shell 循环往文件某行插入内容

脚本

~]$ cat 1.sh
#!/bin/bash
hang=$(expr `cat 2.txt |wc -l` - 1)
contens=$(egrep ^a aa.txt)
IFS=$'\n\n'
for i in $contens
do
    sed -i "$hang a $i" 2.txt
    hang=$(expr $hang + 1)
done

文件

~]$ cat 2.txt
1
2
3
aaasdkhfla2347923 askdf
akjdfg87998fgsdfg
4


~]$ cat aa.txt
aaasdkhfla2347923 askdf
akjdfg87998fgsdfg
b2387sdkjlfsjdf