如何使用php删除目录中的旧文件(how to delete old files in a directory using php)

 由于这个问题被标记为Linux和Unix，我将对David Scwartz所说的内容进行一些扩展，简而言之，就是“操作系统中有一个API”。 Windows的相同基本原理也适用，但实际的实现是不同的，尽管我怀疑操作系统内部的实现是一样的，但没有真正的方法可以知道，因为我们无法检查Windows的源代码（然而，人们可以理解操作系统和处理器的工作原理，并找出必须发生的事情！） 
 
 Linux有一个名为ptrace的函数，它允许一个进程（在检查特权之后）以各种方式检查另一个进程。 这是一个电话，但第一个参数是“你想做什么”。 以下是一些最基本的例子 - 对于较少的“常见”操作，有几十个其他例子： 
 
 
 
 PTRACE_ATTACH - 连接到进程。 
 
 
 PTRACE_PEEKTEXT - 查看附加进程的代码内存（例如，反汇编代码） 
 
 
 PTRACE_PEEKDATA - 查看附加进程的'数据存储器（显示变量） 
 
 
 PTRACE_POKETEXT - 写入进程的代码内存 
 
 
 PTRACE_POKEDATA - 写入进程'数据存储器。 
 
 
 PTRACE_GETREGS - 复制当前寄存器值。 
 
 
 PTRACE_SETREGS - 更改当前的寄存器值（例如，如果x恰好在寄存器中，则set variable x = 7的调试命令） 
 
 
 在Linux中，由于内存“完全相同”， PTRACE_PEEKTEXT和PTRACE_PEEKDATA实际上是相同的功能，所以你可以在PTRACE_PEEKDATA代码中PTRACE_PEEKDATA一个地址，例如，在PTRACE_PEEKTEXT的堆栈上给一个地址，它将完全愉快地复制回来为你。 区别在于OS /处理器组合，其中存储器在DATA存储器和CODE存储器之间“分离”。 大多数现代操作系统和处理器都没有做出这种区分。 同样明显适用于PTRACE_POKEDATA和PTRACE_POKETEXT 。 
 
 所以，假设“调试程序”使用： 
 
long data = ptrace(PTRACE_PEEKDATA, pid, 0x12340128, NULL); 
 
 当使用PTRACE_PEEKDATA为地址0x12340128调用OS时，它将“查看”内存的相应内存映射，位于0x12340128（页面对齐，使得0x12340000），如果存在，它将被映射到内核，数据是然后从地址0x12340128复制到本地存储器，内存未映射，复制的数据作为返回值传回。 
 
 该手册规定使用的启动如下： 
 
 
 
 父进程可以通过调用fork（2）并让生成的子进行PTRACE_TRACEME来启动跟踪，然后（通常）执行exec（3）。 或者，父母可以使用PTRACE_ATTACH开始跟踪现有过程。 
 
 
 对于几页，有关man ptrace更多信息。 

Since the question is tagged Linux and Unix, I'll expand a little on what David Scwartz says, which in short is "there is an API for that in the OS". The same basic principle applies in Windows as well, but the actual implementation is different, and although I suspect the implementation inside the OS does the same thing, there's no REAL way to know that, since we can't inspect the source code for Windows (one can, however, understanding how an OS and a processor works, sort of figure out what must be happening!)
 
Linux has a function called ptrace, that allows one process (following some checking of privileges) to inspect another process in various ways. It is one call, but the first parameter is a "what do you want to do". Here are some of the most basic examples - there are a couple of dozen others for less "common" operations:
 
 
 
PTRACE_ATTACH - connect to the process. 
 
 
PTRACE_PEEKTEXT - look at the attached process' code memory (for example to disassemble the code)
 
 
PTRACE_PEEKDATA - look at the attached process' data memory (to display variables)
 
 
PTRACE_POKETEXT - write to process' code memory
 
 
PTRACE_POKEDATA - write to process' data memory.
 
 
PTRACE_GETREGS - copy the current register values. 
 
 
PTRACE_SETREGS - change the current register values (e.g. a debug command of set variable x = 7, if x happens to be in a register) 
 
 
In Linux, since memory is "all the same", PTRACE_PEEKTEXT and PTRACE_PEEKDATA are actually the same functionality, so you can give an address in code for PTRACE_PEEKDATA and an address, say, on the stack for PTRACE_PEEKTEXT and it will perfectly happily copy that back for you. The distinction is made for OS/processor combinations where memory is "split" between DATA memory and CODE memory. Most modern OS's and processors do not make that distinction. Same obviously applies to PTRACE_POKEDATA and PTRACE_POKETEXT.
 
So, say that the "debugger process" uses:
 
long data = ptrace(PTRACE_PEEKDATA, pid, 0x12340128, NULL); 
 
When the OS is called with a PTRACE_PEEKDATA for address 0x12340128 it will "look" at the corresponding memory mapping for the memory at 0x12340128 (page-aligned that makes 0x12340000), if it exists, it will get mapped into the kernel, the data is then copied out from address 0x12340128 into the local memory, the memory unmapped, and the copied data passed back as the return value. 
 
The manual states the initiating of the usage as: 
 
 
 
The parent can initiate a trace by calling fork(2) and having the resulting child do a PTRACE_TRACEME, followed (typically) by an exec(3). Alternatively, the parent may commence trace of an existing process using PTRACE_ATTACH.
 
 
For several pages more information do man ptrace.