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cal: add -s option to specify the starting day of the week

--- a/sys/man/1/cal

+++ b/sys/man/1/cal

@@ -4,9 +4,11 @@

 .SH SYNOPSIS

 .B cal

 [

+.B -s

+.I 1..7

+] [

 .I month

-]

-[

+] [

 .I year

 ]

 .SH DESCRIPTION

@@ -29,6 +31,15 @@

 otherwise a calendar for just one month is printed.

 The calendar

 produced is that for England and her colonies.

+.PP

+.B -s

+.I N

+makes

+.I cal

+display

+.I N,

+specified as a number between 1 to 7 (Monday to Sunday), as the

+first day of the week. The default is Sunday.

 .PP

 Try

 .EX

--- a/sys/src/cmd/cal.c

+++ b/sys/src/cmd/cal.c

@@ -2,9 +2,15 @@

 #include <libc.h>

 #include <bio.h>

-char	dayw[] =

+char	*dayw[] =

 {

-	" S  M Tu  W Th  F  S"

+	" S  M Tu  W Th  F  S",

+	" M Tu  W Th  F Sa Su",

+	"Tu  W Th  F Sa Su  M",

+	" W Th  F Sa Su  M Tu",

+	"Th  F Sa Su  M Tu  W",

+	" F Sa Su  M Tu  W Th",

+	"Sa Su  M Tu  W Th  F"

 };

 char	*smon[] =

 {

@@ -21,6 +27,7 @@

 };

 char	string[432];

 Biobuf	bout;

+int	wstart;

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

 int	number(char *str);

@@ -30,21 +37,36 @@

 int	curmo(void);

 int	curyr(void);

+static void

+usage(void)

+{

+	fprint(2, "usage: cal [-s 1..7] [month] [year]\n");

+	exits("usage");

+}

+

 void

 main(int argc, char *argv[])

 {

 	int y, i, j, m;

-	if(argc > 3) {

-		fprint(2, "usage: cal [month] [year]\n");

-		exits("usage");

-	}

+	ARGBEGIN{

+	case 's':

+		wstart = atoi(EARGF(usage()));

+		if(wstart < 0 || wstart > 7)

+			usage();

+		break;

+	default:

+		usage();

+	}ARGEND

+

+	if(argc > 2)

+		usage();

 	Binit(&bout, 1, OWRITE);

 /*

  * no arg, print current month

  */

-	if(argc == 1) {

+	if(argc == 0) {

 		m = curmo();

 		y = curyr();

 		goto xshort;

@@ -55,8 +77,8 @@

  *	if looks like a month, print month

  *	else print year

  */

-	if(argc == 2) {

-		y = number(argv[1]);

+	if(argc == 1) {

+		y = number(argv[0]);

 		if(y < 0)

 			y = -y;

 		if(y >= 1 && y <= 12) {

@@ -70,10 +92,10 @@

 /*

  * two arg, month and year

  */

-	m = number(argv[1]);

+	m = number(argv[0]);

 	if(m < 0)

 		m = -m;

-	y = number(argv[2]);

+	y = number(argv[1]);

 	goto xshort;

 /*

@@ -85,17 +107,16 @@

 	if(y < 1 || y > 9999)

 		goto badarg;

 	Bprint(&bout, "   %s %ud\n", smon[m-1], y);

-	Bprint(&bout, "%s\n", dayw);

+	Bprint(&bout, "%s\n", dayw[wstart]);

 	cal(m, y, string, 24);

 	for(i=0; i<6*24; i+=24)

 		pstr(string+i, 24);

-	exits(0);

+	exits(nil);

 /*

  *	print out complete year

  */

 xlong:

-	y = number(argv[1]);

 	if(y<1 || y>9999)

 		goto badarg;

 	Bprint(&bout, "\n\n\n");

@@ -107,7 +128,7 @@

 		Bprint(&bout, "         %.3s", smon[i]);

 		Bprint(&bout, "                    %.3s", smon[i+1]);

 		Bprint(&bout, "                    %.3s\n", smon[i+2]);

-		Bprint(&bout, "%s   %s   %s\n", dayw, dayw, dayw);

+		Bprint(&bout, "%s   %s   %s\n", dayw[wstart], dayw[wstart], dayw[wstart]);

 		cal(i+1, y, string, 72);

 		cal(i+2, y, string+23, 72);

 		cal(i+3, y, string+46, 72);

@@ -115,7 +136,7 @@

 			pstr(string+j, 72);

 	}

 	Bprint(&bout, "\n\n\n");

-	exits(0);

+	exits(nil);

 badarg:

 	Bprint(&bout, "cal: bad argument\n");

@@ -232,6 +253,7 @@

 	}

 	for(i=1; i<m; i++)

 		d += mon[i];

+	d += 7 - wstart;

 	d %= 7;

 	s += 3*d;

 	for(i=1; i<=mon[m]; i++) {