awk Search script with prior and following line capability

#!/bin/sh

# *********************************************************

# This uses nawk to list lines coming prior to and after

# the given search string.

# Format: xgrep

# ********************************************************

if [ $# != 4 ]

then

echo "Usage: $0 "

exit

fi

STR=$1

BEF=$2

AFT=$3

while [ ! -z "$4" ] ; do

echo ========== $4

nawk 'c-->0{print NR ":\t" $0;};$0~s{if(b)for(c=b+1;c>1;c--) print (NR-c + 1) ":\t" r[(NR-c+1)%b];print NR ":\t" $0;c=a}b{r[NR%b]=$0;}' b=$BEF a=$AFT s=$STR $4 | sed "s/^/$4\

/"

shift

done

echo ==========

Took me a while to understand how awk worked and customized the command I found on the net for my own needs.