> n
> /fixed/\!d
> ' file
> sed: -e expression #1, char 12: unknown command: `\'

Yeah you don't need the backslash before the "!" (or use awk as you already
said).


From: sharma__r on 7 Oct 2009 11:47
On Oct 7, 8:27 am, Ed Morton <mortons...(a)gmail.com> wrote:
> sharma...(a)hotmail.com wrote:
> > On Oct 7, 4:17 am, Jack Shown <jacksh...(a)gmail.com> wrote:
> >> Is it possible using sed, awk, perl or anything else to search a file
> >> for a regex and if that line is followed by another regex then display
> >> both lines otherwise display only the first line?
>
> >> For example, suppose I grep a file for "Ultra" but want the following
> >> line also output if the following line contains "fixed".
>
> >> Thanks.
>
> > One way to do it is (using "sed"):
>
> > sed -e '
> >    /Ultra/\!d
> >    n
> >    /fixed/\!d
> > ' yourfile
>
> Hmm, that fails for me:
>
> $ sed -e '
>     /Ultra/\!d
>     n
>     /fixed/\!d
> ' file
> sed: -e expression #1, char 12: unknown command: `\'
>
> $ sed --version
> GNU sed version 4.1.5
>


This will work:

sed -e '
/pattern1/!d
n
/pattern2/!d
' yourfile


-- Rakesh
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