Help me redirecting

Question

Your task is to automatically complete URLs like the address bar in most browsers is doing. We will use the following (simplified) rules:

• If the input string starts with http://, ftp:// or https://, return the string unchanged.
• Otherwise, if the input string contains a dot ., e.g. in.put then the HTTP is assumed and http:// is prepended: http://in.put.
• Otherwise ftp:// is prepended, e.g. ftp://input when the input string was input.

Input

Any string which must not necessarily be a valid URL.

Output

The string modified according to the above rules.

Test Cases

dan-pc -> ftp://dan-pc
https://localhost/ -> https://localhost/
ftp://foo -> ftp://foo
http://foo -> http://foo
f.oo -> http://f.oo
derp.me -> http://derp.me
another.one/ ->http://another.one/
// -> ftp://// 
a://b -> ftp://a://b

This is code golf, shortest code wins. Good Luck!

Answer 1

R, 98 bytes

x=scan()
cat(`if`(grepl("^(https?|ftp)://",x),"",`if`(grepl("\\.",x),"http://","ftp://")),x,sep="")

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Answer 2

Perl 5 -p, 38 bytes

m%://%||s%.*\.%http://$&%||s%^%ftp://%

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Answer 3

Ruby, 63 56 55 bytes

->a{a[%r*(https?|ftp)://*]?a:"#{a[?.]?'ht':?f}tp://"+a}

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Answer 4

Swift, 147 133 bytes

Thanks to Herman L for saving 14 bytes.

Sadly, NSRegularExpression would've taken away lots of precious bytes.

import Foundation;let s=readLine()!,h=["http://","https://","ftp://"];print(h.contains{s.hasPrefix($0)} ?s:h[s.contains(".") ?0:2]+s)

Prettyfied:

import Foundation

let s = readLine()!, h = ["http://","https://","ftp://"]
print(h.contains{ s.hasPrefix($0) } ? s :h[s.contains(".") ? 0 : 2] + s)

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Answer 5

JavaScript (Firefox 52), 41 bytes

s=>new URL(s,/\./.test(s)?'http:':'ftp:')

If a string is required for output, add 3 bytes +'' at the end. (Notice this solution may add a trailing / at the end of domain name since they are the same URL)

f=
s=>new URL(s,/\./.test(s)?'http:':'ftp:')

t=s=>console.log(`${s} -> ${f(s)}`)

t('example.com')
t('example')
t('http://example')
t('https://example')
t('ftp://example')
t('http://example.com')
t('https://example.com')
t('ftp://example.com')

It seems this only works on Firefox 52 ESR but not Firefox 60 or Chrome 65. So sad.

Answer 6

PHP, 59 bytes

<?=strpos($s=$argn,':')?$s:(strpos($s,'.')?ht:f)."tp://$s";

To run all the tests:

cat <<EOF | php -nF <filename>
dan-pc
https://localhost/
ftp://foo
http://foo
f.oo
derp.me
another.one/
EOF

(Put a newline before the <?= for formatting, not required for one line of input)

Or just one at a time:

echo '<input>' | php -nF <filename>

Or Try it online!

Answer 7

Java 8, 74 72 bytes

s->s.matches("(https?|ftp)://.*")?s:(s.contains(".")?"ht":"f")+"tp://"+s

-2 bytes thanks to @HermanLauenstein.

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Explanation:

s->                   // Method with String as both parameter and return-type
  s.matches("(https?|ftp)://.*")?
                      //  If the input starts with one of
                      //  "http://", "https://", or "ftp://"
   s                  //   Return it as is
  :                   //  Else:
   (s.contains(".")?  //   If it contains a dot
     "ht"             //    Start with "ht"
    :                 //   Else:
     "f")             //    Start with "f"
   +"tp://"+s         //   And append "tp://" and the input-String

Answer 8

Retina, 64 bytes

^(?!(https?|ftp)://)(?=.*\.)
http://
^(?!(https?|ftp)://)
ftp:// 

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Answer 9

JavaScript, 64 bytes

x=>x.match`^(https?|ftp)://`?x:`${/\./.test(x)?'ht':'f'}tp://`+x

JavaScript, 51 50 bytes, Real life assumption

x=>x.match`//`?x:`${/\./.test(x)?'ht':'f'}tp://`+x

Thank tsh for 1 byte

Answer 10

GolfScript, 58 55 bytes

.'://':a/.,(\0=['https'.4<'ftp']:l?)*{}{.'.'?)!)l=a@}if

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This is my first GolfScript program, so I expect there is a lot room for golfing.

Explanation:

.'://':a/.,(\0=['https'.4<'ftp']:l?)*{}{.'.'?)!)l=a@}if Full program, implicit input
.                                                       Copy input
 '://':a                                                Push '://', and assign it to a
        /.                                              Split input at '://' and copy
          ,(                                            Push length of the result - 1 (<==> '://' in input)
            \0=                                         Pull up the array and get the first element
               ['https'.4<'ftp']:l                      Push [ 'https', 'http', 'ftp' ] and assign it to l
                                  ?)                    Test if first element is in that array
                                    *{}{            }if If at least one of those values is false
                                        .'.'?)          Push whether the input contains a dot
                                              !)        Logical not and increment:
                                                              '.' in input -> 1
                                                           no '.' in input -> 2
                                                l=      Get that element of l ([ 'https', 'http', 'ftp' ])
                                                  a@    Append a ('://') and input
                                                        Implicit output

Answer 11

Python 2, 87 85 bytes

lambda s:re.match('(https?|ftp)://',s)and s or['f','ht']['.'in s]+'tp://'+s
import re

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-2 bytes thx to Titus and wastl

Answer 12

Pyth, 58 bytes^SBCS

J"://"I:Q."(|e<UGÐÌ@ãy!'"ZQ.?I}\.Q++"http"JQ.?++"ftp"J

Test suite

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