练习1：输入一个数，实现倒叙123-》321

练习2：输入一个，判断是否是素数

练习3：输入一个文件名，
判断是否在家目录下存在,
如果是一个目录，则直接输出是目录下的sh文件的个数
如果存在则判断是否是一个普通文件，如果是普通文件则判断是否具备
可读可写可执行权限，如果具备权限，写入helo.不具备权限，则添加读写执行权限，写入hello
 

#!/bin/bash

read -p "请输入文件名：" a
if [ -e $a ] #默认是家目录下
then
	echo "$a存在"
	#
	if [ -b $a ]
	then
		echo "块设备文件"
		if [ -r $a ]
		then
			echo  -n "r"
		else
			echo -n "-"
		fi
		if [ -w $a ]
		then
			echo -n "w"
		else
			echo -n "-"
		fi
		if [ -x $a ]
		then
			echo -n "x"
		else
			echo -n "-"
		fi
	#
	elif [ -c $a ]
	then
		echo "字符文件"
		if [ -r $a ]
		then
			echo  -n "r"
		else
			echo -n "-"
		fi
		if [ -w $a ]
		then
			echo -n "w"
		else
			echo -n "-"
		fi
		if [ -x $a ]
		then
			echo -n "x"
		else
			echo -n "-"
		fi
	#
	elif [ -d $a ]
	then
		echo "目录文件"
		if [ -r $a ]
		then
			echo  -n "r"
		else
			echo -n "-"
		fi
		if [ -w $a ]
		then
			echo -n "w"
		else
			echo -n "-"
		fi
		if [ -x $a ]
		then
			echo -n "x"
		else
			echo -n "-"
		fi
	#
	elif [ -L $a ]
	then
		echo "软链接文件"
		if [ -r $a ]
		then
			echo  -n "r"
		else
			echo -n "-"
		fi
		if [ -w $a ]
		then
			echo -n "w"
		else
			echo -n "-"
		fi
		if [ -x $a ]
		then
			echo -n "x"
		else
			echo -n "-"
		fi
	#
	elif [ -S $a ]
	then
		echo "套接字文件"
		if [ -r $a ]
		then
			echo  -n "r"
		else
			echo -n "-"
		fi
		if [ -w $a ]
		then
			echo -n "w"
		else
			echo -n "-"
		fi
		if [ -x $a ]
		then
			echo -n "x"
		else
			echo -n "-"
		fi

	elif [ -p $a ]
	then
		echo "管道文件"
		if [ -r $a ]
		then
			echo  -n "r"
		else
			echo -n "-"
		fi
		if [ -w $a ]
		then
			echo -n "w"
		else
			echo -n "-"
		fi
		if [ -x $a ]
		then 
			echo -n "x"
		else
			echo -n "-"
		fi

	elif [ -f $a ]
	then
		echo "普通文件"
		if [ -r $a ]
		then
			echo  -n "r"
		else
			echo -n "-"
		fi
		if [ -w $a ]
		then 
			echo -n "w"
		else
			echo -n "-"
		fi
		if [ -x $a ]
		then
			echo -n "x"
		else
			echo -n "-"
		fi

	fi
else
	echo "$a不存在"
fi

 

练习4：输入一个字符串，实现字符串逆置