将文件从指定行读取到另一行

I currently have a shell script in C that takes a command of a file, two numbers, mth line and nth line, and supposedly should output whats in between those lines:

我目前在C中有一个shell脚本，它接受一个文件，两个数字，第m行和第n行的命令，并且应该在这些行之间输出什么：

for example:

例如：

./output file1 2 6

would output file from line 2 to line 6

将文件从第2行输出到第6行

I have it implemented currently in a way of outputting the whole file, I have been trying to change it to output specifically between those lines

我目前以输出整个文件的方式实现它，我一直在尝试将其更改为在这些行之间具体输出

this is my code

这是我的代码

#include <fcntl.h>

int main(int argc, char *argv[])
{
    int file;
    int size;
    int l[1000];

    int firstNum = atoi(argv[2]);

    int secondNum = atoi(argv[3]);


    file = open(argv[1], O_RDONLY);

    if( file == -1)
    {
        printf("\n cannot open file \n");
    }

    while ((size=read(file,l,80)) > 0)
        write(1,l,size);




}

I tried to change l and size to firstNum and secondNum, which are the numbers entered from the command line, but still did not work and outputted one single line.

我试图将l和size更改为firstNum和secondNum，这是从命令行输入的数字，但仍然无法工作并输出一行。

What is a better way of doing so ?

这样做的更好方法是什么？

2 个解决方案

#1

There are several issues with your code, so just go through them sequentially:

您的代码存在几个问题，因此请按顺序执行：

It's better to use high level fopen rather than low level open to open a file. So it's better to write this way:

最好使用高级fopen而不是低级open来打开文件。所以最好这样写：
```
FILE *file = fopen(argv[1], "r");
if (file == NULL)
    exit(EXIT_FAILURE);
```
Your read is wrong as it reads exactly 80 characters instead of a line as you expect.

您的读取错误，因为它正好可以读取80个字符而不是您期望的行。
```
while ((size=read(file,l,80)) > 0)   // <-- WRONG because this reads 80 chars instead of one line
```
For similar reason as with open, it's better to use alternative like printf instead of low level read and write.

出于与open相似的原因，最好使用类似printf的替代方法而不是低级读写。
To read line by line, you should use library function getline.

要逐行阅读，您应该使用库函数getline。
To control what line number to print, a simple way is to have a variable tracking what line number and compare with your command line arguments.

要控制要打印的行号，一种简单的方法是使用变量跟踪行号并与命令行参数进行比较。

So put them together, you would need something like this:

所以把它们放在一起，你需要这样的东西：

FILE *file = fopen(argv[1], "r");
if (file == NULL)
    exit(EXIT_FAILURE);

int line_num = 0;

char * line = NULL;
size_t len = 0;
ssize_t read = 0;
while ((read = getline(&line, &len, file)) != -1)
{
    line_num++;
    if( firstNum <= line_num && line_num <= secondNum )
    {
        printf( "line %d: %s", line_num, line );
        if( line_num == secondNum )
            break;
    }
}

#2

Try looking at this post: C read file line by line

试着看这篇文章：C逐行读取文件

From there it should be a simple matter of counting lines read and discarding them until you have read firstNum lines at which point print until you've reached secondNum.

从那里开始计算行读数并丢弃它们应该是一个简单的事情，直到你读取firstNum行，然后打印到你的secondNum。

#1