Programming Puzzles & Code Golf Stack Exchange is a question and answer site for programming puzzle enthusiasts and code golfers. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

This challenge is pretty simple. As input, you take in a regular expression.

Then, you output a truthy/falsey of whether or not your source code matches the regular expression. It's that simple! Just two more things:

  • No quine builtins; you may, however, access the code's source code by file IO, etc.
  • This is , so shortest code in bytes wins!


If your source code was say, abc, an input of a\wc would return true and an input of a\dc would return false.

share|improve this question
Example please? – Mama Fun Roll Jan 12 at 2:29
@CᴏɴᴏʀO'Bʀɪᴇɴ no, that's fine. – Maltysen Jan 12 at 2:31
1. I don't think just a BRE with simple character classes is specific enough. What BRE features have to be supported? 2. \d is not special in BRE; it matches the character d. 3. Choosing a specific regex flavor restricts your challenge to languages that support it, and few languages support BRE. Is that intentional? – Dennis Jan 12 at 2:33
I'd recommend leaving it up to the answerer. If language x uses regex flavor y by default, let it use that flavor in this challenge. – Dennis Jan 12 at 2:36
@Maltysen Why don't you add a substring example to the question body? – feersum Jan 12 at 3:10

Z shell, 12 bytes

grep "$@"<$0

Zsh conditionals understand only exit codes, and the scripts exits with 0 or 1 accordingly.

In addition, this prints a non-empty string (the source code) for a match and an empty one for a mismatch, which could be as truthy/falsy values in combination with test/[.

The program reads its own file, but according to this comment by the OP, this is allowed.

share|improve this answer
Aaand Dennis won. ¯\_(ツ)_/¯ – Cᴏɴᴏʀ O'Bʀɪᴇɴ Jan 12 at 2:43
This doesn't work. It breaks on patterns with spaces in them. – feersum Jan 12 at 2:51
@feersum Whoops! Thanks for pointing that out. I have edited my answer. – Dennis Jan 12 at 2:53
Now it breaks if it is written to a file with spaces in the name. Or a file called -v. Or... – Ben Millwood Jan 12 at 15:08
@BenMillwood I'd normally say don't save it with such a file name, but switching to zsh makes it bullet proof without incrementing the byte count. – Dennis Jan 12 at 15:24

JavaScript (ES6), 39

share|improve this answer
Just about to post this, but you beat me to it. Great job! – Mama Fun Roll Jan 12 at 3:29
The beginning of your code looks like me when trying to understand this : (f=_=) – Nico Jan 12 at 9:35

Python 3, 119 bytes

This just looks cooler, IMO (and it doesn't read the file).

(lambda i:print(bool(__import__('re').search(input(),i))))("(lambda i:print(bool(__import__('re').search(input(),i))))")

Python 3, 67 bytes


Added after reading this comment.

share|improve this answer
int is shorter than bool. – cat Mar 10 at 22:42

Julia, 64 54 bytes


Julia regular expressions use PCRE. While reading the source code of the file is a standard loophole for quines, in this case it has been explicitly allowed. Takes input with no trailing newline.

share|improve this answer

Japt, 22 bytes

"+Q ³sAJ fU"+Q ³sAJ fU

Standard quine framework with a few bytes added to fit this challenge. Truthy = match(es), falsy = null. Try it online!

         // Implicit: U = input string, A = 10, J = -1, Q = quotation mark
"..."+Q  // Take this string and concatenate a quotation mark.
³        // Repeat three times.
sAJ      // Slice off the first 10 and last 1 chars.
fU       // Match U to the result.
share|improve this answer

Mathematica, 63 bytes

StringMatchQ[ToString[#0, InputForm], RegularExpression[#1]] & 

Note the trailing space. Uses the standard Mma quine mechanism, and tests if it matches the regex.

share|improve this answer

Perl, 21 bytes

open 0;$_=<0>=~$_

17 bytes plus 4 bytes for -pl0. Run like this:

echo open | perl -pl0 quinean

The source file must contain only the code above (no shebang, no trailing newline). Outputs 1 if the regex matches and the empty string if it doesn't (the empty string is falsey in Perl).

Four bytes can be saved if the input is guaranteed not to end in a newline:

open 0;say<0>=~<>

Run like this:

echo -n open | perl -M5.010 quinean

say requires Perl 5.10+ and must be enabled with -M5.010. According to Meta, "the -M5.010, when needed, is free," giving a score of 17 bytes.

How it works

This is a simple variation on the standard "cheating" quine:

open 0;print<0>

This opens the file named in $0 and reads the contents with <0>.

$_=<0>=~$_ reads one line from the source file, does a regex match against the contents of $_ (which were read by the -p flag), and assigns the result to $_. -p prints $_ automatically at the end.

share|improve this answer

Jolf, 18 15 bytes

Supports the JS flavour of RegEx, I hope that's okay. Try it here!.



  $code.value#      the document's element "code" (the program container)
_h            i     and output if it has (matches) the input string (i.e. regex)
share|improve this answer
In which browser does this work? Both Chrome and Firefox complain that x.step is not a function. – Dennis Jan 12 at 14:27
@Dennis Huh. I must have broken the interpreter last night. What else is wrong? I currently am unable to debug, am at school. – Cᴏɴᴏʀ O'Bʀɪᴇɴ Jan 12 at 15:02
Good. Now add a shortcut to the document's element "code" so we can make it shorter. – zyabin101 Jan 12 at 15:26
@CᴏɴᴏʀO'Bʀɪᴇɴ It also gives a reference error for math. – Dennis Jan 12 at 15:26
@Dennis Ah, that's why. I forgot to update the HTML, I added math.js. I will revise when I arrive home, if that's not too late. (In about 4 ish hours) – Cᴏɴᴏʀ O'Bʀɪᴇɴ Jan 12 at 15:51

𝔼𝕊𝕄𝕚𝕟, 14 chars / 26 bytes (non-competitive)


Try it here (Firefox only).

Using a version with bug fixes written after the challenge.


⟮‼(ⒸⅩ222+ᶈ0)đï // implicit: ï=input
⟮               // copy block: copy following code for later use
 (ⒸⅩ222+ᶈ0)   // take convert 10222 to char, add stuff inside copy block
‼           đï // check if input matches resulting string
               // implicit output

NOTE: Copy blocks are NOT quine operators. They are meant to be more versatile alternatives to variable declarations.

share|improve this answer
I think you can save a byte by changing to 10. – lirtosiast Jan 12 at 5:59

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.