add directory study

study/linux-travel/MINIX-1.5/1.5/Source/commands/head.c

@@ -0,0 +1,70 @@
+/* head - print the first few lines of a file	Author: Andy Tanenbaum */
+
+#include <stdio.h>
+
+#define DEFAULT 10
+
+main(argc, argv)
+int argc;
+char *argv[];
+{
+  FILE *f;
+  int n, k, nfiles;
+  char *ptr;
+
+  /* Check for flag.  Only flag is -n, to say how many lines to print. */
+  k = 1;
+  ptr = argv[1];
+  n = DEFAULT;
+  if (argc > 1 && *ptr++ == '-') {
+	k++;
+	n = atoi(ptr);
+	if (n <= 0) usage();
+  }
+  nfiles = argc - k;
+
+  if (nfiles == 0) {
+	/* Print standard input only. */
+	do_file(n, stdin);
+	exit(0);
+  }
+
+  /* One or more files have been listed explicitly. */
+  while (k < argc) {
+	if (nfiles > 1) printf("==> %s <==\n", argv[k]);
+	if ((f = fopen(argv[k], "r")) == NULL)
+		printf("head: cannot open %s\n", argv[k]);
+	else {
+		do_file(n, f);
+		fclose(f);
+	}
+	k++;
+	if (k < argc) printf("\n");
+  }
+  exit(0);
+}
+
+
+
+do_file(n, f)
+int n;
+FILE *f;
+{
+  int c;
+
+  /* Print the first 'n' lines of a file. */
+  while (n) switch (c = getc(f)) {
+	    case EOF:
+		return;
+	    case '\n':
+		--n;
+	    default:	putc((char) c, stdout);
+	}
+}
+
+
+usage()
+{
+  fprintf(stderr, "Usage: head [-n] [file ...]\n");
+  exit(1);
+}