src/user/cat.nsc

include "syscalls.nsh";
include "lib.nsh";
include "string.nsh";
include "stdio.nsh";
 
/* one arg -- kfs_resolve (by way of fd_open, kernel-side) handles a
 * bare name, a relative path, or an absolute one, so "cat file",
 * "cat doc/x" and "cat /doc/x" all work the same way. the whole file
 * is read in one go by stdio.nsc's read_all, into a buffer sized to
 * the real file (sys_fsize) -- no fixed cap. this used to be one
 * 63488-byte sys_read (kfs's old max file size), which silently cut
 * off anything bigger once kfs grew double indirection.
 *
 * the buffer is sys_alloc'd (inside read_all), not a global array
 * or a stack local: kaboom's single shared 64kib stack (see boot.s)
 * has no room for a big buffer sitting in any one frame, and a
 * global array would exist in every cat process's own .bss whether
 * or not it's ever run -- the whole point of building an arena
 * allocator (see alloc.nsc) was to stop reaching for a fixed-size
 * buffer for something that's really "give me some memory, once, at
 * runtime". */
global i32
main(i32 argc, ptr argv)
{
	ptr fname;
	u64 fname_len;
	i32 fd;
	i64 n;
	ptr buf;
 
	if(argc < 2)
	{
		fputs(2, "usage: cat file\n");
		return 1;
	}
 
	fname = argv_get(argv, 1);
	fname_len = strlen(fname);
	fd = sys_open(fname, fname_len);
	if(fd < 0)
	{
		print_err(2, "cat", "file not found");
		return 1;
	}
 
	buf = read_all(fd, &n);
	sys_close(fd);
	if(buf == (ptr)0)
	{
		print_err(2, "cat", "read failed");
		return 1;
	}
	sys_write(1, buf, (u64)n);
	return 0;
}