Insist on an answer

Question

At runtime, keep prompting for a line of input until the user inputs something (other than an empty newline), i.e. does not just press Enter or OK. Output or result is neither required nor prohibited.

Pseudo-code 1

myform = new form("GUI")
myform.mytxt = new editfield("")
myform.ok = new button("OK")
repeat
  waitfor(myform.ok,"click")
until myform.mytxt.content <> ""

Pseudo-code 2

LET TEXT = ""
WHILE TEXT = "" DO
  TEXT = PROMPT("")
ENDWHILE

Example 1

Program runs and immediately pops up a form with a single text field and an OK button.
User clicks the OK button.
Nothing happens.
User pastes "hello world" into the text field and clicks the OK button.
Program terminates.

Example 2

Function is called and immediately displays a blank line and a blinking cursor.
User presses Enter.
Cursor moves down one line.
User presses Enter.
Cursor moves down one line.
User presses PPCGEnter
Function returns.

Answer 1

TI-BASIC, 2 bytes

:Prompt X

TI-BASIC does this automatically. Once input is given, it will quit.

Here is a GIF:

Watch the count on the enter key in the Key Press History. Created with TI-SmartView CE and ezgif.com.

Answer 2

Python 3, 18 bytes

while''==input():0

Try it online!

Answer 3

JavaScript, 37 22 17 bytes

while(!prompt());

while(!prompt());

Explanation

The while keyword starts the while loop. In the condition of the loop, !prompt() asks for input and checks whether it is given or not. If it isn't given, the body of the loop is executed, which in our case is empty, then the interpreter goes back to the loop condition. The same process happens over and over again until the user gives the input.

Answer 4

sed, 4

/./q

Waits for a line of input that has 1 or more characters, then quits.

Try it online. But it works better on a live shell:

sed '/./q'

Answer 5

Java, 55 bytes

void f()throws Exception{while(System.in.read()==10);}}

If I remember correctly (it's been a while since I've been active on PPCG), my program can just be a function.

This is system specific; it only works on systems where the end-of-line character is a single newline. If the end-of-line character is instead a carriage return, replace the 10 with 13. On Windows, this doesn't work, as end-of-line on windows is \r\n.

This makes use of the fact that I can read directly from System.in.

Answer 6

HTML5, 33 22 bytes

<form><input required>

<form><input required>

Explanation

The required attribute on the <input> causes the browser to inform the user "this field is required"-sort-of-message, if they do not enter a value. However, when they enter a value, the value is sent to the URL of the action attribute of the <form> (which in our case is the current file itself, since we haven't specified any value explicitly).

This was tested on the latest version of Google Chrome (version 55.0). May work in other browsers and versions.

Answer 7

Pyth, 3 bytes

W!w

Try it online!

Translated to Python:

while Pnot(input()):
 pass

Answer 8

Jelly, 3 bytes

ɠṆ¿

Not much to look at on TIO, I'm afraid.

Try it online!

How it works

This is a niladic program, meaning that it takes no input arguments. The implicit argument and return value are both 0 in this case.

¿ (while) is a quick that pops two links from the link stack: a condition (Ṇ) and a body.

Ṇ is a monadic atom: flat logical NOT. If the previous return value is falsy (here, 0 or an empty string), it returns 1 and the body is called.

ɠ is a niladic atom; it reads a raw line from STDIN and returns the result.

Once ɠ reads a non-empty line, Ṇ returns 0 and we break out of the loop.

Answer 9

brainfuck, 26 bytes

+[>,----------[[-]<[-]>]<]

Try it online!

Answer 10

Perl 5, 8+1 (-p or -n flag) bytes

/./&&die

Takes input from stdin and dies as soon as the regex matches anything except a newline.

Answer 11

C, 52 bytes, 33 bytes, 29 bytes

-19 bytes thanks to Justin

-4 bytes thanks to Christoph

main(){while(getchar()==10);}

10 is equal to '\n' - In case this isn't obvious.

Answer 12

Bash, 51 bytes (39 without "#!/bin/bash")

It's my first time participating in PPCG, so dont be to rude ;D

#!/bin/bash
read a
while [ -z "$a" ]
do
read a
done

Answer 13

R, 27 24 23 22 bytes

while(!sum(scan()^0))t

Takes input from stdin, and repeat as long as input is of length 0. Cut off some bytes due to Jarko Dubbeldam and MickyT. Replaced the {} with t to save another byte.

Answer 14

Java, 128 126 bytes

2 bytes thanks to Kevin Cruijssen.

import java.util.*;class a{public static void main(String[]a){for(Scanner s=new Scanner(System.in);s.nextLine().isEmpty(););}}

Try it online!

Answer 15

AWK, 8 11 bytes

NF{exit}

Wait for input. If the number of fields in input is more than 0, exit.

EDIT:

I've just realized that this doesn't work for input containing whitespace characters only. IFS needs to be set to empty string using -F "" command line option. Therefore +3 bytes.

Try it online!

Answer 16

C# (.NET Core), 66 bytes

class C{static void Main(){for(;System.Console.ReadLine()!="";);}}

Try it online!

-6 bytes thanks to raznagul.

Answer 17

QBasic 4.5, 15 bytes

INPUT a$:IF a$=""THEN RUN

Asks for input, then checks if any was given. If not, RUN restarts the program.

Answer 18

Ruby, 13 bytes

gets until/./

I wish gets took a Regexp argument.

Answer 19

PHP, 18 bytes

while(!readline())

Answer 20

SpecBAS - 34 bytes

1 DO : INPUT a$: LOOP UNTIL a$<>""

Just loops until non-empty string is entered.

Answer 21

Perl, 15 12 bytes (11 + -n flag)

-3 bytes thanks to manatwork

1/0if$/ne$_

Explanation:

The -n flag places a read loop around the program, turning it into:

LINE:
while (<>) {
    1/0 if $/ ne $_  # Spaces added for clarity.
}

Where "<>" reads a line from stdin to the variable $_. If the line contained more than the ending newline (ne is string inequality, $/ is the input record separator which defaults to newline), a division by zero is performed which causes the program to output an error message and terminate.

Answer 22

Mathematica, 26 20 bytes

For[,Input[]==Null,]

Answer 23

Haskell, 19 17 bytes

f=do""<-getLine;f

Defines a function f that if it reads the empty line calls itself again. When reading a non-empty line an exception is raised and the recursion is stopped.

Edit: @Laikoni replaced the parameter with a pattern match and saved 2 bytes. Thanks!

Answer 24

Aceto, 9 5 4 bytes

read a value, negate it (!; implicitly casting to a boolean), and mirror horizontally if the value is truthy (|).

!
r|

Answer 25

Java, 66 64 60 bytes

int a(){return!System.console().readLine().isEmpty()?0:a();}

My first Java answer, would love some tips!

Answer 26

Charcoal, 4 bytes

Ｗ¬Ｓω

Explanation

Ｗ      While
  ¬Ｓ   Logical not of string input
     ω  Print ""

Answer 27

05AB1E, 5 bytes

[IõÊ#

Explanation:

[     Start infinite loop
 I    One line of input
   Ê  Not equal to
  õ   Empty string
    # Break if true

Try it online!

Answer 28

PowerShell, 20 Bytes

for(;!(read-host)){}

runs a for loop,

read-host prompts for input

if read-host returns nothing it evals to false, so we invert that !(...) and use that as the loop end check.

much shorter than any do{$a=read-host}while($a-eq"") type solution involving variables.

Answer 29

Swift, 22 bytes

while readLine()==""{}

Answer 30

CJam, 5 bytes

{l!}g

Try it online! (TIO doesn't really show the proper behaviour)

Explanation

{      e# Do:
 l     e#  Read next line of input
  !    e#  Boolean negate (empty strings are falsy)
   }g  e# Pop the top of stack, if truthy, repeat.