Bell 32V development

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

/* 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
*/
#include        <sys/types.h>
#include        <sys/stat.h>
#include        <errno.h>
#define LBIN 4097
struct  stat    statb;
char bin[LBIN];
int errno;

main(argc,argv)
char **argv;
{
       long n,di;
       int fromend;
       register i,j,k;
       char *p;
       int partial,piped,bylines;
       char *arg;
       lseek(0,(long)0,1);
       piped = errno==ESPIPE;
       arg = argv[1];
       if(argc<=1 || *arg!='-'&&*arg!='+') {
               arg = "-10l";
               argc++;
               argv--;
       }
       fromend = *arg=='-';
       arg++;
       if(!digit(*arg))
               goto errcom;
       n = 0;
       while(digit(*arg))
               n = n*10 + *arg++ - '0';
       if(!fromend&&n>0)
               n--;
       if(argc>2) {
               close(0);
               if(open(argv[2],0)!=0) {
                       write(2,"tail: can't open ",17);
                       write(2,argv[2],strlen(argv[2]));
                       write(2,"\n",1);
                       exit(1);
               }
       }
       bylines = 0;
       switch(*arg) {
       case 'b':
               n <<= 9;
               break;
       case 'c':
               break;
       case '\0':
       case 'l':
               bylines = 1;
               break;
       default:
               goto errcom;
       }
       if(fromend)
               goto keep;

                       /*seek from beginning */

       if(bylines) {
               j = 0;
               while(n-->0) {
                       do {
                               if(j--<=0) {
                                       p = bin;
                                       j = read(0,p,512);
                                       if(j--<=0) exit(0);
                               }
                       } 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>512?512:n;
                               i = read(0,bin,i);
                               if(i<=0) exit(0);
                               n -= i;
                       }
               else
                       lseek(0,n,0);
       }
       while((i=read(0,bin,512))>0)
               write(1,bin,i);
       exit(0);

                       /*seek from end*/

keep:
       if(n<=0) exit(0);
       if(!piped) {
               fstat(0,&statb);
               di = !bylines&&n<LBIN?n:LBIN-1;
               if(statb.st_size > di)
                       lseek(0,-di,2);
       }
       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 {
               k = i;
               j = 0;
               do {
                       do {
                               if(--k<0) {
                                       if(partial)
                                               goto brkb;
                                       k = LBIN -1;
                               }
                       } while(bin[k]!='\n'&&k!=i);
               } while(j++<n&&k!=i);
brkb:
               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);
       }
       exit(0);
errcom:
       write(2,"usage: tail +\b_n[lbc] [file]\n",29);
       exit(1);
}

digit(c)
{
       return(c>='0'&&c<='9');
}