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    Length: 4622 (0x120e)
    Types: TextFile
    Notes: UNIX file
    Names: »head.c«

└─⟦f27320a65⟧ Bits:30001972 Commodore 900 hard disk image with partial source code
    └─⟦f4b8d8c84⟧ UNIX V7 Filesystem
        └─ ⟦this⟧ »cmd/head.c« 

TextFile

/*
 * The program head copys the head of a file to the standard output.
 * Its usage is:
 *	head [{+-}n[{lbc}]] [file]
 * The initial `+' (or `-') indicate that `n' is relative to the
 * beggining (or ending respectively) of the file.
 * The optional `l', `b' or `c' (`l' default) is to indicate if `n'
 * is a number of lines, blocks or characters respectively.
 * If the entire position specifier is absent, then `+4l' is assumed.
 * If the optional `file' is absent, then the standard input is used.
 * In any case, head copys from the start of the file up to, and
 * includeing, the specified point onto the standard output.
 */
#include <stdio.h>
#include <ctype.h>
#include <mdata.h>


#define	bool	char			/* boolean type */
#define	not	!			/* logical negation operator */
#define	and	&&			/* logical conjunction */
#define	or	||			/* logical disjunction */
#define	TRUE	(0 == 0)
#define	FALSE	(not TRUE)
#define	EOS	'\0'			/* end-of-string char */
#define	N	4			/* default number of lines */


struct	blk {
	struct blk	*next;
	int		nlines;		/* number of `\n' characters */
	char		blkb[BUFSIZ];
};


bool	lflag	= TRUE,			/* lines (vs. chars) flag */
	fflag	= TRUE;			/* + (vs. -) flag */
long	n	= N;			/* number of lines or chars */
char	obuf[BUFSIZ],			/* stdout setbuf buffer */
	nospace[]	= "Window too large";


main(argc, argv)
int	argc;
char	*argv[];
{
	setbuf(stdout, obuf);
	options(argv);
	if (fflag)
		if (lflag)
			copyfl();
		else
			copyfc();
	else
		if (lflag)
			copybl();
		else
			copybc();
	return (0);
}


die(str)
char	*str;
{
	fprintf(stderr, "%r\n", &str);
	exit(1);
}


usage()
{
	die("usage: head [{+-}n[{lbc}]] [file]");
}


options(argv)
register char	*argv[];
{
	register char	*chp,
			ch;

	if (*++argv == NULL)
		return;
	chp = *argv;
	ch = *chp;
	if (ch == '-'  ||  ch == '+') {
		fflag = (ch == '+');
		n = 0;
		for (ch=*++chp; isascii(ch) && isdigit(ch); ch=*++chp)
			n = 10*n + ch-'0';
		switch (ch) {
		case EOS:
		case 'l':
			break;
		case 'b':
			n *= BUFSIZ;
			/* fall thru */
		case 'c':
			lflag = FALSE;
			break;
		default:
			usage();
		}
		chp = *++argv;
	}
	if (chp == NULL)
		return;
	if (freopen(chp, "r", stdin) == NULL)
		die("Can't open %s", chp);
}


/*
 * Copyfl copys the first `n' lines of stdin to stdout.
 */
copyfl()
{
	register int	ch;

	while (--n >= 0)
		do {
			ch = getchar();
			if (ch == EOF)
				return;
			putchar(ch);
		} while (ch != '\n');
}


/*
 * Copyfc copys the first `n' characters of stdin to stdout.
 */
copyfc()
{
	register int	ch;

	for (ch=getchar(); --n >= 0  &&  ch != EOF; ch=getchar())
		putchar(ch);
}


/*
 * Copybc copys all but the last `n' characters of stdin to stdout.
 */
copybc()
{
	register char	*buf,
			*chp,
			*limit;
	char		ch;
	unsigned	len;

	if (n > MAXUINT)
		die(nospace);
	len = n;
	buf = (char *)malloc(len);
	if (buf == NULL)
		die(nospace);
	len = fread(buf, sizeof *buf, len, stdin);
	if (len < n) {
		fwrite(buf, sizeof *buf, len, stdout);
		free(buf);
		return;
	}
	limit = buf + len;
	for (chp=buf; (ch=getchar()) != EOF;) {
		putchar(*chp);
		*chp++ = ch;
		if (chp == limit)
			chp = buf;
	}
}


/*
 * Copybl copys all but the last `n' lines of stdin to stdout.
 */
copybl()
{
	register struct blk	*bp;
	register char		*chp;
	register int		extra;
	int			len;
	struct blk		**tail,
				*head;

	if (n > MAXINT)
		die(nospace);
	extra = -n;
	for (tail=&head;;) {
		len = getblk(tail);
		bp = *tail;
		tail = &bp->next;
		extra += bp->nlines;
		for (bp=head; extra > bp->nlines; bp=bp->next) {
			extra -= bp->nlines;
			fwrite(bp->blkb, sizeof *bp->blkb, BUFSIZ, stdout);
			free(bp);
		}
		head = bp;
		if (len < BUFSIZ)
			break;
	}
	for (bp=head, chp=bp->blkb; extra > 0; --extra)
		while (*chp++ != '\n')
			;
	fwrite(bp->blkb, sizeof *bp->blkb, chp-bp->blkb, stdout);
}


/*
 * Getblk allocates a blk, reads text into it and sets the nlines
 * field.  It returns the number of characters read.  It sets `bpp'
 * to point to the block.  If the block could not be allocated, then
 * it dies with the appropriate error message.
 */
getblk(bpp)
struct blk	**bpp;
{
	register struct blk	*bp;
	register int		len;

	bp = (struct blk *)malloc(sizeof *bp);
	if (bp == NULL)
		die(nospace);
	*bpp = bp;
	len = fread(bp->blkb, sizeof *bp->blkb, BUFSIZ, stdin);
	bp->nlines = cntlines(bp->blkb, len);
	return (len);
}


/*
 * Cntlines returns the number of '\n' characters in the char array
 * `chp' with length `len'.
 */
cntlines(chp, len)
register char	*chp;
int		len;
{
	register char	*limit;
	register int	res;

	for (res=0, limit=&chp[len]; chp < limit;)
		if (*chp++ == '\n')
			++res;
	return (res);
}