WHEN(1) General Commands Manual WHEN(1)

when — date calculator

when [expr]

when -

when is a date calculator. If no expr is given, expressions are read from standard input. If - is given, the intervals between each named date and today are printed.

The grammar is as follows:

Today's date. The empty expression is equivalent.
name [ date]
A named date. Names are alphanumeric including underscores.
month date [year]
A full date, or a date in the current year. Months can be abbreviated to three letters.
day
A day of the week in the current week. Days can be abbreviated to three letters.
date
The date one week before.
date
The date one week after.
date interval
The date after some interval.
date - interval
The date before some interval.
date - date
The interval between two dates.
num
A number of days.
num
A number of weeks.
num
A number of months.
num
A number of years.

The file $XDG_CONFIG_HOME/when/dates or ~/.config/when/dates is read before any other expressions, if it exists.

How long until Christmas.
The date next Friday.
. + 2w
Your last day at work.

Checking a milestone:

$ echo 'hrt = oct 15 2021' >> ~/.config/when/dates
$ when -hrt
September 19, 2022 OpenBSD 7.3

when.y in git 

/* Copyright (C) 2019, 2022  June McEnroe <june@causal.agency>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

%{

#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <sysexits.h>
#include <time.h>

static void yyerror(const char *str);
static int yylex(void);

#define YYSTYPE struct tm

static const char *Days[7] = {
	"Sunday", "Monday", "Tuesday", "Wednesday",
	"Thursday", "Friday", "Saturday",
};

static const char *Months[12] = {
	"January", "February", "March", "April", "May", "June",
	"July", "August", "September", "October", "November", "December",
};

static const struct tm Week = { .tm_mday = 7 };

static struct tm normalize(struct tm date) {
	time_t time = timegm(&date);
	struct tm *norm = gmtime(&time);
	if (!norm) err(EX_OSERR, "gmtime");
	return *norm;
}

static struct tm today(void) {
	time_t now = time(NULL);
	struct tm *local = localtime(&now);
	if (!local) err(EX_OSERR, "localtime");
	struct tm date = {
		.tm_year = local->tm_year,
		.tm_mon = local->tm_mon,
		.tm_mday = local->tm_mday,
	};
	return normalize(date);
}

static struct tm monthDay(int month, int day) {
	struct tm date = today();
	date.tm_mon = month;
	date.tm_mday = day;
	return normalize(date);
}

static struct tm monthDayYear(int month, int day, int year) {
	struct tm date = today();
	date.tm_mon = month;
	date.tm_mday = day;
	date.tm_year = year - 1900;
	return normalize(date);
}

static struct tm weekDay(int day) {
	struct tm date = today();
	date.tm_mday += day - date.tm_wday;
	return normalize(date);
}

static struct tm scalarAdd(struct tm a, struct tm b) {
	a.tm_mday += b.tm_mday;
	a.tm_mon += b.tm_mon;
	a.tm_year += b.tm_year;
	return a;
}

static struct tm scalarSub(struct tm a, struct tm b) {
	a.tm_mday -= b.tm_mday;
	a.tm_mon -= b.tm_mon;
	a.tm_year -= b.tm_year;
	return a;
}

static struct tm dateAdd(struct tm date, struct tm scalar) {
	return normalize(scalarAdd(date, scalar));
}

static struct tm dateSub(struct tm date, struct tm scalar) {
	return normalize(scalarSub(date, scalar));
}

static struct tm dateDiff(struct tm a, struct tm b) {
	time_t atime = timegm(&a), btime = timegm(&b);
	if (atime < btime) {
		struct tm x = a;
		a = b;
		b = x;
		time_t xtime = atime;
		atime = btime;
		btime = xtime;
	}
	struct tm diff = {
		.tm_year = a.tm_year - b.tm_year,
		.tm_mon = a.tm_mon - b.tm_mon,
		.tm_mday = a.tm_mday - b.tm_mday,
	};
	if (
		a.tm_mon < b.tm_mon ||
		(a.tm_mon == b.tm_mon && a.tm_mday < b.tm_mday)
	) {
		diff.tm_year--;
		diff.tm_mon += 12;
	}
	if (a.tm_mday < b.tm_mday) {
		diff.tm_mon--;
		diff.tm_mday = 0;
		while (dateAdd(b, diff).tm_mday != a.tm_mday) diff.tm_mday++;
	}
	diff.tm_yday = (atime - btime) / 24 / 60 / 60;
	return diff;
}

static struct {
	size_t cap, len;
	struct tm *ptr;
} dates;

static struct tm getDate(const char *name) {
	for (size_t i = 0; i < dates.len; ++i) {
		if (!strcmp(dates.ptr[i].tm_zone, name)) return dates.ptr[i];
	}
	return (struct tm) {0};
}

static void setDate(const char *name, struct tm date) {
	for (size_t i = 0; i < dates.len; ++i) {
		if (strcmp(dates.ptr[i].tm_zone, name)) continue;
		char *tm_zone = dates.ptr[i].tm_zone;
		dates.ptr[i] = date;
		dates.ptr[i].tm_zone = tm_zone;
		return;
	}
	if (dates.len == dates.cap) {
		dates.cap = (dates.cap ? dates.cap * 2 : 8);
		dates.ptr = realloc(dates.ptr, sizeof(*dates.ptr) * dates.cap);
		if (!dates.ptr) err(EX_OSERR, "realloc");
	}
	dates.ptr[dates.len] = date;
	dates.ptr[dates.len].tm_zone = strdup(name);
	if (!dates.ptr[dates.len].tm_zone) err(EX_OSERR, "strdup");
	dates.len++;
}

static bool silent;

static void printDate(struct tm date) {
	if (silent) return;
	printf(
		"%.3s %.3s %d %d\n",
		Days[date.tm_wday], Months[date.tm_mon],
		date.tm_mday, 1900 + date.tm_year
	);
}

static void printScalar(struct tm scalar) {
	if (silent) return;
	if (scalar.tm_year) printf("%dy ", scalar.tm_year);
	if (scalar.tm_mon) printf("%dm ", scalar.tm_mon);
	if (scalar.tm_mday % 7) {
		printf("%dd ", scalar.tm_mday);
	} else if (scalar.tm_mday) {
		printf("%dw ", scalar.tm_mday / 7);
	}
	if (scalar.tm_yday && scalar.tm_mon) {
		if (scalar.tm_yday >= 7) {
			printf("(%dw", scalar.tm_yday / 7);
			if (scalar.tm_yday % 7) {
				printf(" %dd", scalar.tm_yday % 7);
			}
			printf(") ");
		}
		printf("(%dd) ", scalar.tm_yday);
	}
	printf("\n");
}

%}

%token Name Number Month Day
%left '+' '-'
%right '=' '<' '>'

%%

expr:
	date { printDate($1); }
	| scalar { printScalar($1); }
	;

date:
	dateLit
	| Name { $$ = getDate($1.tm_zone); free($1.tm_zone); }
	| Name '=' date { setDate($1.tm_zone, $3); free($1.tm_zone); $$ = $3; }
	| '(' date ')' { $$ = $2; }
	| '<' date { $$ = dateSub($2, Week); }
	| '>' date { $$ = dateAdd($2, Week); }
	| date '+' scalar { $$ = dateAdd($1, $3); }
	| date '-' scalar { $$ = dateSub($1, $3); }
	;

scalar:
	scalarLit
	| '(' scalar ')' { $$ = $2; }
	| scalar '+' scalar { $$ = scalarAdd($1, $3); }
	| scalar '-' scalar { $$ = scalarSub($1, $3); }
	| date '-' date { $$ = dateDiff($1, $3); }
	;

dateLit:
	{ $$ = today(); }
	| '.' { $$ = today(); }
	| Month Number { $$ = monthDay($1.tm_mon, $2.tm_sec); }
	| Month Number Number { $$ = monthDayYear($1.tm_mon, $2.tm_sec, $3.tm_sec); }
	| Day { $$ = weekDay($1.tm_wday); }
	;

scalarLit:
	Number 'd' { $$ = (struct tm) { .tm_mday = $1.tm_sec }; }
	| Number 'w' { $$ = (struct tm) { .tm_mday = 7 * $1.tm_sec }; }
	| Number 'm' { $$ = (struct tm) { .tm_mon = $1.tm_sec }; }
	| Number 'y' { $$ = (struct tm) { .tm_year = $1.tm_sec }; }
	;

%%

static void yyerror(const char *str) {
	warnx("%s", str);
}

static const char *input;

static int yylex(void) {
	while (isspace(*input)) input++;
	if (!*input) return EOF;

	if (isdigit(*input)) {
		char *rest;
		yylval.tm_sec = strtol(input, &rest, 10);
		input = rest;
		return Number;
	}

	size_t len;
	for (len = 0; isalnum(input[len]) || input[len] == '_'; ++len);

	if (len >= 3) {
		for (int i = 0; i < 7; ++i) {
			if (strncasecmp(input, Days[i], len)) continue;
			yylval.tm_wday = i;
			input += len;
			return Day;
		}

		for (int i = 0; i < 12; ++i) {
			if (strncasecmp(input, Months[i], len)) continue;
			yylval.tm_mon = i;
			input += len;
			return Month;
		}
	}

	if (len && (len != 1 || !strchr("dwmy", *input))) {
		yylval.tm_zone = strndup(input, len);
		if (!yylval.tm_zone) err(EX_OSERR, "strndup");
		input += len;
		return Name;
	}

	return *input++;
}

int main(int argc, char *argv[]) {
	size_t cap = 0;
	char *line = NULL;

	char path[PATH_MAX];
	const char *configHome = getenv("XDG_CONFIG_HOME");
	if (configHome) {
		snprintf(path, sizeof(path), "%s/when/dates", configHome);
	} else {
		snprintf(path, sizeof(path), "%s/.config/when/dates", getenv("HOME"));
	}

	FILE *file = fopen(path, "r");
	if (file) {
		silent = true;
		while (0 < getline(&line, &cap, file)) {
			input = line;
			yyparse();
		}
		fclose(file);
		silent = false;
	} else if (errno != ENOENT) {
		err(EX_CONFIG, "%s", path);
	}

	if (argc > 1) {
		if (strcmp(argv[1], "-")) {
			input = argv[1];
			return yyparse();
		} else {
			for (size_t i = 0; i < dates.len; ++i) {
				printf("%s: ", dates.ptr[i].tm_zone);
				printScalar(dateDiff(today(), dates.ptr[i]));
			}
			return EX_OK;
		}
	}

	struct tm date = today();
	printDate(date);
	printf("\n");

	while (0 < getline(&line, &cap, stdin)) {
		if (line[0] == '\n') continue;

		if (today().tm_mday != date.tm_mday) {
			warnx("the date has changed");
			date = today();
		}

		input = line;
		yyparse();
		printf("\n");
	}
}