Shell Programming and Scripting

$ 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

$