2003.07_Cal and Date-Create Calendars and Reminder Utilities.pdf

LINUX USER

date & cal

Time for a date

The command line tools cal and date

play June 1999, but June in the year 99

AD – cal goes back to January 1 0001.

The -j option tells cal to output the

number of days since the beginning of

the year ( Julian representation):

ing of percent signs, “%”, and letters

indicating various format options. Table

1 provides an overview of the most

important output formats.

You can specify -d DATE (or --

date=DATE ) to use the supplied DATE .

Values such as yesterday , next , 3 days

ago or the full date ( 09 June 1973 ) are

possible:

are used to create calendars and edit

dates and times. Used smartly, you

can even create your own birthday

huhn@asteroid:~$ cal -j

April 2003

SMuWhFS

91 92 93 94 95

reminder utility. BY HEIKE JURZIK

I t does not always have to be a GUI

[...]

huhn@asteroid:~$ date -d U

"09 June 1973"

Sat Jun 9 00:00:00 CET 1973

tool or a PDA interface that helps you

keep track of your appointments.

Linux’ cal and date functions can help

you create your very own command line

based calendar software. These tools are

still the undisputed champions when it

comes to shell scripts. After taking a

short look at the various cal and date

options, we will be moving on to a sim-

ple example that explains how a few

easy steps can create a script that

reminds you of your loved ones’ birth-

days when you log on to Linux.

The Right Time

The date command tells you the current

date and time (for your timezone). The

superuser root is additionally permitted

to set the system time. Without any para-

meters date simply outputs the current

system date and time:

Up to date!

The superuser root can use the date com-

mand to set the system date and time.

The command expects a date/time value

in MMDDhhmmCCYY.ss format, without

a preceding plus character + , such as:

huhn@asteroid:~$ date

Wed Apr 23 12:55:37 CEST 2003

asteroid:~# date 04111723

Fri Apr 11 17:23:00 CEST 2003

If you want to change the English expres-

sions for weeks and months, you can set

the LC_TIME environment variable to a

valid Locale . export LC_TIME=de_DE

tells the date command to speak Ger-

man, for example:

The following values can be set:

• MM: Month, e.g. 04

• DD: Day, e.g. 13

• hh: Hour, e.g. 12

• mm: Minute, e.g. 59

• CC: the first two digits of the year

(optional), e.g. 19

•YY: the second two digits of the year

(optional), e.g. 73

• ss: seconds (optional), e.g. 24

An additional -s parameter allows a

slightly less strict notation when specify-

ing the time e.g. date -s 04/29/2003 :

What Year?

This simple program displays a basic cal-

endar in the command line:

huhn@asteroid:~$ cal

April 2003

Su Mo Tu We Th Fr Sa

12345

6789012

13 14 15 16 17 18 19

20 21 22 23 24 25 26

27 28 29 30

huhn@asteroid:~$ export LC_ U

TIME=de_DE

huhn@asteroid:~$ date

Mit Apr 23 13:55:32 CEST 2003

Environment variables can also be used

to tell date to produce different output.

The directory /usr/share/zoneinfo con-

tains an overview of the timezones,

some of which are in subdirectories. You

can temporarily change the TZ (for

“TimeZone”) variable to discover the

time on say Easter Island:

Executing the command without any

flags will simply display the calendar for

the current month. However, the -y

option outputs a calendar for the current

year. Pipe the output through less ( cal -y

| less ), to prevent the output from

scrolling off screen. cal will display a

specific month, if you additionally sup-

ply the month and year (four digits), as

in cal 06 2003 for June 2003. Don’t make

the mistake of supplying a two-digit year

format; entering cal 06 99 would not dis-

asteroid:~# date -s 04/29/2003

Tue Apr 29 00:00:00 CEST 2003

asteroid:~# date -s "04/29/ U

2003 15:58"

Tue Apr 29 15:58:00 CEST 2003

huhn@asteroid:~$ TZ=Chile/ U

EasterIsland date

Mit Apr 23 11:34:26 EAST 2003

Note that changing the system time does

not affect the CMOS clock. To adjust the

CMOS clock to the current system time,

you again need to log in as the superuser

root and call hwclock -w (or the longer

version hwclock --systohc , the option

means “system to hardware clock”).

You can also assign different output for-

mats to the date. To do so, use a plus

sign, “+”, followed by a string consist-

July 2003

www.linux-magazine.com

Command Line: date & cal

date & cal

LINUX USER

Table 1: Output Formats for date

Listing 1: The Birthday Script

The per cent character itself

#!/bin/sh

End of line

Ta b

today_cal=`date +%e`

echo -e "`cal | sed s/"${today_ U

cal}\>"/\\\\\\\\e[31\;7m\&\\\\\\\\e[39\;0m/g`"

echo

today=`date +%d.%m`

echo Today's date $today, birthday$s$:

echo -e "\033[31m"; grep "^$today" U

~/.birthdays; echo -e "\033[0m"

nextday=`date -d tomorrow +%d.%m`

echo Tomorrow is $nextday, birthday$s$:

grep "^$nextday" ~/.birthdays

echo

this_month=`date +%m`

echo In `date +%B` the following people U

will be celebrating their birthdays:

egrep "^[0-9]*\.$this_month\." ~/.birthdays

Weekday (short form), Output: Mon

Weekday (long form), Output: Monday

Name of month (short form), Output: Apr

Name of month (long form), Output: April

Day (two digits), Output: 01

Day (blank padded), Output: 1

Date in format mm/dd/yy , Output: 04/29/03

Hours (0 - 23)

Hours (1 - 12)

Minutes (00 - 59)

am/pm, (AM, PM)

Time, twelve hour clock (hh:mm:ss AM/PM)

Time, 24 hour clock (hh:mm:ss)

Timezone

Happy Birthday to you!

The date command is really useful in

shell scripts. The birthday diary (see

Listing 1) shows how to use a neat com-

bination of cal and date , based on a

hidden file called ~/.birthdays in your

own home directory. The file has a date

and a name in each line:

output from date +%e and a word end

( > is the regex for this). This is replaced

by an ESC[31;7m (an ANSI escape

sequence that switches the terminal

to inverted red output), the selection

itself ( & is the sed reference to the

replaced string) and ESC[39;0m (a

second sequence that restores the

standard terminal output mode). The

numerous backslashes are required to

mask these expressions for the shell

and sed .

Following this, the output from date

+%d.%m is assigned to the today

variable. The script first outputs today’s

date, then switches the terminal to red

(ANSI sequence). grep searches the

~/.birthdays file for lines starting with

”^$today” . Finally, the normal terminal

output mode is restored.

The last line of the script can be

interpreted as follows: the egrep program

(a grep variant that can handle regular

expressions) searches ~/.birthdays for

lines that start with any number of

numbers (0 - 9), followed by a period,

the current month and another period.

The “^” character means “at the start of

a line” and “[0-9]*” indicates any

number of characters between 0 and 9.

An entry in the following format

. ~/birthday.sh

huhn@asteroid:~$ cat .birthdays

28.02. Petronella

28.04. Jones

27.04. Easter

...

in the .profile will run the script each

time you log on – and that should help

you keep an eye on those important

dates.

The birthday.sh script first assigns the

output from date +%e to the today_cal

variable (see also Table 1). The echo -e

command that follows, enables the use

of escape sequences, including the new-

line character, \n , and the tab \t . The cal

command outputs the calendar and this

output is piped (“|”) to sed . sed then

searches the calendar for the section

containing the day specified by the

Heike Jurzik studied

German, Computer

Science and English at

the University of

Cologne, Germany.

She discovered Linux

in 1996 and has been fascinated with

the scope of the Linux command line

ever since. In her leisure time you

might find Heike hanging out at Irish

folk sessions or visiting Ireland.

GLOSSARY

Julian / Gregorian calendar: The Julian calen-

dar, a major reform of the Roman calendar,

was introduced by Julius Caesar in the year 46

BC, adding an extra day every four years.

These became known as leap years. The

beginning of the year was moved to January

1. As this calendar did not precisely reflect

astronomical time, Pope Gregory XIII intro-

duced a reformed calendar in the year 1582

(ten days were dropped to compensate the

calendar, and a new leap year format that

dropped the extra day in leap years divisible

by 100 by not by 400 was introduced). The

Gregorian calendar was originally only intro-

duced in Catholic countries, but gradually the

new calendar did assert itself.

Locales: Linux supports a variety of output

languages for program and system messages,

dates or currency values. The locale com-

mand,“locale -a”, will tell you the names of

the locales installed on your system.

CMOS : C omplimentary M etal- O xide S emi-

conductor. Nearly all PCs have a battery

driven clock that increments the date and

time when the computer is powered off. As

the clock is embedded in the same chip that

has the CMOS RAM, it is referred to as a CMOS

clock, or by one of the following common

names: hardware clock, RTC (Real Time Clock)

or BIOS clock.

www.linux-magazine.com

July 2003

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: