first commit

user/cat.c

@@ -0,0 +1,44 @@
+#include "kernel/types.h"
+#include "kernel/stat.h"
+#include "kernel/fcntl.h"
+#include "user/user.h"
+
+char buf[512];
+
+void
+cat(int fd)
+{
+  int n;
+
+  while((n = read(fd, buf, sizeof(buf))) > 0) {
+    if (write(1, buf, n) != n) {
+      fprintf(2, "cat: write error\n");
+      exit(1);
+    }
+  }
+  if(n < 0){
+    fprintf(2, "cat: read error\n");
+    exit(1);
+  }
+}
+
+int
+main(int argc, char *argv[])
+{
+  int fd, i;
+
+  if(argc <= 1){
+    cat(0);
+    exit(0);
+  }
+
+  for(i = 1; i < argc; i++){
+    if((fd = open(argv[i], O_RDONLY)) < 0){
+      fprintf(2, "cat: cannot open %s\n", argv[i]);
+      exit(1);
+    }
+    cat(fd);
+    close(fd);
+  }
+  exit(0);
+}