# Challenge

Given that Christmas is

• December
• Month 12
• Day 25

every year: determine today's date, and whether or not today is Christmas. If it is Christmas, you must print "It's Christmas". If it is not Christmas, you must somehow wait until Christmas and then print "It's Christmas".

# Example

import time
while time.strftime("%b, %d", time.localtime()) != "Dec, 25":
time.sleep(60)
print "It's Christmas"


Python in 115 Characters

# Rules

Here are the rules:

• Assume that the computer's clock is always right.
• Your code must be able to be started at any time.
• Your code must print "It's Christmas" on Christmas.
• Looping is certainly not necessary, but once started your code should not stop until it has printed.
• Shortest code wins.
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I thought the input is in Julian date before I read this post –  SHiNKiROU Dec 21 '11 at 9:51

## Perl + Unix, 40 chars

1untildate=~/c 25/;say"It's Christmas"


This is the same as J B's Perl solution, except that I save a few chars by using the external date command instead of Perl's localtime.

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## Bash, 39

For those who just can't wait:

sudo date 12250000
echo It\'s Christmas


This follows all of the rules, especially the first one.

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+1 for abusing the rules –  FUZxxl Dec 5 '11 at 20:54
Clever. Not what I meant, but damned clever. –  pcperini Dec 5 '11 at 21:56
“...and if the computer's clock isn't always right enough, make it.” Good show! –  J B Dec 6 '11 at 8:49
You can save 5 characters if you're root. :D –  Wug Oct 8 '12 at 21:11

### Unix at: 40 chars:

echo echo "It's christmas"|at -t12252359

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+1 for pure simplicity and ingenuity. –  Polynomial Dec 12 '11 at 13:22

## PowerShell, 45 46 chars

for(;(date).date-ne'12/25'){}"It's Christmas"


It's certainly not very power-efficient, so a laptop battery might die before Christmas (reason to wish for a new one, maybe). But not sleeping is definitely shorter.

This is also locale-agnostic. And thanks to Jaykul for a nice trick in reducing this further.

## Abusing the rules a bit, 45 chars

for(){"It's Christmas"*((date)-like'12/25*')}


This will print empty lines until it's Christmas, upon which it will print “It's Christmas”.

It ...

• ... can be started at any time.
• ... prints “It's Christmas” on Christmas. Several times. The whole day long. (The rules didn't say anything about how often it may be printed.)
• ... does not print “It's Christmas” on not-Christmas (although it prints an empty line in that case; can be rectified by sacrificing another character, but then this gains nothing over the more sane solution above).
• ... does not ever stop (not even after it has printed “It's Christmas” but definitely not before).
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+1 for being locale-invariant. –  Peter Taylor Dec 5 '11 at 11:02
+1 for abusing rules –  JiminP Dec 5 '11 at 13:21
for(;(date).date-ne"12/25"){}"It's Christmas" # 45 chars –  Jaykul Dec 6 '11 at 6:32
Jaykul: Thanks ... that's something I never would have thought to be working. –  Joey Dec 6 '11 at 9:54

## Perl, 44 45

perl -E'1until localtime=~/c 25/;say"It's Christmas"'


Wouldn't GMT time be sufficient? (3 characters off ;-)

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1until localtime=~/c 25/; would save you one char. :) –  Ilmari Karonen Dec 5 '11 at 15:33
I thought I'd already tried that and it failed, but it turns out I actually forgot -E at the time. Thanks! –  J B Dec 5 '11 at 15:49
No problem. (Ps. I just posted a version of your solution using backticks instead of localtime below. Feel free to steal it if you like, but I felt the extra dependency justified a separate answer.) –  Ilmari Karonen Dec 5 '11 at 15:59
Naaaw, shame's on me for not thinking of it again. The separate answer is perfectly justified IMO (and upvoted). –  J B Dec 6 '11 at 8:54

PostScript, 90

(%Calendar%)currentdevparams begin{Month 12 eq Day 25 eq and{exit}if}loop(It's Christmas)=


Don't run on a printer, it doesn't print a page, and it will only DoS your printer until Christmas day. Then again, getting your printer back would be a nice present.

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Don't forget to tape a sign to the printer saying: DO NOT KILL JOB UNTIL CHRISTMAS! –  Joey Adams Dec 6 '11 at 16:58
I guess most printers won't even have a working hardware clock as that's an optional feature. Very nice, though :) –  Joey Dec 7 '11 at 9:38

## Perl, 45

{localtime=~/c 25/&&die"It's Christmas";redo}


## Perl, 44

using ternary operator (Thanks to Ilmari Karonen).

{localtime=~/c 25/?say"It's Christmas":redo}

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? : instead of && ; would save you one char too. (And I'd use say instead of die for prettier output.) –  Ilmari Karonen Dec 5 '11 at 15:35
@Ilmari Karonen: thanks. But by using say instead of die, the script never finish. –  M42 Dec 5 '11 at 15:43
It will, if you use the ternary operator. –  Ilmari Karonen Dec 5 '11 at 15:49
@Ilmari Karonen: yes, of course. May be i'm too tired !!! –  M42 Dec 5 '11 at 16:01

## Batch file, 68 chars

:l
@date/t|findstr/c:"-12-25">nul&&echo It's Christmas&&exit
@goto l


Not usable interactively, as it kills the session. Solving that would require 5 more characters.

Also locale-sensitive. This works on my locale which uses ISO 8601 date format.

But hey, it's a batch file (by most not even regarded as a programming language). And shorter than Javascript (and on par with Python).

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## Ruby, 53

until Time.now.to_s=~/c 05/
end
puts"It's Christmas!"

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## Javascript, 51 chars

It's a CPU killer:

while(!/c 25/.test(Date()));alert("It's Christmas")

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I wanted to do this without parsing strings. Subsequently, there's a lot of magic numbers in my code.

I did some approximation to account for leap years. No one said that it had to print it out right on 00:00:00, Dec. 25!

## Perl, 8069 57 characters

{(time-30931200)%31557600<86399?die"It's Christmas":redo}


Edited for more concise looping!

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## Mathematica, 47

While[Date[][[2;;3]]!={12,25}];"It's Christmas"

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## (pdf)eTeX - 180 chars only December 1-25.

\lccodem~\let\e\expandafter\def~{\ifdim900pt<\pdfelapsedtime
sp\pdfresettimer\else\e~\fi}\lowercase\e{\e\scantokens\e
{\romannumeral\numexpr (25 - \day)*96000}}It's Christmas!\bye


TeX only has a way to access the date when the program starts, and the time elapsed since the start, capped at 32768 seconds, so I need to compute the number of seconds to wait, and for each second do a loop which waits for the elapsed time to reach 1s and reset the time. (Precisely, I'm doing blocks of 900 seconds.)

Working for any month requires more work: 355 chars.

\lccodem=~\let\o\or\let\y\year\let\n\numexpr\let\e\expandafter
\def\b#1{\ifnum#1=\n(#1/4)*4\relax+1\fi}\def~{\ifdim
900pt<\pdfelapsedtime sp\pdfresettimer\else\e~\fi}\lowercase
\e{\e\scantokens\e{\romannumeral\n(25-\day+\ifcase\month\o334\b\y
\o303\b\y\o275\o244\o214\o183\o153\o122\o91\o61\o30\o0\ifnum25<\day
365\b{\n\y+1}\fi\fi)*96000}}It's Christmas!\bye

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## Javascript, 938978 77 chars

function x(){Date().match("c 25")?alert("It's Christmas"):setTimeout(x,1)}x()

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@Joey Thanks! I forgot about that. –  JiminP Dec 5 '11 at 9:52
Another non-blocking version: setInterval('/c 25/.test(Date())&&alert("It\'s Christmas")',9) at 61 chars ... the only drawback is that it will alert() all day on Christmas. –  David Murdoch Dec 6 '11 at 3:14

## D, 130

import std.datetime,std.stdio;
main(){
do{
auto t = Clock.currTime();
}while(t.month!=12||t.day!=25);
writeln("It's Christmas");
}

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You can probably save two characters in the assignment. And a few more by reducing the number of lines. –  Joey Dec 5 '11 at 16:28
I can also save some by using t.month^12|t.day^25 (if I get my priorities right) –  ratchet freak Dec 5 '11 at 18:38

## Python, 68

import time
while'c 25'not in time.asctime():1
print"It's Christmas"

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# Groovy, 55

while(!new Date()==~/.*c 25.*/);
println"It's Christmas"


Think it works, but still waiting for output.

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If Groovy's regexps are anything like in most other languages, those .* are entirely unnecessary. (Ps. You can test it by waiting for Dec 5 instead of 25.) –  Ilmari Karonen Dec 5 '11 at 18:54
Ilmari, Groovy is a JVM language and Java's regexes are anchored by default. –  Joey Dec 5 '11 at 19:19
Ilmari, I'd check but my program is still running –  Alison Dec 6 '11 at 16:56

## Q, 63 chars

system"t 1000";.z.ts:{$["12.25"~-5#-3!.z.d;1"It's Christmas";]}  will work for christmas day on every year - add comment # Groovy - 88 new Timer().schedule({print"It's Christmas"}as TimerTask,Date.parse("yyddMM","112512"))  - Is all that whitespace necessary? – Joey Dec 5 '11 at 16:28 @Joey no, it was for the sake of readability. – mohammad shamsi Dec 5 '11 at 16:32 Does it work every year? Don't think so. – user unknown Dec 8 '11 at 22:43 add comment ### bash-n-date: 69 chars: sleep$(($(date -d"12/25" +%s)-$(date +%s))) && echo "It's X-Ray    "


But it will fail on Dec. 26th to Dec. 31th.

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## MySQL, 180 chars

Because what are you using your database engine for, anyway?

DELIMITER $$CREATE FUNCTION c() RETURNS CHAR(14) BEGIN a: LOOP IF DAY(NOW())=25 && MONTH(NOW())=12 THEN RETURN 'It\'s Christmas'; END IF; END LOOP a; END$$
DELIMITER ;
SELECT c();


Not very competitive lengthwise, but hey, it's doable!

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 system"t 1000";.z.ts:{if[.z.d~2012.12.25;1"It’s Christmas"]}