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Full Discussion: How to grep and print the next and previous N lines after the hit
Top Forums Shell Programming and Scripting How to grep and print the next and previous N lines after the hit Post 302910128 by Corona688 on Tuesday 22nd of July 2014 02:43:42 PM
Old 07-22-2014
Code:
$ cat context.awk

BEGIN {
        BEFORE=5;
        AFTER=5;
        MAX=10
        C=-1;
}

function last(N)
{
        if(N>L) return("");
        return(LINE[(L-N)%MAX]);
}

(BEFORE >= MAX) { MAX=BEFORE+1 }

{ LINE[(++L)%MAX]=$0 } # Remember line for later


(C--) > 0  {
        if($0 ~ PAT)    C=AFTER;
        print ; next
}

($0 ~ PAT) {
        # Extra checking to avoid re-printing lines from 'after'
        C += AFTER-1;
        if((C < 0) && ((-C) <= AFTER))  C=-C;
        else    C=BEFORE;

        for(N=C; N>=0; N--) print last(N);
        C=AFTER;
}

$ cat input

c
d
e
f
pat
g
h
h
i
i
pat
j
k
l
m
n
o
p

$ awk -f context.awk PAT="pat" BEFORE=3 AFTER=2 input

d
e
f
pat
g
h
h
i
i
pat
j
k

$

 

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LEARN ABOUT PLAN9

zgrep

ZGREP(1)						      General Commands Manual							  ZGREP(1)

NAME

       zgrep - search possibly compressed files for a regular expression

SYNOPSIS

       zgrep [ grep_options ] [ -e ] pattern filename...

DESCRIPTION

       Zgrep  invokes  grep  on  compressed  or  gzipped  files.   These  grep	options  will  cause  zgrep  to  terminate  with  an  error  code:
       (-[drRzZ]|--di*|--exc*|--inc*|--rec*|--nu*).  All other options specified are passed directly to grep.  If no file is specified,  then  the
       standard input is decompressed if necessary and fed to grep.  Otherwise the given files are uncompressed if necessary and fed to grep.

       If the GREP environment variable is set, zgrep uses it as the grep program to be invoked.

EXIT CODE

       2 - An option that is not supported was specified.

AUTHOR

       Charles Levert (charles@comm.polymtl.ca)

SEE ALSO

       grep(1), gzexe(1), gzip(1), zdiff(1), zforce(1), zmore(1), znew(1)

																	  ZGREP(1)
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