What's the file extension?

Question

Your challenge is to find the file extension of a provided filename:

hi.txt -> txt or .txt
carrot.meme -> meme or .meme
lol (undefined behavior)
what..is..this..file -> file or .file
.bashrc -> bashrc or .bashrc
T00M@n3KaPZ.h0wC[]h -> h0wC[]h or .h0wC[]h
agent.000 -> 000 or .000

You must get the text from the last . or after the last . to the end of the string. The first capturing group match of the regular expression /\.([^.]+)$/ works, and so does splitting the input on .s and returning the last one.

The file name will always contain at least one ., but it may contain multiple .. (see examples)

The input will always match ^[.a-zA-Z0-9^!\[\]{}@$%+=]+$.

Please consider using the Sandbox in the future to get feedback on your challenges before posting them to the main site. — Mego, May 16 '17 at 20:45
codegolf.meta.stackexchange.com/a/12432/59376 - Got this idea from your challenge. — Magic Octopus Urn, May 16 '17 at 21:51
why the negative votes? Is this challenge "exceedingly trivial" or so ? — Abel Tom, May 17 '17 at 5:09
@AbelTom edit history would suggest downvotes were for the lack of specifications in the first draft of this question. — Patrick Roberts, May 17 '17 at 5:12

Erik the Outgolfer · Accepted Answer · 2017-05-17 12:40:29Z

2

Pyth, 5 bytes

ecz\.

try it here

answered May 17 '17 at 12:40

Erik the Outgolfer

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ASCII-only · Accepted Answer · 2017-05-17 13:20:16Z

2

Charcoal, 6 4 bytes

-2 bytes thanks to Erik the Outgolfer

⊟⪪Ｓ.

Try it online!

Explanation

⊟      Pop
  ⪪ .  Split on "."
   Ｓ  Next input as string
       Implicit print of value

edited May 17 '17 at 13:20

answered May 17 '17 at 4:48

ASCII-only

4,68714 silver badges38 bronze badges

\$\begingroup\$ Can't you use ⊟x instead of §x±¹? \$\endgroup\$ – Erik the Outgolfer May 17 '17 at 13:13

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theblitz · Accepted Answer · 2017-05-17 13:40:53Z

2

REXX 53

parse value reverse(arg(1)) with e "." 
say reverse(e)

answered May 17 '17 at 13:40

theblitz

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TheLethalCoder · Accepted Answer · 2017-05-17 15:20:40Z

2

C#, 35 bytes

s=>s.Substring(s.LastIndexOf("."));

Try it online!

edited May 17 '17 at 15:20

answered May 17 '17 at 14:10

TheLethalCoder

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Julian Wolf · Accepted Answer · 2017-05-17 16:32:05Z

2

Haskell, 32 30 29 bytes

-1 byte thanks to Laikoni

r=reverse
r.fst.span(/='.').r

self-explanatory

edited May 17 '17 at 16:32

answered May 17 '17 at 15:32

Julian Wolf

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1

\$\begingroup\$ takeWhile can be shortened to fst.span. \$\endgroup\$ – Laikoni May 17 '17 at 16:17

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Downgoat · Accepted Answer · 2017-06-09 01:12:34Z

2

Cheddar, 16 bytes

@.sub(/.*\./,"")

simple regex solution. Alternative solution using split:

@.split('.')[-1]

answered Jun 9 '17 at 1:12

Downgoat

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programmer5000 · Accepted Answer · 2017-10-29 18:03:49Z

2

JS (ES6), 26 25 bytes

x=>/\.([^.]+)$/.exec(x)[1]

-1 byte thanks to Shaggy

document.querySelector('pre').innerText = (x=>/\.([^.]+)$/.exec(x)[1])("example.txt")

<input oninput = "document.querySelector('pre').innerText = (x=>x.match(/\.([^.]+)$/)[1])(this.value)" value = "example.txt">
<pre></pre>

Alternate, 29 bytes:

x=>(y=x.split`.`)[y.length-1]

edited Oct 29 '17 at 18:03

answered May 16 '17 at 20:35

programmer5000

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\$\begingroup\$ Rulw seem allow x=>/\.[^.]+$/.exec(x) \$\endgroup\$ – l4m2 Mar 15 '18 at 19:45

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streetster · Accepted Answer · 2017-10-30 08:54:52Z

K (oK), 6 bytes

Solution:

*|"."\

Try it online!

Examples:

*|"."\"whats.up.txt"
"txt"
  *|"."\"T00M@n3KaPZ.h0wC[]h"
"h0wC[]h"

Explanation:

Split \ the input on ".", reverse | this list, and then take the first * one. K is interpreted right-to-left:

*|"."\ / the solution
  "."\ / "." split (\),
 |     / reverse
*      / first

Cinaski · Accepted Answer · 2017-10-30 09:07:53Z

2

Ohm v2, 5 bytes

I..ï⁾

Try it online!

answered Oct 30 '17 at 9:07

Cinaski

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Dom Hastings · Accepted Answer · 2017-10-30 13:08:20Z

2

Perl 5, 8 bytes

7 bytes code + 1 for -p.

s;.*\.;

Try it online!

answered Oct 30 '17 at 13:08

Dom Hastings

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Pavel · Accepted Answer · 2018-03-11 18:52:40Z

2

C# (Visual C# Interactive Compiler), 22 bytes

s=>s.Split('.').Last()

Implicit using System.Linq; FTW!

Try it online!

answered Mar 11 '18 at 18:52

Pavel

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TheLethalCoder · Accepted Answer · 2018-03-12 09:02:51Z

2

C#, 47 34 27 bytes

System.IO.Path.GetExtension

Saved 6 bytes thanks to @totallyhuman.

Try it online!

edited Mar 12 '18 at 9:02

answered May 17 '17 at 12:20

TheLethalCoder

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\$\begingroup\$ Since it's a built in I think you don't need the lambda. System.IO.Path.GetExtension. \$\endgroup\$ – milk May 18 '17 at 0:57
\$\begingroup\$ @milk Of course I do, that's just a method, it won't return .ext from file.ext because with just a method there's no way of passing the file.ext in. \$\endgroup\$ – TheLethalCoder May 18 '17 at 7:51
1

\$\begingroup\$ This is all you have to do. \$\endgroup\$ – totallyhuman Mar 11 '18 at 14:50
\$\begingroup\$ @totallyhuman Thanks, saved another byte by dropping the trailing semi colon to. \$\endgroup\$ – TheLethalCoder Mar 12 '18 at 9:03

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Tarryk Ttmm · Accepted Answer · 2018-03-13 00:14:26Z

2

JavaScript, 21 bytes

x=>x.split('.').pop()

Explanation:

This code takes x.txt and turns it into a array. The last element of the array is the file type. This code uses the pop function to remove the last element. In the process, the pop function returns the last element.

edited Mar 13 '18 at 0:14

answered Mar 11 '18 at 0:09

Tarryk Ttmm

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\$\begingroup\$ +Dennis, I have turned it into a arrow function. Does this comply with the rules? \$\endgroup\$ – Tarryk Ttmm Mar 13 '18 at 0:15
\$\begingroup\$ Yes, it is fine now. :) By the way, StackExchange uses @ to ping people, not +. \$\endgroup\$ – Dennis Mar 13 '18 at 0:18
2

\$\begingroup\$ Save 2 bytes with x=>x.split`.`.pop(). \$\endgroup\$ – Grant Miller Mar 14 '18 at 2:02

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sirtomato999 · Accepted Answer · 2018-03-13 23:05:42Z

2

Python 3, 46 bytes

-8 bytes thanks to Wheat Wizard and Scrooble

import sys
print(sys.argv[1].split('.')[-1])

EDIT: I fixed the code, and the filename is a command-line argument

edited Mar 13 '18 at 23:05

answered Mar 11 '18 at 17:32

sirtomato999

212 bronze badges

1

\$\begingroup\$ Welcome to the site! This doesn't appear to work, so you should either fix, or delete this answer. \$\endgroup\$ – caird coinheringaahing Mar 11 '18 at 17:55
\$\begingroup\$ This works for 54 \$\endgroup\$ – NoOneIsHere Mar 11 '18 at 17:57
\$\begingroup\$ To get the last item of a list you can use -1 as the index instead of len(a)-1. You could also probably change your input format to reduce the number of bytes. \$\endgroup\$ – Wheat Wizard Mar 11 '18 at 18:21
\$\begingroup\$ Adding to WW's suggestion: if you use -1 rather than len(a)-1, you no longer need the assignment and can save quite a few bytes. \$\endgroup\$ – Khuldraeseth na'Barya Mar 11 '18 at 21:12

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jrtapsell · Accepted Answer · 2018-03-14 00:51:10Z

Kotlin, 17 bytes

split(".").last()

Beautified

split(".").last()

Test

data class Test(val input: String, val output: String)

val test = listOf(
        Test("hi.txt", "txt"),
        Test("carrot.meme", "meme"),
        Test("what..is..this..file", "file"),
        Test(".bashrc", "bashrc"),
        Test("T00M@n3KaPZ.h0wC[]h", "h0wC[]h"),
        Test("agent.000", "000")
)

fun String.f() =
split(".").last()

fun main(args: Array<String>) {
    for ((i, o) in test) {
        if (o != i.f()) {
            throw AssertionError()
        }
    }
}

TIO

TryItOnline

rafa11111 · Accepted Answer · 2018-03-14 02:05:06Z

FORTRAN 90, 87 bytes

CHARACTER(99)F,L
READ*,F;DO I=1,LEN(F)
IF(F(I:I)=='.')L=F(I:LEN(F))
ENDDO
PRINT*,L
END

A shorter version in FORTRAN 90.

FORTRAN 77, 137 bytes

      PROGRAMC;IMPLICITCHARACTER*99(F)
      READ*,F;DOI=LEN(F),1,-1;IF(F(I:I).EQ.'.')THEN
      PRINT*,F(I:LEN(F));EXIT;ENDIF;ENDDO;END

There is no space in PROGRAM C, nor in IMPLICIT CHARACTER. It works (!) in gfortran, but I'm not sure it works in others compilers. The program takes input from stdin and outputs the extension with the period. The total length of the file name is limited by 99.

oktupol · Accepted Answer · 2018-03-14 12:36:25Z

2

V, 4 bytes

òdt.

Try it online!

Recursively delete everything up to, but not including the next .

answered Mar 14 '18 at 12:36

oktupol

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HatsuPointerKun · Accepted Answer · 2018-03-14 12:47:16Z

C++, 73 bytes

I'm a bit surprised that no one tried C++, since it's an easy one :

#include<string>
auto e=[](std::string s){return s.substr(s.rfind(46));};

And the code to test ( may have to iostream, initializer_list, and exception ) :

std::initializer_list<std::string> test{
    "hi.txt", // .txt
    "carrot.meme", // .meme
    "lol", // invalid string position
    "what..is..this..file", // .file
    ".bashrc", // .bashrc
    "T00M@n3KaPZ.h0wC[]h", // .h0wC[]h
    "agent.000" // .000
};

for (const auto& a : test) {
    try {
        std::cout << e(a) << '\n';
    }
    catch (std::out_of_range& r) {
        std::cout << "out of range exception : " << r.what() << '\n';
    }
}

And, as you may expect, like compilers, if there's undefined behavior, there's no undefined behavior. If there's no file extension, the function will throw a std::out_of_range exception, as said in cppreference

12Me21 · Accepted Answer · 2018-03-15 15:03:22Z

2

SmileBASIC, 45 bytes

INPUT S$@L
E$=POP(S$)+E$ON"."==E$[0]GOTO@L?E$

Outputs extension with the period.

edited Mar 15 '18 at 15:03

answered Mar 13 '18 at 17:47

12Me21

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Gabriel Mills · Accepted Answer · 2018-10-26 22:54:09Z

2

PowerShell, 34 26 bytes

-8 bytes thanks to @mazzy

(Read-Host).Split('.')[-1]

Takes input from STDIN. Actually managed to golf it down shorter than the built-in.

PowerShell, 20 bytes

($args-split'.')[-1]

Takes input from commandline arguments. Big thanks to @mazzy again!

PowerShell (with built-in), 36 bytes

[IO.Path]::GetExtension((Read-Host))

edited Oct 26 '18 at 22:54

answered Oct 26 '18 at 14:27

Gabriel Mills

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1

\$\begingroup\$ you can save some bytes. try this ($args-split'.')[-1] see About Automatic Variables \$\endgroup\$ – mazzy Oct 26 '18 at 16:38

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totallyhuman · Accepted Answer · 2017-05-16 20:48:53Z

1

Python 2, 25 bytes

lambda s:s.split('.')[-1]

Try it online!

answered May 16 '17 at 20:48

totallyhuman

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Magic Octopus Urn · Accepted Answer · 2017-05-16 21:04:00Z

1

Groovy, 37 bytes

{it.substring(it.lastIndexOf(".")+1)}

answered May 16 '17 at 21:04

Magic Octopus Urn

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\$\begingroup\$ How did someone already upvote this lol. Literally 1 second after I hit submit it hit +1. \$\endgroup\$ – Magic Octopus Urn May 16 '17 at 21:04

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marmeladze · Accepted Answer · 2017-05-16 21:20:24Z

1

Ruby, 21 bytes

->f{f.split('.')[-1]}

12 bytes

File.extname

answered May 16 '17 at 21:20

marmeladze

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sergiol · Accepted Answer · 2017-10-29 19:53:02Z

1

Tcl, 21 bytes

puts [file ext $argv]

Try it online!

answered Oct 29 '17 at 19:53

sergiol

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EricShermanCS · Accepted Answer · 2017-10-29 21:08:37Z

1

Julia, 22 bytes

g(n)=split(n,'.')[end]

answered Oct 29 '17 at 21:08

EricShermanCS

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daniero · Accepted Answer · 2017-10-29 22:23:30Z

1

Ruby, 16 bytes

->s{s[/[^.]+$/]}

Try it online!

answered Oct 29 '17 at 22:23

daniero

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Wernisch · Accepted Answer · 2018-03-09 14:34:00Z

1

Excel, 58 bytes

=TRIM(RIGHT(SUBSTITUTE(A1,".",REPT(" ",LEN(A1))),LEN(A1)))

answered Mar 9 '18 at 14:34

Wernisch

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Taylor Scott · Accepted Answer · 2018-03-09 14:39:48Z

1

Excel VBA, 29 bytes

An anonymous VBE immediate window function that takes input via cell [A1] and outputs to the console. Return string is of the form .Extension.

?Mid([A1],InStrRev([A1],"."))

answered Mar 9 '18 at 14:39

Taylor Scott

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Taylor Scott · Accepted Answer · 2018-03-09 14:54:53Z

1

Yabasic, 34 bytes

A basic answer

Takes input as a string from STDIN, and outputs of the form .Extension to STDOUT.

Input""s$
?Mid$(s$,RInStr(s$,"."))

Try it online!

answered Mar 9 '18 at 14:54

Taylor Scott

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Taylor Scott · Accepted Answer · 2018-03-09 15:06:03Z

1

Google Sheets, 25 bytes

An anonymous worksheet function that takes input from cell A1 and outputs the detected file extension of the form Extension to the calling cell.

=RegexExtract(A1,"[^\.]+$

answered Mar 9 '18 at 15:06

Taylor Scott

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What's the file extension?

86 Answers 86

Pyth, 5 bytes

Charcoal, 6 4 bytes

Explanation

REXX 53

C#, 35 bytes

Haskell, 32 30 29 bytes

Cheddar, 16 bytes

JS (ES6), 26 25 bytes

K (oK), 6 bytes

Ohm v2, 5 bytes

Perl 5, 8 bytes

C# (Visual C# Interactive Compiler), 22 bytes

C#, 47 34 27 bytes

JavaScript, 21 bytes

Python 3, 46 bytes

Kotlin, 17 bytes

Beautified

Test

TIO

FORTRAN 90, 87 bytes

FORTRAN 77, 137 bytes

V, 4 bytes

C++, 73 bytes

SmileBASIC, 45 bytes

PowerShell, 34 26 bytes

PowerShell, 20 bytes

PowerShell (with built-in), 36 bytes

Python 2, 25 bytes

Groovy, 37 bytes

Ruby, 21 bytes

12 bytes

Tcl, 21 bytes

Julia, 22 bytes

Ruby, 16 bytes

Excel, 58 bytes

Excel VBA, 29 bytes

Yabasic, 34 bytes

Google Sheets, 25 bytes

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