sehll中函数返回值范围

通过下面的例子可以测试出shell中函数return的返回值为0--255
#!/bin/bash
#find the max one of two numbers
PARAM_ERR=256
PARAM_EQU=0
max2 ()
{
    if [ -z "$2" ]
    then
    return $PARAM_ERR
    fi
    
    if [ "$1" -eq "$2" ]
    then
    return $PARAM_EQU
    fi

    if [ "$1" -gt "$2" ]
    then
    return $1
    else
    return $2
    fi
}

max2 98 88
return_val=$?
if [ "$return_val" -eq "$PARAM_ERR" ]
then
echo "Need parameter"
elif [ "$return_val" -eq "$PARAM_EQU" ]
then
echo "They are equal"
else
echo "The max number is $return_val"
fi