复制代码 代码如下:
#!/bin/bash
#name: upper_to_lower.sh
#the function is trun uper to lower
#like ABCd to abcd

haveuppernumber()
{
    #test if the string have upper number
    str="$(echo $1 | tr '[:upper:]' '[:lower:]')"
    if [ "$str" != $1 ] ; then #get some problem
        echo "[#have upper number,and i well trun them to lower:#]"
        return 1 #have upper number
    else
        return 0 #no upper number
    fi
}

if [ $# -ne 1 ] ; then
    echo "Usage: $0 <string>" >&2
    exit 1
fi

if ! haveuppernumber $1 ; then #when if is 0 it run?
#if [ 0 ] ; then #in shell true return 0 ,false return 1
    echo $1 | tr '[:upper:]' '[:lower:]' #it can turn the UPPER number to lower
#    echo $1 | tr '[:lower:]' '[:upper:]' #it can turn the lower number to UPPER
else
    echo "[#no upper number:#]"
    echo $1
fi

exit 0

功能说明：当输入”./upper_to_lower.sh AaBbCcdd“时会先判断输入格式是否正确，然后判断字符串中是否有大写字母如果有显示"[#have upper number,and i well trun them to lower:#]"和转换成小写字母后的字符串；如果没有大写字母显示"[#no upper number:#]"和小写字符串。

然后又试着用c语言实现相同的功能，如下：

复制代码 代码如下:
#include<stdio.h>
#include<stdlib.h>

int haveuppernumber(char *p)
{
    char*q=p;

    for(;*q!='\0';q++)
    {
        if(*q>='A'&&*q<='Z')
        {
            printf("[#have upper number and i will turn them to lower #]\n");
            return 1;
        }
    }
    printf("[#no upper number#]\n");
    return 0;
}
void turntolower(char *p)
{
    for(;*p != '\0';p++)
    {
        if(*p>='A' && *p<='Z')
        {
            *p+=' ';
        }
    }
}

int main(int argc , char *argv[])
{
    char *p;
    p=argv[1];

    if(argc != 2)
    {
        printf("Usage : %s <string>\n",argv[0]);
        exit(-1);
    }
    if(haveuppernumber(p))
    {
        turntolower(p);
        printf("%s\n",argv[1]);
    }
    else
    {
        printf("%s\n",argv[1]);
    }
    return 0;
}