shell脚本---回文检测

#! /bin/bash
read -p "Please input a string:" word
#echo $word
num=${#word}
echo

let a=num%2
let b=num/2

for((i=0;i<b;i++))
{
pattern=$pattern'\(.\)'
}
echo $pattern

if [ $a -ne 0 ];
then
pattern=$pattern'.'
fi
echo $pattern

for((i=b;i>0;i--))
do
pattern=$pattern"\\$i"
done
pattern='/'$pattern'/p'
echo $pattern

echo $word | sed -n "$pattern"
echo

#! /bin/bash
read -p "input:" word
rword=`echo $word | rev`
if [ $word = $rword ];
then
echo YES
else
echo NO
fi