date and time created 80/10/06 23:53:23 by root

[unix-history] / usr / src / usr.bin / tail / tail.c

static char *sccsid = "@(#)tail.c       4.1 (Berkeley) %G%";
/* tail command 
*
*      tail where [file]
*      where is +\b_n[type]
*      - means n lines before end
*      + means nth line from beginning
*      type 'b' means tail n blocks, not lines
*      type 'c' means tail n characters
*      Type 'r' means in lines in reverse order from end
*       (for -r, default is entire buffer )
*      option 'f' means loop endlessly trying to read more
*              characters after the end of file, on the  assumption
*              that the file is growing
*/

#include        <stdio.h>
#include        <ctype.h>
#include        <sys/types.h>
#include        <sys/stat.h>
#include        <errno.h>

#define LBIN 4097
struct  stat    statb;
int     follow;
int     piped;
char bin[LBIN];
int errno;

main(argc,argv)
char **argv;
{
       long n,di;
       register i,j,k;
       char    *arg;
       int partial,bylines,bkwds,fromend,lastnl;
       char *p;

       lseek(0,(long)0,1);
       piped = errno==ESPIPE;
       arg = argv[1];
       if(argc<=1 || *arg!='-'&&*arg!='+') {
               arg = "-10l";
               argc++;
               argv--;
       }
       fromend = *arg=='-';
       arg++;
       n = 0;
       while(isdigit(*arg))
               n = n*10 + *arg++ - '0';
       if(!fromend&&n>0)
               n--;
       if(argc>2) {
               close(0);
               if(open(argv[2],0)!=0) {
                       perror(argv[2]);
                       exit(1);
               }
       }
       bylines = -1; bkwds = 0;
       while(*arg)
       switch(*arg++) {

       case 'b':
               n <<= 9;
               if(bylines!=-1) goto errcom;
               bylines=0;
               break;
       case 'c':
               if(bylines!=-1) goto errcom;
               bylines=0;
               break;
       case 'f':
               follow = 1;
               break;
       case 'r':
               if(n==0) n = LBIN;
               bkwds = 1; fromend = 1; bylines = 1;
               break;
       case 'l':
               if(bylines!=-1) goto errcom;
               bylines = 1;
               break;
       default:
               goto errcom;
       }
       if (n==0) n = 10;
       if(bylines==-1) bylines = 1;
       if(bkwds) follow=0;
       if(fromend)
               goto keep;

                       /*seek from beginning */

       if(bylines) {
               j = 0;
               while(n-->0) {
                       do {
                               if(j--<=0) {
                                       p = bin;
                                       j = read(0,p,BUFSIZ);
                                       if(j--<=0)
                                               fexit();
                               }
                       } while(*p++ != '\n');
               }
               write(1,p,j);
       } else  if(n>0) {
               if(!piped)
                       fstat(0,&statb);
               if(piped||(statb.st_mode&S_IFMT)==S_IFCHR)
                       while(n>0) {
                               i = n>BUFSIZ?BUFSIZ:n;
                               i = read(0,bin,i);
                               if(i<=0)
                                       fexit();
                               n -= i;
                       }
               else
                       lseek(0,n,0);
       }
copy:
       while((i=read(0,bin,BUFSIZ))>0)
               write(1,bin,i);
       fexit();

                       /*seek from end*/

keep:
       if(n <= 0)
               fexit();
       if(!piped) {
               fstat(0,&statb);
               di = !bylines&&n<LBIN?n:LBIN-1;
               if(statb.st_size > di)
                       lseek(0,-di,2);
               if(!bylines)
                       goto copy;
       }
       partial = 1;
       for(;;) {
               i = 0;
               do {
                       j = read(0,&bin[i],LBIN-i);
                       if(j<=0)
                               goto brka;
                       i += j;
               } while(i<LBIN);
               partial = 0;
       }
brka:
       if(!bylines) {
               k =
                   n<=i ? i-n:
                   partial ? 0:
                   n>=LBIN ? i+1:
                   i-n+LBIN;
               k--;
       } else {
               if(bkwds && bin[i==0?LBIN-1:i-1]!='\n'){        /* force trailing newline */
                       bin[i]='\n';
                       if(++i>=LBIN) {i = 0; partial = 0;}
               }
               k = i;
               j = 0;
               do {
                       lastnl = k;
                       do {
                               if(--k<0) {
                                       if(partial) {
                                               if(bkwds) write(1,bin,lastnl+1);
                                               goto brkb;
                                       }
                                       k = LBIN -1;
                               }
                       } while(bin[k]!='\n'&&k!=i);
                       if(bkwds && j>0){
                               if(k<lastnl) write(1,&bin[k+1],lastnl-k);
                               else {
                                       write(1,&bin[k+1],LBIN-k-1);
                                       write(1,bin,lastnl+1);
                               }
                       }
               } while(j++<n&&k!=i);
brkb:
               if(bkwds) exit(0);
               if(k==i) do {
                       if(++k>=LBIN)
                               k = 0;
               } while(bin[k]!='\n'&&k!=i);
       }
       if(k<i)
               write(1,&bin[k+1],i-k-1);
       else {
               write(1,&bin[k+1],LBIN-k-1);
               write(1,bin,i);
       }
       fexit();
errcom:
       fprintf(stderr, "usage: tail [+\b_[n][lbc][rf]] [file]\n");
       exit(2);
}

fexit()
{       register int n;
       if (!follow || piped) exit(0);
       for (;;)
       {       sleep(1);
               while ((n = read (0, bin, BUFSIZ)) > 0)
                       write (1, bin, n);
       }
}