main.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#define	EXTERN
#include	"grep.h"

char *validflags = "bchiLlnsv";
void
usage(void)
{
	fprint(2, "usage: grep [-%s] [-e pattern] [-f patternfile] [file ...]\n", validflags);
	exits("usage");
}

void
main(int argc, char *argv[])
{
	int i, status;

	ARGBEGIN {
	default:
		if(utfrune(validflags, ARGC()) == nil)
			usage();
		flags[ARGC()]++;
		break;

	case 'e':
		flags['e']++;
		lineno = 0;
		str2top(EARGF(usage()));
		break;

	case 'f':
		flags['f']++;
		filename = EARGF(usage());
		rein = Bopen(filename, OREAD);
		if(rein == 0) {
			fprint(2, "grep: can't open %s: %r\n", filename);
			exits("open");
		}
		lineno = 1;
		str2top(filename);
		break;
	} ARGEND

	if(flags['f'] == 0 && flags['e'] == 0) {
		if(argc <= 0)
			usage();
		str2top(argv[0]);
		argc--;
		argv++;
	}

	follow = mal(maxfollow*sizeof(*follow));
	state0 = initstate(topre.beg);

	Binit(&bout, 1, OWRITE);
	switch(argc) {
	case 0:
		status = search(0, 0);
		break;
	case 1:
		status = search(argv[0], 0);
		break;
	default:
		status = 0;
		for(i=0; i<argc; i++)
			status |= search(argv[i], Hflag);
		break;
	}
	if(status)
		exits(0);
	exits("no matches");
}

int
search(char *file, int flag)
{
	State *s, *ns;
	int c, fid, eof, nl, empty;
	long count, lineno, n;
	uchar *elp, *lp, *bol;

	if(file == 0) {
		file = "stdin";
		fid = 0;
		flag |= Bflag;
	} else
		fid = open(file, OREAD);

	if(fid < 0) {
		fprint(2, "grep: can't open %s: %r\n", file);
		return 0;
	}

	if(flags['b'])
		flag ^= Bflag;		/* dont buffer output */
	if(flags['c'])
		flag |= Cflag;		/* count */
	if(flags['h'])
		flag &= ~Hflag;		/* do not print file name in output */
	if(flags['i'])
		flag |= Iflag;		/* fold upper-lower */
	if(flags['l'])
		flag |= Llflag;		/* print only name of file if any match */
	if(flags['L'])
		flag |= LLflag;		/* print only name of file if any non match */
	if(flags['n'])
		flag |= Nflag;		/* count only */
	if(flags['s'])
		flag |= Sflag;		/* status only */
	if(flags['v'])
		flag |= Vflag;		/* inverse match */

	s = state0;
	lineno = 0;
	count = 0;
	eof = 0;
	empty = 1;
	nl = 0;
	lp = u.buf;
	bol = lp;

loop0:
	n = lp-bol;
	if(n > sizeof(u.pre))
		n = sizeof(u.pre);
	memmove(u.buf-n, bol, n);
	bol = u.buf-n;
	n = read(fid, u.buf, sizeof(u.buf));
	/* if file has no final newline, simulate one to emit matches to last line */
	if(n > 0) {
		empty = 0;
		nl = u.buf[n-1]=='\n';
	} else {
		if(n < 0){
			fprint(2, "grep: read error on %s: %r\n", file);
			return count != 0;
		}
		if(!eof && !nl && !empty) {
			u.buf[0] = '\n';
			n = 1;
			eof = 1;
		}
	}
	if(n <= 0) {
		close(fid);
		if(flag & Cflag) {
			if(flag & Hflag)
				Bprint(&bout, "%s:", file);
			Bprint(&bout, "%ld\n", count);
		}
		if(((flag&Llflag) && count != 0) || ((flag&LLflag) && count == 0))
			Bprint(&bout, "%s\n", file);
		Bflush(&bout);
		return count != 0;
	}
	lp = u.buf;
	elp = lp+n;
	if(flag & Iflag)
		goto loopi;

/*
 * normal character loop
 */
loop:
	c = *lp;
	ns = s->next[c];
	if(ns == 0) {
		increment(s, c);
		goto loop;
	}
//	if(flags['2'])
//		if(s->match)
//			print("%d: %.2x**\n", s, c);
//		else
//			print("%d: %.2x\n", s, c);
	lp++;
	s = ns;
	if(c == '\n') {
		lineno++;
		if(!!s->match == !(flag&Vflag)) {
			count++;
			if(flag & (Cflag|Sflag|Llflag|LLflag))
				goto cont;
			if(flag & Hflag)
				Bprint(&bout, "%s:", file);
			if(flag & Nflag)
				Bprint(&bout, "%ld: ", lineno);
			/* suppress extra newline at EOF unless we are labeling matches with file name */
			Bwrite(&bout, bol, lp-bol-(eof && !(flag&Hflag)));
			if(flag & Bflag)
				Bflush(&bout);
		}
		if((lineno & Flshcnt) == 0)
			Bflush(&bout);
	cont:
		bol = lp;
	}
	if(lp != elp)
		goto loop;
	goto loop0;

/*
 * character loop for -i flag
 * for speed
 */
loopi:
	c = *lp;
	if(c >= 'A' && c <= 'Z')
		c += 'a'-'A';
	ns = s->next[c];
	if(ns == 0) {
		increment(s, c);
		goto loopi;
	}
	lp++;
	s = ns;
	if(c == '\n') {
		lineno++;
		if(!!s->match == !(flag&Vflag)) {
			count++;
			if(flag & (Cflag|Sflag|Llflag|LLflag))
				goto conti;
			if(flag & Hflag)
				Bprint(&bout, "%s:", file);
			if(flag & Nflag)
				Bprint(&bout, "%ld: ", lineno);
			/* suppress extra newline at EOF unless we are labeling matches with file name */
			Bwrite(&bout, bol, lp-bol-(eof && !(flag&Hflag)));
			if(flag & Bflag)
				Bflush(&bout);
		}
		if((lineno & Flshcnt) == 0)
			Bflush(&bout);
	conti:
		bol = lp;
	}
	if(lp != elp)
		goto loopi;
	goto loop0;
}

State*
initstate(Re *r)
{
	State *s;
	int i;

	addcase(r);
	if(flags['1'])
		reprint("r", r);
	nfollow = 0;
	gen++;
	fol1(r, Cbegin);
	follow[nfollow++] = r;
	qsort(follow, nfollow, sizeof(*follow), fcmp);

	s = sal(nfollow);
	for(i=0; i<nfollow; i++)
		s->re[i] = follow[i];
	return s;
}