Shell Programming and Scripting

Hi all,
I have a large log file that gets created daily.

I need to be able to pull text out of the log when I hit a pattern including the 7 lines above it and the 3 lines below and output it to a new text file.

Line 1
Line 2
Line 3
Line 4
Line 5
Line 6
Line 7
Pattern
Line 9
Line 10
Line 11

I've tried using grep, awk and sed but am still a newbie and am having troubles.
Any help would be appreciated.

Well, you could do it in perl by building an array of 11 strings, and push in your lines until your array is full. Then check the 8th string for your pattern. If it doesn't match, pop the first one out, push a new one in, check again. When it does match, print out your array. It's a brute force method, but it should work.

You could do this same concept in awk or sed using buffers.

You might also try grep -p if you can identify a way to divide your lines into paragraphs. For example, if every log entry starts with a line of "++++++" and the text you're searching for is the 8th line of the log entry, do:
grep -p"++++++" "searchstring" logfile

That would be the easiest method.

Thanks for the reply Nick.

The extract I need does have a pattern of "========", but so do all the unwanted sections.

I didn't know I could put multiple lines into a buffer which may be of some help.

If I use the grep method, it will take almost the entire log as output unless I can specify it to only keep the section with the pattern I'm looking for.

That's exactly what the -p option does. Think of it as instead of searching line by line, search section by section, with the section divider being "=======", for whatever. Instead of just printing the one line where the pattern exists, it prints the one section.

If you're having problems getting the sections to break up correctly, try using fgrep -p. You might need to include an entire line of the "=" as the argument to -p to get it to work. I have a log file where the divider is a line of * characters, and I remember having to play around with it for a while until I found the combination that worked.

man your grep and see if there's a -A or -B option.

An awk solution:

Code:

awk '
BEGIN {i=1}
{
vec[i]=$0
i++
if ( $0 ~ /Pattern/ ) {
          for (j=i-8;j<i;j++)
             print vec[j]
          for (j=1;j<=3;j++)
             {
             getline
             print
             }
          i=1
          }
}' file

Hi,
My grep has a -b option. No -A -B or -p option exists.

I also used the awk code and it was the closest thing that's worked.... but the output shows.

data
data
data
data
----------------------------------
data
data
data
data
data
data
data
pattern
data
data
data
----------------------------------
data
data
data
data
data
data

That's really close to what I'm looking for.