Holy wars have been fought over spaces vs. tabs. (And of course spaces, being objectively superior, won.) —Alex A.

Some people still refuse to accept that which is clearly supreme. You've just received a file using the incorrect, bad, and inferior form of whitespace, and now the contents of the file are tainted and ruined.

You decide you might as well show the person who sent the file to you just how wrong they are—violently.


As the title suggests, your challenge is to take a file that contains one or more tabs:

this is an evil tab    onoes

and ruthlessly shatter them into pieces:

this is an evil tab


Note that the Stack Exchange software turns literal tabs into four spaces (because it's right), so tabs within this post will be displayed as four spaces. The input to your program, however, will contain actual tabs.


The solution should take a single string as input, which may contain printable ASCII, newlines, and tabs. There will always be at least a single tab in the input.

The output should be the same string, with the following rules applied:

  • Start the cursor at coordinates (0,0) and with a direction of right. The coordinates are (column,row), zero-indexed, and the direction is which way you should move the cursor after printing a character.

  • For each character in the string:

    • If it's a newline, move to coordinates (0,n), where n is the number of newlines in the string so far (including this one), and reset the direction to right.

    • If it's a tab, output two spaces, rotate the cursor direction 90 degrees clockwise, and output two more spaces, effectively "breaking" the tab in half. Here's a visual example, where a tab is represented as ---> and spaces as ·:



    • Otherwise, simply output the character at the cursor and move the cursor one step in the current direction.

Since you are reading the string from start to end, it is possible that you will have to write "on top" of existing characters—this is okay. For example, the input


spaces are superior

should result in an output of


spaces are superior

You may choose whether "broken tabs" should overwrite other characters—the original intention was that they do not, but the spec was ambiguous, so this is your decision.

Furthermore, after applying these rules, you may also

  • add or remove as many trailing spaces as you would like.

  • add a maximum of a single trailing newline.

The input will never contain trailing spaces; it will also never contain leading or trailing newlines. You may also always assume that you will never need to write to a column or a row less than 0 (i.e. off the screen).

Test case

Tabs in this test case are represented as ---> because otherwise SE gobbles them up.


Test case. Here's a tab--->there's a tab--->everywhere a tab--->tab--->this is some more text
blah blah blah blah blah blah--->blaah--->blaah--->blah--->blaaaaah--->blah--->blah--->blah--->blah--->blah


Test case. Here's a tab
blah                     t
blah blah blah blah blah blah
                         r     b
                         e     l  b
                      h  'h    a  l
                      a  sa    a  a
                      l   l    h  h
       this is some mobe tbxt

     b                   a
     a                   b

        bat a erehwyreve

Fancy animation:


  • This is , so the shortest code in bytes will win!
  • \$\begingroup\$ When you say the cursor has to start at (0,0) do you mean we need to clear the console first, or do you just mean the default position of the cursor by that? \$\endgroup\$ Sep 21, 2015 at 6:26
  • 19
    \$\begingroup\$ I'm voting to close this question as off-topic because it is full of hatred and blasphemy. \$\endgroup\$ Sep 21, 2015 at 6:53
  • 1
    \$\begingroup\$ Your animation looks so much like the ><> interpreter that I now want to see a self-modifying ><> entry. \$\endgroup\$
    – Sanchises
    Sep 21, 2015 at 8:48
  • 1
    \$\begingroup\$ I liked the hidden message in the opening paragraph but I have to disagree. \$\endgroup\$
    – wf4
    Sep 21, 2015 at 14:41
  • \$\begingroup\$ @MartinBüttner That just means the default position. \$\endgroup\$
    – Doorknob
    Sep 21, 2015 at 16:35

5 Answers 5


MATLAB, 144 bytes

The weapon of choice for dealing with strings is of course a language designed for manipulating numbers [citation needed]. Kidding aside, the great thing about Matlab is that it doesn't care if you assign to an array 'out of bounds': it will simply make a larger matrix. Furthermore, the default matrix element, 0, is rendered as a space instead of a null character the ASCII spec prescribes.

Tabs are simply a jump in coordinates, so no spaces are outputted for a tab.

function o=q(t)
u=2;v=0;x=1;y=1;n=1;for s=t
if s==9 x=x+u-v;y=y+v+u;a=v;v=u;u=-a;elseif s<11

I started out with 209 bytes, but some more careful golfing got rid of most of that; there's a lot of repetition in this code, so I did some trial-and-error which alternatives worked best. I don't think there's much space for more optimization with this code, but I'm always happy to be proven wrong. Edit: Tom Carpenter managed to prove me wrong; he managed to save 9 bytes which I optimized to save a whopping 29 bytes. Last byte saved by assuming there are no control characters (ASCII < 9) in the input - MATLAB strings aren't null-terminated.

  • \$\begingroup\$ Doesn't appear to work. I tried this q('hello<tab>my name<tab>is tom<tab>c'), but it something along the lines of Attempted to access o(11,-2); on line 7. Though this may be more to do with an issue in the question - if the cursor is heading backwards and goes beyond the first column what happens to the rest of the line. \$\endgroup\$ Sep 21, 2015 at 21:20
  • \$\begingroup\$ Yep, my bad I missed that bit. I'll go away now ;) \$\endgroup\$ Sep 21, 2015 at 21:27
  • 1
    \$\begingroup\$ You can save another 9 characters by removing the d variable and instead having 4 variables which for a loop to make the [1 0 -1 0] pattern as such: function o=q(t) u=1;v=0;w=-1;z=0;x=0;y=1;n=1;for s=t if s==9 x=x+2*u-2*v;y=y+2*v+2*u;a=z;z=w;w=v;v=u;u=a;elseif s==10 n=n+1;x=0;y=n;else x=x+u;y=y+v;o(y,x)=s;end end (obviously being in the comments it removed all the lines, so you'll have to reformat it like yours to see what I did) \$\endgroup\$ Sep 21, 2015 at 22:08
  • \$\begingroup\$ @TomCarpenter That's... really ugly. I love it. \$\endgroup\$
    – Sanchises
    Sep 22, 2015 at 7:42

Python 3, 272 270 266 262 255 253 244 bytes

 while 1:I+=[input()]
O=[M*[' ']for _ in[0]*M]
for l in I:
 for c in l:
for l in O[:m+1]:print(*l,sep='')

The \t should be an actual tab character.

The code works somewhat like Zach Gates' answer, first generating a M by M grid where M is the sum of the lengths of the lines. (That's a huge amount of excess, but makes the code shorter.) It then loops through the characters, placing them in the correct spots, keeping track of the bottommost visited row. Finally, it prints all the lines up to that row.

The output contains (usually a huge amount of) trailing spaces and 1 trailing newline.


Javascript (ES6), 264 245 bytes

Tried the "create a giant grid of spaces, fill and trim" approach, which ended up 19 bytes shorter than the other.

a=t=>(o=`${' '.repeat(l=t.length)}
`.map(q=>q.split``),d=x=y=z=0,s=c=>o[d>2?y--:d==1?y++:y][d?d==2?x--:x:x++]=c,[...t].map(c=>c=='\t'?(s` `,s` `,++d,d%=4,s` `,s` `):c==`

By modifying the second-to-last line like so, you can remove the large amount of trailing spaces on every line:


Try it here:

a=t=>(o=`${' '.repeat(l=t.length)}
`.map(q=>q.split``),d=x=y=z=0,s=c=>o[d>2?y--:d==1?y++:y][d?d==2?x--:x:x++]=c,[...t].map(c=>c=='\t'?(s` `,s` `,++d,d%=4,s` `,s` `):c==`

function submit(){ O.innerHTML = a(P.value.replace(/\\t|-+>/g,'\t')); }
<p>Input: (Use <code>\t</code> or <code>---></code> for a tab.)</p>
<textarea id=P rows="10" cols="40">this is an evil tab\tonoes</textarea>
<br><button onclick="submit()">Try it!</button>
<p>Output: (Looks best in full-page mode.)</p>
<pre id=O>

Explanation coming soon; suggestions welcome!


JavaScript (ES6), 180 183

Using template strings, there are some newlines that are significant and counted.

That's a function returning the requested output (padded with tons of trailing spaces)

There is little to explain: the rows are builded as neeeded. There is not a direction variable, just the 2 offset for x and y, as in clockwise rotation they are easily managed: dx <= -dy, dy <= dx

Test running the snippet below in Firefox

`?(x+=2*(d-e),y+=2*(e+d),[d,e]=[-e,d]):c<' '?(y=++r,e=x=0,d=1):(t=[...(o[y]||'')+' '.repeat(x)],t[x]=c,o[y]=t.join``,x+=d,y+=e),o=[r=x=y=e=0],d=1)&&o.join`

// TEST  

// Avoid evil tabs even in this source 
O.innerHTML = f(`Test case. Here's a tab--->there's a tab--->everywhere a tab--->tab--->this is some more text
blah blah blah blah blah blah--->blaah--->blaah--->blah--->blaaaaah--->blah--->blah--->blah--->blah--->blah`
<pre id=O></pre>

  • \$\begingroup\$ I wish all languages had [x,y]=[expr1,expr2]... \$\endgroup\$
    – Sanchises
    Sep 23, 2015 at 18:38

Python 2, 370 369 368 bytes

Thanks to @sanchises and @edc65 for saving me a byte each.

u=raw_input().replace('\t','  \t  ')
d,r=0,[[' 'for _ in G]for _ in G]
for t in G:
 for c in u[t]:
  if c=='\t':d=(d+1)%4
  if c!='\t':
   if c.strip():r[y][x]=c
   if d<1:x+=1
   if d==1:y+=1
   if d==2:x-=1
   if d>2:y-=1
r=r[:max(i for i,n in enumerate(r)if J(n).strip())+1]
for i in r:print J(i).rstrip()

It generates the largest grid possible and then loops around, character by character, switching direction at each tab.

  • \$\begingroup\$ Hint: if !d and if d>2 \$\endgroup\$
    – Sanchises
    Sep 21, 2015 at 21:39
  • \$\begingroup\$ !d is not valid syntax. @sanchises Thanks for the d>2 tip, though. \$\endgroup\$
    – Zach Gates
    Sep 21, 2015 at 21:42
  • \$\begingroup\$ Sorry, I don't actually know python :) Just sort of assumed it would work like that. \$\endgroup\$
    – Sanchises
    Sep 21, 2015 at 21:46
  • \$\begingroup\$ I too don't understand python, but if d in 0...3, d==0 -> d<1 \$\endgroup\$
    – edc65
    Sep 21, 2015 at 22:06
  • \$\begingroup\$ Yep, you're right. Thanks for the byte. @edc65 \$\endgroup\$
    – Zach Gates
    Sep 21, 2015 at 22:10

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