Insist on a new filename

Question

At runtime, keep prompting for a line of input until the user input is not the name of an existing file or directory or other file system item, relative to the current working directory. Then return/print that last inputted filename. You may assume that all user inputs will be valid filenames.

Pseudo-code 1

myform = new form("GUI")
myform.mytxt = new editfield("")
myform.ok = new button("OK")
repeat
  waitfor(myform.ok,"click")
until not filesystem.exists(myform.mytxt.content)
return(myform.mytxt.content)

Pseudo-code 2

LET TEXT = "."
WHILE HASFILE(TEXT) DO
  TEXT = PROMPT("")
ENDWHILE
RETURN TEXT

Examples of user input which will cause re-prompting when on TIO:

.
..
.env.tio
/
/bin/[
/lost+found

Examples of user input which will return when on TIO:

...
env.tio
../../bin/]
/lost/found

Answer 1

Batch, 37 bytes

@set/ps=
@if exist %s% %0
@echo %s%

(For some reason current Windows 10 CMD.EXE corrupts the title when it executes the %0.)

Answer 2

Mathematica, 33 28 bytes

f:=Input[]/._?FileExistsQ:>f

This assumes Mathematica's notebook environment where we can query input from the user with Input[]. The user input should be an actual string literal, so e.g. "ab/cd.ef" instead of just ab/cd.ef. The upside is that the input can be an arbitrary Mathematica expression that computes the input string.

This defines a symbol f which, when evaluated performs the required computation and ultimately evaluates to the first non-existent user input. It's essentially a nullary function, where we don't have to include ...[] to call it.

We can also save a bunch of bytes over a traditional If expression by making use of the pattern substitution operator /..

Answer 3

Perl 5 -ln, 12 10 bytes

-2 bytes thanks to @DomHastings

#!/usr/bin/perl -ln
-e||1/!say

Try it online!

Answer 4

Bash, 29

read f
[ -e $f ]&&$0||echo $f

Answer 5

PowerShell 2 (through 6), 35 bytes

while(Test-Path($x=Read-Host)){};$x

Read-Host waits for input (if given a string as a parameter, uses the string as a prompt). If the provided input is a filename (or folder name) for one that exists, Test-Path returns $true, and the do-nothing block {} executes, and it re-prompts for input. If Test-Path returns $false because the input is not an extant file or folder, the do-nothing block does not execute, and the input name is printed.

Answer 6

C (gcc), 62 bytes

main(){char b[99];while(scanf("%s",b)&&!access(b,0));puts(b);}

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main(){
    char b[99]; // Declare buffer b
    while (scanf("%s",b)&&!access(b,0));    // Take one line of input, and test if file is accessible (exists)
    puts (b);   // If doesn't exist, loop ends and print file
}

Answer 7

Funky, 40 bytes

tryfor)io.open(s=io.read())catchprint(s)

In true funky style, this uses keywords jammed against eachother, unmatching brackets and implicit keywords. Cleaned up, this looks like:

try{
    while(true){
        s = io.read()
        io.open(s)
    }
}catch(e){
    print(s)
}

Breakdown

try                                     // Try statement, this one is expected to fail.
   for)                                 // for) is a for loop with no arguments, which is functionally equivilent to a while(true) loop, much like for(;;)
       io.open(                         // Try to open a file relative to the CWD. If this fails to find a file, it will throw an error and escape the try/catch
               s=io.read()              // Read a line from STDIN and store it as s, this will still pass it to the arguments of the call.
                          )
                           catch        // When io.open fails
                                print(s)// Print out the last entered line.

Answer 8

Haskell, 76 bytes

import System.Directory
f=do x<-getLine;b<-doesPathExist x;last$pure x:[f|b]

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Returns IO x where x is the inputted name of the file that does not exist.

Ungolfed

import System.Directory

insist = do { file <- getLine;
              exists <- doesPathExist file;
              if exists then insist else pure file }

Answer 9

R, 66 51 bytes

while((s=readline())%in%list.files(a=T)){};print(s)

-15 bytes thanks to plannapus

Runs a potentially infinite loop, where on each iteration

1. A single line of user input is stored in the variable s
2. We check if the input is in the list of filenames for the working directory (the a=T option for list.files() must be used to pick up things like ..)
3. If s is in that list, we go to the next iteration; if not, we break the loop and print s.

Answer 10

Python 3, 55 bytes

import glob
s="."
while glob.glob(s):s=input()
print(s)

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-4 bytes thanks to ManfP
-6 bytes thanks to Rick Rongen

Answer 11

C#, 101 bytes

()=>{var s="";try{for(;;System.IO.File.GetAttributes(s=System.Console.ReadLine()));}catch{}return s;}

For each of the 4 valid return values:

• Try it online! (returns '...')

• Try it online! (returns 'env.tio')

• Try it online! (returns '../..bin/])

• Try it online! (returns '/lost/found)

Ungolfed

() =>
{
    var s = "";
    try
    {
        for(;; System.IO.File.GetAttributes(s = System.Console.ReadLine()));
    }
    catch {}
    return s;
}

Explanation

relies on the fact that File.GetAttributes() throws an exception if file system object specified in its argument doesn't exist.

Answer 12

Powershell 3.0, 75 bytes

$x=1;while($x){$i=Read-Host;$x=Test-Path("$PSScriptRoot\$i")};Write-Host $i

First attempt; I'm sure there are a few optimizations I could make.

A slightly more readable form:

$x=1;                                                                       # Make sure we enter our while loop.
     while($x){                                                             # While we keep getting file names,                   
               $i=Read-Host;                                                # Get input from the user
                            $x=Test-Path("$PSScriptRoot\$i")};              # Combine our path with the user input, and see if it already exists.
                                                              Write-Host $i # Return the final (valid) file name.

Answer 13

Java 9, 87 bytes

v->{String s;for(;new java.io.File(s=System.console().readLine()).exists(););return s;}

Ungolfed

TIO's JVM apparently has no system Console, so it's not testable there (see System.console()).

import java.util.function.*;
class Main {
  public static void main(String[] args) {
    Function<Void,String> f =


v->{
  String s;
  for(;new java.io.File(s=System.console().readLine()).exists(););
  return s;
}


;
    System.out.println(f.apply(null));
  }
}

Answer 14

JavaScript (Node.js), 158 118 bytes

require('readline').createInterface({input:process.stdin}).on('line',s=>require('fs').existsSync(s)||--console.log(s))

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Credit to @ConorO'Brien for coming up with shorter version. Inlined objects instead of using consts and utilizing error exit condition instead of explicitly exiting.

Answer 15

Clean, 100 94 bytes

import System.IO,System.File
Start w#(s,w)=evalIO getLine w
#(b,w)=fileExists s w
|b=Start w=s

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single-expression version:

import System.IO,System.File
Start w=(\(s,v)=(\(b,w)|b=Start w=s)(fileExists s v))(evalIO getLine w)

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Answer 16

Perl 6, 39 bytes

my$f=".";while $f.IO.e {$f=get};say $f;

This works in the REPL, but it doesn't seem to work properly in TIO.

Answer 17

PHP, 43 bytes

<?for(;file_exists($f=readline()););echo$f;

Run as CLI. Quite easy to understand.

Answer 18

Ruby, 40 39 37 bytes

{}while File.exist? gets.chomp
$><<$_

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Answer 19

APL (Dyalog), 17 bytes

{⍞}⍣{~⎕NEXISTS⍺}⍬

Try it online!

Answer 20

Kotlin, 67 bytes

val f={var s="."
while(java.io.File(s).exists()){s=readLine()!!}
s}

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Answer 21

Attache, 35 bytes

{While[FileExists[x:=Prompt[]],0]x}

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Alternative solutions

35 bytes: {If[FileExists[x:=Prompt[]],$[],x]}, recursive function.

37 bytes: {NestWhile[p:=Prompt,p[],FileExists]}, iterative function.

Answer 22

Min, 38 bytes

"." :a (a exists?) ("" ask @a) while a

Leaves last entered filename on the stack.

Explanation

"."         ; Put . on the stack. Every directory should contain this...
:a          ; Assign to a
(a exists?) ; A quot that checks if a exists in current directory
("" ask @a) ; Read line from stdin, assign to a
while       ; Do the second quote while the first leaves true on the stack
a           ; Leave a on the stack

Answer 23

SmileBASIC, 27 bytes

INPUT S$EXEC!CHKFILE(S$)?S$