add directory study

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

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+/* rev - reverse an ASCII line	  Authors: Paul Polderman & Michiel Huisjes */
+
+#include <sys/types.h>
+#include <fcntl.h>
+#include <blocksize.h>
+
+#ifndef EOF
+#define	EOF	((char) -1)
+#endif
+
+
+int fd;				/* File descriptor from file being read */
+
+main(argc, argv)
+int argc;
+char *argv[];
+{
+  register unsigned short i;
+
+  if (argc == 1) {		/* If no arguments given, use stdin as input */
+	fd = 0;
+	rev();
+	exit(0);
+  }
+  for (i = 1; i < argc; i++) {	/* Reverse each line in arguments */
+	if ((fd = open(argv[i], O_RDONLY)) < 0) {
+		std_err("Cannot open ");
+		std_err(argv[i]);
+		std_err("\n");
+		continue;
+	}
+	rev();
+	close(fd);
+  }
+  exit(0);
+}
+
+
+
+
+rev()
+{
+  char output[BLOCK_SIZE];	/* Contains a reversed line */
+  register unsigned short i;	/* Index in output array */
+
+  do {
+	i = BLOCK_SIZE - 1;
+	while ((output[i] = nextchar()) != '\n' && output[i] != EOF) i--;
+	write(1, &output[i + 1], BLOCK_SIZE - 1 - i); /* write reversed line */
+	if (output[i] == '\n')	/* and write a '\n' */
+		write(1, "\n", 1);
+  } while (output[i] != EOF);
+}
+
+
+
+
+char buf[BLOCK_SIZE];
+nextchar()
+{				/* Does a sort of buffered I/O */
+  static int n = 0;		/* Read count */
+  static int i;			/* Index in input buffer to next character */
+
+  if (--n <= 0) {		/* We've had this block. Read in next block */
+	n = read(fd, buf, BLOCK_SIZE);
+	i = 0;			/* Reset index in array */
+  }
+  return((n <= 0) ? EOF : buf[i++]);	/* Return -1 on EOF */
+}