tail

/* tail - print the end of a file */

#include "stdio.h"
#define TRUE 1
#define FALSE 0
#define BLANK ' '
#define TAB '\t'
#define NEWL '\n'

int lines, chars ;
char buff[BUFSIZ];

main(argc, argv)
int argc ;
char *argv[] ;
{
        char *s ;
        FILE *input , *fopen();
        int count ;


	setbuf(stdout, buff);
        argc-- ; argv++ ;
        lines = TRUE ;
        chars = FALSE ;
        count = -10 ;

        if (argc == 0 ) {
                tail(stdin, count);
                done(0) ;
        }

        s = *argv ;
        if (*s == '-' || *s == '+' ) {
                s++ ;
                if (*s >= '0' && *s <= '9' ) {
                        count = stoi(*argv);
                        s++ ;
                        while (*s >= '0' && *s <= '9' )
                                s++ ;
                }
                if (*s == 'c' ) {
                        chars = TRUE ;
                        lines = FALSE ;
                }
                else if (*s != 'l' && *s != NULL ) {
                        fprintf(stderr, "tail: unknown option %c\n", *s);
                        argc = 0 ;
                }
                argc-- ; argv++ ;
        }

        if (argc < 0 ) {
                fprintf(stderr, "Usage: tail [+/-[number][lc]] [files]\n");
                done(1) ;
        }

        if (argc == 0 )
                tail(stdin, count);

        else if ((input=fopen(*argv,"r")) == NULL ) {
                fprintf(stderr, "tail: can't open %s\n", *argv) ;
                done(1) ;
        }
        else {
                tail(input, count);
                fclose(input);
        }

        done(0) ;
}

/* stoi - convert string to integer */

stoi(s)
char *s ;
{
        int n, sign ;

        while (*s == BLANK || *s == NEWL || *s == TAB )
                s++ ;

        sign = 1 ;
        if (*s == '+' )
                s++ ;
        else if (*s == '-' ) {
                sign = -1 ;
                s++ ;
        }
        for(n=0 ; *s >= '0' && *s <= '9' ; s++ )
                n = 10 * n + *s - '0' ;
        return(sign * n);
}

/* tail - print 'count' lines/chars */

#define INCR(p)  if (p >= end) p=cbuf ; else p++
#define BUF_SIZE 4098

char cbuf[ BUF_SIZE ] ;

tail(in, goal )
FILE *in ;
int goal ;
{
        int c, count ;
        char *start, *finish, *end ;

        count = 0 ;

        if (goal > 0 ) {        /* skip */

                if (lines )             /* lines */
                        while ((c=getc(in)) != EOF ) {
                                if (c == NEWL )
                                        count++ ; 
                                if (count >= goal )
                                        break ;
                        }
                else                    /* chars */
                        while (getc(in) != EOF ) {
                                count++ ;
                                if (count >= goal )
                                        break ;
                        }
                if (count >= goal )
                        while ((c=getc(in)) != EOF )
                                putc(c, stdout);
        }

        else {                          /* tail */

                goal = -goal ;
                start = finish = cbuf ;
                end = &cbuf[ BUF_SIZE - 1 ] ;

                while ((c=getc(in)) != EOF ) {
                        *finish = c ;
                        INCR(finish);

                        if (start == finish )
                                INCR(start);
                        if (!lines || c == NEWL )
                                count++ ;

                        if (count > goal ) {
                                count = goal ;
                                if (lines )
                                        while (*start != NEWL )
                                                INCR(start);
                                INCR(start);
                        }

                } /* end while */

                while (start != finish ) {
                        putc(*start, stdout);
                        INCR(start);
                }

        } /* end else */

} /* end tail */



done(n)
int n;
{
  _cleanup();			/* flush stdio's internal buffers */
  exit(n);
}