Create a simple line editor

Question

In: a string without line breaks*
Allow the user to edit and submit the line
Out: the modified string (optionally with a trailing linebreak)

The line editor must at minimum allow the user to:

1. move a visible cursor left and right

2. insert and/or overwrite characters at the cursor position

3. remove characters at the cursor position

4. submit the new string, i.e. cease editing cause the modified string to be returned/printed/displayed/saved… (with no other text)

Appreciated, but not required:

• explanation of your code.

• link to an online testing site that can demonstrate your program/function

• an animated image demonstrating usage (TIO, for instance, does not allow interactivity)

Note:

• key-bindings are suggestions only

• GUI or visual styling is not required

Examples

In the following, the cursor is illustrated with _.

In: Just some text
Allow the user to edit:
 Just some text_  User presses ← (left arrow key) nine times
 Just ̲some text  User presses Del four times
 Just ̲ text  User presses any
 Just any_text  User presses Enter
Out: Just any text

In: Remove me
Allow the user to edit:
 Remove me_  User presses Backspace nine times
 _  User presses Enter
Out:  (empty string)

---

* To prevent trivial editor solutions, this must either be supplied via a different input method than the editing commands, or must be separated from them by a newline or similar.

Answer 1

JavaScript (ES6), 15 14 bytes

I don't understand why this is getting so many upvotes!

s=>prompt(s,s)

Saved a byte thanks to Adám's suggestion that I display the original input in the prompt.

---

Try It

f=
s=>prompt(s,s)
console.log(f("Edit this ..."))

Answer 2

Bash 4.x, 25 characters

read -ei "$*" t
echo "$t"

Sample run:

bash-4.3$ bash interactive.sh hello world
hello golfing world
hello golfing world

(Line 2 above was the interactive editing, line 3 the output of resulted text.)

Answer 3

APL (Dyalog), 5 bytes

⍞←⍞⋄⍞

This is a tradfn, so to use it, do

∇a
⍞←⍞⋄⍞
∇

And then call it by using a, after which you supply the starting string, and then you can edit the string.

Answer 4

C + NCURSES, 573 bytes

#include <curses.h>
i;j;k;s;c;p;int main(a,b)char**b;{char*q;char t[999];if(a&&(q=b[1]))while(*q)t[s++]=*q++;i=s;initscr();noecho();keypad(stdscr,1);do{for(j=0;j<i;j++)addch(t[j]);addch('|');for(j=i;t[j];j++)addch(t[j]);c=getch();switch(c){case KEY_LEFT:if(i)i--;break;case KEY_RIGHT:if(i<s)i++;break;case 8:case 127:case KEY_BACKSPACE:if(i){for(k=i-1;k<s;k++)t[k]=t[k+1];i--;s--;}break;case KEY_DC:if(i<s){for(k=i;k<s;k++)t[k]=t[k+1];s--;}break;default:if(c>31&c<127){for(k=s;k>i;k--)t[k]=t[k-1];t[i]=c;i++;s++;}}clear();}while(c!=10);printw(t);getch();endwin();return 0;}

Test

• Compile & Run with input Just some text.

• Press Left-Arrow button nine times.

• Press Delete button four times.

• Press a then n then y.

• Press Enter to terminate.

Detailed

#include <curses.h>

int main(int argc, char ** argv)
{
    char*q = 0;
    char t[999] = {0};
    int j = 0, k = 0;
    int i = 0; // cursor before first char
    int s = 0; // current size
    int c = 0; // current input
    int p = 0;

    // copy first command-line argument
    if(argc>0 && (q=argv[1]))while(*q)t[s++]=*q++; i=s;

    initscr(); // initiate NCURSES
    noecho(); // input does not echo on entry
    keypad(stdscr,TRUE); // handle all input

    do
    {
        // print current content with cursor
        for(j=0;j<i;j++) addch(t[j]);
        addch('|'); for(j=i;t[j];j++) addch(t[j]);

//      printw("\n\n> key %d pressed",c); // debug

        c = getch(); // read next char

        switch(c)
        {
            case KEY_LEFT: // left arrow; cursor left
            if(i > 0) i--;
            break;

            case KEY_RIGHT: // right arrow; cursor right
            if(i < s) i++;
            break;

            case 8: // backspace; remove previous char
            case 127:
            case KEY_BACKSPACE:
            if(i > 0)
            {
                for(k=i-1; k<s; k++) t[k]=t[k+1];
                i--;s--;
            }
            break;

            case KEY_DC: // delete; remove next char
            if(i < s)
            {
                for(k=i; k<s; k++) t[k]=t[k+1];
                s--;
            }
            break;

            default: // none of the above

            if(c > 31 && c < 127) // printable char
            {
                for(k=s; k>i; k--) t[k]=t[k-1];
                t[i] = c;i++;s++;
            }
        }

        clear(); // clear screen
        if(c == 10) break;
    }
    while(c);

    addch('\n');
    printw(t); // print final result
    getch(); // wait for any input
    endwin();
    return 0;
}

Answer 5

Bash + Vi/Vim, 14 bytes

echo $1>a;vi a

vi is aliased to vim on macOS, I don't know about other OSes.

Answer 6

HTML + JavaScript (ES6), 77 66 64 bytes

HTML

<input id=t

JavaScript

onkeyup=e=>e.which-13||alert(t.value);f=a=>t.value=a;

Saved 10 bytes thanks to Jörg Hülsermann and 2 bytes thanks to Luke.

onkeyup=e=>e.which-13||alert(t.value);f=a=>t.value=a;

f("Remove Me");

<input id=t>

Answer 7

Python 2, 275 200 bytes

Not a winner, but here it is:

from msvcrt import*
s=list(input())[::-1]
c=i=0
def p(a):print''.join(a)[::-1]
while'\r'!=c:p(s[:i]+['<']+s[i:]);c=getch();x=c!='\b';exec["s[i:i+1-x]=c*x","i=(i-1+2*(c<'\\t'))%-~len(s)"][x*' '>c]
p(s)

Explanation:

It works by reversing the input (with [::-1]), and excluding and inserting characters in that reversed input so that the cursor does not have to move. Reverses it again when printing.

Usage:

[Tab] key to move Right
[Ctrl+C] to move Left
[Backspace] to erase
[Return] to finish editing
Any other key, will be inserted into text

Example:

Using OP's example

In: Just some text
 Just some text>
 Just some> text User presses Ctrl+C five times
 Just > text  User presses Backspace four times
 Just any> text  User presses any
 Just any> text  User presses Enter
Out: Just any text

Inline editor version:

If you want the text to be editted inline, append ,'\r', at the end of the print statement:

def p(a):print''.join(a)[::-1],'\r',

Answer 8

VBScript, 23 40 bytes

MsgBox InputBox("",,Wscript.Arguments(0))

Answer 9

C#, 53 bytes

s=>{SendKeys.SendWait(s);return Console.ReadLine();};

Where s is a string to modify and the output is the new value.

SendKeys.SendWait: Sends the given keys to the active application, and then waits for the messages to be processed.

or 74 bytes if we are not in a Windows Forms context:

s=>{System.Windows.Forms.SendKeys.SendWait(s);return Console.ReadLine();};

Answer 10

Ruby, 9 19 22 84 bytes

->s{r=Readline;r.pre_input_hook=->{r.insert_text s;r.redisplay};r.readline}

This creates a Readline pre input hook that inserts the text s and then redisplays. After this, irb gets messed up so make sure to run this from a file. Run as a lambda, it takes the input string as an argument and returns the output string.

puts Readline.readline

This uses the Readline library to perform line editing. My previous answer only allowed backspaces.

puts gets

This is really, really self explanatory.

Edit: I have been asked for an explanation. This is equivalent to puts(gets). gets inputs a string with a line editor. puts outputs it.

Answer 11

PHP + HTML, 26 Bytes

<input value=<?=$_GET[0]?>

The Browser adds automatically the closing tag

$_GET Using a url like http://example.com?0=input as Input Creates in a HTML <input value=input

And this is the output for the string input

<input value=input

Answer 12

Tcl, 17

puts [gets stdin]

Online interpreters just suck to demonstrate it, then I showcase some images from a Windows command shell:

Test case 1

Test case 2

Answer 13

AHK, 32 bytes

InputBox,s,,,,,,,,,,%1%
Send,%s%

InputBox stores whatever is typed as the variable s and gives a starting prompt of the variable 1 which is the first passed parameter.
Send sends keystrokes to the current window. In this case, it'll be the contents of s.
MsgBox was an option but, for golfing, Send is 2 bytes shorter.

Answer 14

Excel VBA Immediate Window Command - 22 bytes

[a1]=inputbox(0,,[a1])

Answer 15

SmileBASIC, 138 bytes

DEF E S@L
WAIT
B=BUTTON(1)C=C-(B==4&&C)+(B>7&&C<LEN(S))I$=INKEY$()IF"\u0008"<I$THEN B=I$<"\u000E"S=SUBST$(S,C,B,I$*!B)?S?" "*C;1IF"\u0008"!=I$GOTO@L
END

Creates a function E with 1 argument and 0 outputs. (Output is displayed in the console)

The escaped characters should be the actual symbols, but they wouldn't show up here.

Controls:

Normal keys: Insert a character before the cursor.
Enter: Delete the character at the cursor.
Backspace: Submit.
D-pad left: Move cursor left.
All buttons except up, down, and left on the d-pad: Move cursor right.

Inserting/deleting characters is backwards so it's very annoying to use (but should still fulfill the requirements).

Just some text
1             
'(press right 5 times)
Just some text
     1
'(press enter 4 times)
Just  text
     1
'(press a)
Just a text
     1
'(press right)
Just a text
      1
'(...)
Just any text
       1
'(press backspace)

Answer 16

ZX Spectrum BASIC, 7 bytes

Trivial, included for completeness (INPUT and PRINT are one byte tokens each).

INPUT a$: PRINT a$

Answer 17

Windows command interpreter, 16 bytes

set/pa=
echo %a%

This is very trivial; the command interpreter is trivially a "line editor".

Answer 18

Commodore BASIC (C64Mini, C64/128, VIC-20 etc...) 179 tokenized BASIC bytes

This should be typed in business mode (upper/lower case characters)

 0a$="Just some text":?"{SHIFT+CLR/HOME}"a$"_":fOi=0to1step0:getk$:on-(k$<>"")goS2:goS1:nE
 1?"{CTRL+N}{CLR/HOME}"a$"_  ";:return
 2ifasc(k$)<>20thena$=a$+k$:on-(asc(k$)=13)goS4:return
 3if-(len(a$))thena$=leF(a$,len(a$)-1):goS4:return
 4?"{ARROW LEFT}{ARROW LEFT}{ARROW LEFT}  ":return

Allows basic text editing + delete + new line. Maximum size of a$ like all strings in Commodore BASIC is 255 characters, so any more than that will crash the program. I will find a way to do > 255 characters if that is necessary.