Ihre Aufgabe ist es, ein Programm zu erstellen, das "Greetings, Planet!" genau auf die Konsole. Scheint einfach genug, oder? Nun, hier ist der Trick. Der Code muss ein Palindrom sein, dh er liest von rechts nach links genauso wie von links nach rechts. Standardlücken sind NICHT erlaubt.

///, 37 bytes

Greetings, Planet!/!tenalP ,sgniteerG

TI-BASIC, 67 bytes

"!tenalP ,sgniteerG"
"Greetings, Planet!"

This works because the last line of a program is displayed on the screen, while the first string is essentially treated as a comment.

Each lowercase letter is stored as 2 bytes, and the remaining characters are 1 byte. If I were to bend the rules and print in all caps, it would be 41 bytes:

"!TENALP ,SGNITEERG"
"GREETINGS, PLANET!"

I know this is a bit late (and a bit finicky), but...

><> (Fish), 47 45 47 Bytes (really 43 45, if I wasn't using the randomized direction)

x"!tenalP ,sgniteerG"!|o|!"Greetings, Planet!"x

These answers are a bit different to every other; there is a chance for either direction of code to be executed.

So, by "printing to console", I assumed you meant printing to stdout. This throws an error; the error is thrown to stderr AFTER the string is printed to stdout.

To prove that this worked both ways, I used the "random direction" director, "x". Fish is a two-dimensional language, so, no matter which way the director points, the code will still (eventually) be executed.

Assuming that the first director points to the right, the characters are loaded to the "stack" in reverse order, then the reverse of the reverse (or the normal text) is printed.

Assuming that both directors point to the left, the characters are, once again, loaded to the "stack" in reverse order (because the code loads it in backwards here, direction is to the left), then the reverse of the reverse (or the normal text) is printed.

If the randomized director points up or down, this won't matter - fish knows to loop to the underside or overside of the code, pointing back to the randomizer. In this way, it will continue to loop with the randomizers until it points inward, towards the code to execute.

The !|o|! bit does the following, from both sides:

• ! skips the next instruction (will always skip |)

• | is a reflector; it points inward back towards o.

• o outputs the current item of the stack to console as a character and removes it from the stack.

So, essentially, this is the "two mirrors in a bathroom pressed up together" trick, where I output until I can't anymore.

Now using a cat emoji. >o< redirects the output inward infinitely, still throwing the error, but I can get away with not using a skip into reflection.

Turns out I was right the first time - the second attempt was not palindromic, but it was reflective.

Fish (without printing to stderr), 64 Bytes (ew)

x"!tenalP ,sgniteerG"!;oooooooooooooooooo;!"Greetings, Planet!"x

This dude's a little longer.

It has the same randomized arrow function (to prove it works both ways) and does not print to stderr.

The difference here is obvious; I literally print out every item in the stack, then end execution with ;.

The !; does not end execution immediately, as ! skips the next item (end exec, in this case) and continues until it hits the other side, which acts as ;!, wherein it ends execution before it skips anything.

It follows the same randomized direction pattern as the shorter answer.

Bubblegum, 38 bytes

0000000: 73 2f 4a 4d 2d c9 cc 4b 2f d6 51 08 c8 49 cc 4b 2d 51 04  s/JM-..K/.Q..I.K-Q.
0000013: 04 51 2d 4b cc 49 c8 08 51 d6 2f 4b cc c9 2d 4d 4a 2f 73  .Q-K.I..Q./K..-MJ/s

Macaroni 0.0.2, 52 bytes

print "Greetings, Planet!""!tenalP ,sgniteerG" tnirp

A solution that doesn't use comments. (Mostly because Macaroni doesn't have comments...)

CJam, 41 bytes

Thanks to Dennis for the three bytes off.

"!tenalP ,sgniteerG";"Greetings, Planet!"

Foo, 39 bytes

"Greetings, Planet!"!tenalP ,sgniteerG"

Try it online.

JavaScript, 56 bytes

This can run in any browser.

alert("Greetings, Planet!")//)"!tenalP ,sgniteerG"(trela

GolfScript, 41 bytes

"Greetings, Planet!":"!tenalP ,sgniteerG"

Look ma, no no-ops! Try it online in Web GolfScript.

The second half of the source code stores the string in the second string.

"Greetings, Planet!":"!tenalP ,sgniteerG"
"!tenalP ,sgniteerG"

would print

Greetings, Planet!Greetings, Planet!

C++, 129 bytes

Trying to do this without comments led me into a deep, dark preprocessor nightmare with no way out that I could see. Instead I've just aimed to get it as short as possible.

/**/
#include<cstdio>
int main(){puts("Greetings Planet!");}//*/
/*//};)"!tenalP sgniteerG"(stup{)(niam tni
>oidtsc<edulcni#
/**/

Python 3, 57 bytes

print('Greetings, Planet!')#)'!tenalP ,sgniteerG'(tnirp

I fixed the issue with parenthesis.

Python 2, 53 bytes

print'Greetings, Planet!'#'!tenalP ,sgniteerG'tnirp

I used advantage of the lack of required parenthesis and spaces in Python 2, but there wasn't that big of a difference.

Jelly, non-competing

25 bytes This answer is non-competing, since the challenge predates the creation of Jelly.

»1ị“RsẈḄ,#ʠU“Uʠ#,ḄẈsR“ị1»

Look 'ma, no comments! Try it online!

How it works

»1ị“RsẈḄ,#ʠU“Uʠ#,ḄẈsR“ị1»  Main link. No arguments.

   “        “        “  »  Decompress all three strings; yield a list of strings.
    RsẈḄ,#ʠU               (decompresses to 'Greetings, Planet!')
             Uʠ#,ḄẈsR      (decompresses to ' WafdkmC Posited,')
                      ị1   (decompresses to 'Taarhus')

»1                         Take the maximum of the default argument (0) and 1.
  ị                        Select the string at the index to the left.

Stuck, 41 Bytes

"Greetings, Planet!"p"!tenalP ,sgniteerG"

Fairly similar to the CJam answer, except in Stuck if a print command is issued, automatic stack printing is suppressed.

Mathematica, 52 bytes

Print@"Greetings, Planet!""!tenalP ,sgniteerG"@tnirP

Also generates a Null "!tenalP ,sgniteerG"[tnirP] which doesn't get printed.

Fission, 45 43 bytes

Thanks to jimmy23013 for saving 2 bytes.

;"!tenalP ,sgniteerG"R"Greetings, Planet!";

Try it online!

R initialises an atom which moves to the right. " toggles string mode which simply prints the desired string to STDOUT before hitting ;, which destroys the atom and terminates the program. The first half is simply never executed.

05AB1E, 16 bytes

Code:

”!º¥,ÁÙ””ÙÁ,¥º!”

Explanation:

”!º¥,ÁÙ”          # Compressed string which results in "! Crm, Everywhere".
        ”ÙÁ,¥º!”  # Compressed string which results in "Greetings, Planet!".
                  # Top of stack is implicitly outputted.

Try it online!

STATA, 52 bytes

di "Greetings, Planet!"//"!tenalP ,sgniteerG" id

A slightly longer (53 byte) version that doesn't use comments is:

#d
di "Greetings, Planet!";"!tenalP ,sgniteerG" id
d#

#d [something] changes the delimiter (initially a carriage return) to ; unless [something] is cr, so the first command changes the delimiter to ;, the second prints the string, and the third (which continues until the end) is apparently a nop, though I have no idea why. I would have guessed that this would throw an error (unrecognized command "!tenalP ,sgniteerG" or something), but apparently not.

Japt, 29 bytes

^{This programming language was made after the question was posted, but was not made for this question.}

`!t?ÓP ,?Ä>ÎG`;`GÎ>Ä?, PÓ?t!`

Try it online!

Each ? is an unprintable Unicode char: U+0082, U+000F, U+000F, and U+0082, respectively.

Fun fact: If Japt had been published a month sooner, it would have legitimately won this challenge.

APL, 41 bytes

'Greetings, Planet!'⍝'!tenalP ,sgniteerG'

In APL, the last value is printed and the lamp character (⍝) start a comment.

GolfScript, 41 bytes

"Greetings, Planet!"#"!tenalP ,sgniteerG"

Try it online !

TCL, 80 Bytes

proc unknown args {puts "Hello World!"}
}"!dlroW olleH" stup{ sgra nwonknu corp

explanation: TCL executes a global proc unknown when it encounters a call to an undefined command, the first line redefines that proc to a simple "hello world" program.

TCL's quoting rules are quite subtle, an open brace starts a quoted word that extends to the next matching close brace, allowing nested, quoted words. Braces are otherwise treated as normal characters. five words: }"!dlroW olleH", stup{, sgra, nwonknu and corp. No command named }"!dlroW olleH" has been defined, so the undefined proc from the first line is invoked instead.

A similar question was posted on the StackOverflow of antiquity; which has since been closed and deleted. I used my solution as a tongue in cheek TCL sample in this answer, and am now getting comments asking for an explanation, so I recreate my answer here.

Keg, 41 bytes

Greetings\, Planet\!#!\tenalP ,\sgniteerG

Try it online!

Vitsy, 41 Bytes

_{This programming language was made after the question was posted, but was not made for this question.}

"!tenalP ,sgniteerG"Z"Greetings, Planet!"

The Z character outputs everything in the stack to STDOUT.

Try it online!

Unefunge 98 - 49 bytes

"!tenalP ,sgniteerG<DC1>"k,@,k"<DC1>Greetings, Planet!"

The code above contains two unprintable characters with code 17 (device control 1) represented by <DC1>.

MSM, 73 bytes

GGreetings, Planet!.................,.................!tenalP ,sgniteerGG

The first half just before the middle , builds a reverse greeting string including the additional G on the very right. The middle , drops it and the rest is a canonical "Hello/Greeting/whatever" program. The additional characters on both ends are needed, because the message contains a ,. The left one is executed and drops the s. Both , and s need a replacement for the left concatenation dots, hence the Gs. The , on the right isn't executed, but build into the final string.

CoffeeScript, 53 bytes

Similar to Ruby and Lua and pretty much all the variants here.

alert 'Greetings, Planet!'#'!tenalP ,sgniteerG' trela

Ruby, 43 bytes

p"Greetings, Planet!"#"!tenalP ,sgniteerG"p

Bash, 52 48 bytes

echo Greetings, Planet!||!tenalP ,sgniteerG ohce

Also works in ksh, zsh, yash, dash. But not tcsh.

$ cat x.sh
echo Greetings, Planet!||!tenalP ,sgniteerG ohce
$ bash x.sh
Greetings, Planet!
$ ksh x.sh
Greetings, Planet!
$ zsh x.sh
Greetings, Planet!
$ yash x.sh
Greetings, Planet!
$ dash x.sh
Greetings, Planet!
$ tcsh x.sh
tenalP: Event not found.
$

Lua, 52 Bytes

print"Greetings, Planet!"--"!tenalP ,sgniteerG"tnirp

In Lua terminal, it is only 44 bytes with

="Greetings, Planet!"--"!tenalP ,sgniteerG"=

Milky Way 1.5.10, 43 41 39 bytes

"Greetings, Planet!"!tenalP ,sgniteerG"

Explanation

"Greetings, Planet!"                       # push the string to the stack
                    !                      # output the TOS
                     tenalP ,sgniteerG"    # throws an error and exits

Usage

python3 milkyway.py <path-to-code>