Minix1.1/usr/src/commands/rev.c

/* rev - reverse an ASCII line	  Authors: Paul Polderman & Michiel Huisjes */

#include "blocksize.h"

#ifndef NULL
#define	NULL	0
#endif

#ifndef EOF
#define	EOF	((char) -1)
#endif


int fd;			/* File descriptor from file currently being read */

main(argc, argv)
int argc;
char *argv[];
{
  register unsigned short i;

  if (argc == 1) {	/* If no arguments given, take stdin as input */
  	fd = 0;
  	rev();
  	exit(0);
  }
  for (i = 1; i < argc; i++) {	/* Reverse each line in arguments */
  	if ((fd = open(argv[i], 0)) < 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 */
}