teddy@toshiba~$ a="76" 
teddy@toshiba~$ echo $((a+3)) 
79 
teddy@toshiba~$ echo $((a-12)) 
64 
teddy@toshiba~$ 



取文件名以及文件路径的脚本： 

#!/bin/sh 
tmp=$1 
filename=`echo $1 | awk -F/ '{print $(NF)}'` 
echo "filename":$filename 
filenamelength=`echo  | awk '{print length("'${filename}'")}' ` 
totallength=`echo  | awk '{print length("'${tmp}'")}' ` 
length=`echo $((totallength-filenamelength))` 
filepath=`echo $tmp | cut -c -$length` 
echo "filepath":$filepath 

调用方式： 

eamon@dxeamon:~/tmp$ sh a.sh 1/2/3/4/5/6 
filename:6 
filepath:1/2/3/4/5/