shell-判断一个目录是否存在，不存在是否创建

#!/bin/bash
is_it_a_directory()#用于判断一个目录是否存在
{
if [ $# -lt 1 ]
then
echo "is_it_a_directory:I need an argument"
return 1
fi
_DIRECTORY_NAME=$1
if [ ! -d $_DIRECTORY_NAME ]
then
return 1
else
return 0
fi

}
#是否创建
echo "enter destination directory:"
read DIREC
if is_it_directory $DIREC >/dev/null 2>&1
then :
else
echo "$DIREC does not exits, create it now?[y..n]"
read choice
if [ "$choice" = "y" ]
then
mkdir $DIREC
echo "create $DIREC ok"
else
echo "see you again"
fi
fi