查找异常上下文

#!/bin/bash
number=$1;
msg=$1;
file=$2;

if [ $1 ]; then
        msg=$1;
else
        echo "msg is empty";
    exit 1;
fi;

if [ $2 ]; then
        file=$2;
else
        echo "filename is empty";
    exit 2;
fi;


if [ $3 ]; then
    last=$3;
else
    last=5;
fi;


if [ $4 ]; then
    length=$4;
else 
    length=10;
fi;

echo $number,$file;

let "number=$number+5";

echo $number;

list=`cat -n $file | grep -i $msg | cut -f1`

for iter in $list
do
  echo $iter;
  number=$iter;
  let "number=$number+$last";
  head -n $number $file | tail -n $length
done;

# head -n $number $file | tail -n 10