4.3-cat-命令的实现.md

在内核中我们用到了很多很多命令，比如ls ,cat ,mkdir 下面我们来实现一个cat命令

//-------------------------------------------------------------------
//	mycat.c
//
//	This program shows how the default behavior of the standard
//	UNIX/Linux 'cat' command could readily be implemented in C.  
//	(Consult the 'man' page for 'cat' to see the 'options' that 
//	would need to be added to achieve a total 'cat' emulation.)
//
//		compile using:  $ gcc mycat.c -o mycat
//		execute using:  $ ./mycat <filename>
//
//	programmer: ALLAN CRUSE
//	written on: 24 AUG 2007
//-------------------------------------------------------------------
#include <fcntl.h>	// for open() 
#include <stdio.h>	// for perror() 
#include <unistd.h>	// for read(), write(), close() 
int main( int argc, char *argv[] )
{
	int	i, fd, ch;	// declare local variables
	for (i = 1; i < argc; i++)
		{
		fd = open( argv[i], O_RDONLY );
		if ( fd < 0 ) { perror( argv[i] ); continue; }
		while ( read( fd, &ch, 1 ) == 1 ) 
			write( STDOUT_FILENO, &ch, 1 );
		close( fd );
		}
}

将上述文件保存为mycat.c

$ make mycat
$ ./mycat mycat.c

它的效果如下：