/* 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 */ #include <sys/types.h> #include <sys/stat.h> #include <errno.h> #include <pagsiz.h> #define BUFSIZ BSIZE #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,BUFSIZ); 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>BUFSIZ?BUFSIZ:n; i = read(0,bin,i); if(i<=0) exit(0); n -= i; } else lseek(0,n,0); } while((i=read(0,bin,BUFSIZ))>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 +_n[lbc] [file]\n",29); exit(1); } digit(c) { return(c>='0'&&c<='9'); }