CentOS - Aug 2007 - grep

Not a CentOS specific question, although I am running grep on CentOS 4.3
but how would you grep out a series of lines in a file starting at a
specific point.  For instance, if I have a file named foo and I want to
grep out the next 5 lines after the first and only instance of the
string "bar" how could I pull that off?  Thanks so much.

> Not a CentOS specific question, although I am running grep on CentOS 4.3
> but how would you grep out a series of lines in a file starting at a
> specific point.  For instance, if I have a file named foo and I want to
> grep out the next 5 lines after the first and only instance of the
> string "bar" how could I pull that off?  Thanks so much.
What do you mean by "grep out" ?  Do you want to display those lines,
or skip those lines?  Do you want to see the "bar" line?  Is that
included
in the 5 lines?

Anyway, you probably want to use "sed" here, rather than
"grep".

-- 

rgds
Stephen

On 8/28/07, Scott McClanahan <scott.mcclanahan at trnswrks.com>
wrote:
> Not a CentOS specific question, although I am running grep on CentOS 4.3
> but how would you grep out a series of lines in a file starting at a
> specific point.  For instance, if I have a file named foo and I want to
> grep out the next 5 lines after the first and only instance of the
> string "bar" how could I pull that off?  Thanks so much.

'grep -A 5 bar foo' should do the trick.  From the grep manpage ->
-A NUM, --after-context=NUM
              Print NUM lines of trailing context after matching
lines.  Places a line containing -- between contiguous groups of
matches.



-- 
During times of universal deceit, telling the truth becomes a revolutionary act.
George Orwell

On Aug 28, 2007, at 10:05 AM, Scott McClanahan wrote:
> Not a CentOS specific question, although I am running grep on  
> CentOS 4.3
> but how would you grep out a series of lines in a file starting at a
> specific point.  For instance, if I have a file named foo and I  
> want to
> grep out the next 5 lines after the first and only instance of the
> string "bar" how could I pull that off?  Thanks so much.
for the line matching "bar" and the next five lines after it:

$ grep -A 5 bar foo

if you don't want the line matching "bar":

$ grep -A 5 bar foo | tail -5

-steve

--
If this were played upon a stage now, I could condemn it as an  
improbable fiction. - Fabian, Twelfth Night, III,v

> 
> Not a CentOS specific question, although I am running grep on 
> CentOS 4.3
> but how would you grep out a series of lines in a file starting at a
> specific point.  For instance, if I have a file named foo and 
> I want to
> grep out the next 5 lines after the first and only instance of the
> string "bar" how could I pull that off?  Thanks so much.
> 
"man grep" is your friend here

Quoting (cause they explain it better than I):
OPTIONS
       -A NUM, --after-context=NUM
              Print NUM  lines  of  trailing  context  after  matching
lines.
              Places  a  line  containing  --  between  contiguous
groups  of
              matches.

.
.
.
.
       -m NUM, --max-count=NUM
              Stop reading a file after NUM matching lines.  If the
input  is
              standard  input  from a regular file, and NUM matching
lines are
              output, grep ensures that the standard input  is
positioned  to
              just  after the last matching line before exiting,
regardless of
              the presence of trailing context lines.  This enables a
calling
              process  to resume a search.  When grep stops after NUM
matching
              lines, it outputs any trailing context lines.  When  the
-c  or
              --count  option  is  also  used,  grep  does  not output a
count
              greater than NUM.  When the -v or --invert-match option is
also
              used, grep stops after outputting NUM non-matching lines.



So your command would look something like this:

grep -m1 -A5 bar foo


This does not handle your case of "first and only" instance however.
It
will stop after the first instance of the word bar.

Scott McClanahan wrote:
> grep out the next 5 lines after the first and only instance 
The scope of grep's view of the world is a single line.  At any one 
time, it knows nothing more.

If you need to deal with multiple lines, I suggest perl.  Untested code:

#!/usr/bin/perl
while (<>) {
	if (m/bar/) {
		for ($i = 0; $i < 5 and defined($_); ++$i) {
			print;
			$_ = <>;
		}
		last;
	}
}

Rodrigo Barbosa wrote:
> 
> Ick. I hate perl.
> 
> If I find something I can't do in bash/sed/awk, I just code it in C :)
Ick.  I hate C.  ;)

If I can't use grep, I'll use an short inline Perl script.  Or, in
extreme cases, I'll write a small utility script.  Or, more commonly,
I'll write a huge inline Perl monstrosity that really should have been
done as a utility script.  (It's really hard to sort out nested loops
and conditionals without any formatting...)

-- 
Bowie

On Tue, 2007-08-28 at 10:05 -0400, Scott McClanahan
wrote:
> Not a CentOS specific question, although I am running grep on CentOS 4.3
> but how would you grep out a series of lines in a file starting at a
> specific point.  For instance, if I have a file named foo and I want to
> grep out the next 5 lines after the first and only instance of the
> string "bar" how could I pull that off?  Thanks so much.
I know I'm late on this and there have been many fine replies. I prefer
csplit for tasks like this. As always with *IX, many ways to skin the
cat.
> <snip>
--
Bill