# /* tail command * * tail where [file] * where is +_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 */ #define LBIN 4097 #define ESPIPE 29 struct { long longint; }; char bin[LBIN]; int *buf bin; int errno; main(argc,argv) char **argv; { long n,di; int fromend; register i,j,k; char *p; int partial,piped,bylines; char *arg; seek(0,0,1); 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 input\n",23); 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,buf); if(piped||(buf[2]&060000)==020000) 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,bin); bin[8] = 0; di = !bylines&&n<LBIN?n:LBIN-1; if(bin[8].longint>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 +_n[lbc] [file]\n",29); exit(1); } digit(c) { return(c>='0'&&c<='9'); }