# Regular Expression help

**URL:** <https://www.ruby-forum.com/t/regular-expression-help/147668>\
**Category:** Rails\
**Created:** [September 4, 2008, 3:29am UTC](https://www.ruby-forum.com/t/regular-expression-help/147668 "2008-09-04T03:29:02Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![brendon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/5f9b8f/32.png) [@brendon](https://www.ruby-forum.com/u/brendon)\
**Post date:** [September 4, 2008, 3:29am UTC](https://www.ruby-forum.com/t/regular-expression-help/147668/1 "2008-09-04T03:29:02Z")

</div>

Hi everyone, I hope it’s appropriate to post this question here. I  
couldn’t find anywhere else to post it (posting to the Ruby group  
didn’t work). I’m trying to write a regular expression to turn this  
string:

‘johnny went to the [shops] and played [games,soccer,foot ball] with  
others.’

into this:

[‘johnny went to the’, [‘shops’], ‘and played’, [‘games’, ‘soccer’,  
‘foot ball’], ‘with others.’]

Key features are that white space needs to be stripped from around the  
snippets, and I need to be able to determine which parts are just  
normal text and which parts are to be used as gaps where people fill  
in the missing info. If you haven’t already figured it out, this is  
for a children’s quiz engine. When a phrase appears in square brackets  
it’s a blank, the system will display a text box for the user to type  
into. If there are multiple items in the square brackets seperated by  
comma’s (and optional spaces around the comma’s by lazy users) then  
the system will display the choices in a random order in a drop down  
box (the first choice in the list is the correct one).

I’ve had a long go at it myself but I just don’t fully grasp the  
regexp language:

irb(main):027:0\> ‘johnny went to the [shops] and played  
[games,soccer,foot ball]  
with others.’.split(/[(?:([(?:\s)\w(?:\s)]+)(?:,([(?:\s)\w(?:\s)]  
+))\*)]/)  
=\> ["johnny went to the ", “shops”, " and played “, “games”, “foot  
ball”, " with  
others.”]

I’ve tried doing groupings but it seems to make things worse 🙂

Any help would be truly appreciated 🙂

Cheers,

Brendon

---

<div class="post-metadata">

**Author:** ![brendon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/5f9b8f/32.png) [@brendon](https://www.ruby-forum.com/u/brendon)\
**Post date:** [September 5, 2008, 5:24pm UTC](https://www.ruby-forum.com/t/regular-expression-help/147668/2 "2008-09-05T17:24:10Z")

</div>

This is kinda ghetto (particularly needing to check chunk.length) but it  
works on your sample string.

def parse\_item(lin)  
ret = Array.new  
re = Regexp.new(/([^[]]+?([|]))+?/)  
lin.split(re).each do |chunk|  
if chunk.length \> 1 then  
case chunk  
when /]$/  
# bracketed option list  
ret \<\< chunk[0…-2].split(’,’)  
else  
# plain chunk of text  
ret \<\< chunk.gsub(/[$/, ‘’).strip  
end  
end  
end  
ret.inspect  
end

HTH,

-Roy

---

<div class="post-metadata">

**Author:** ![brendon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/5f9b8f/32.png) [@brendon](https://www.ruby-forum.com/u/brendon)\
**Post date:** [September 8, 2008, 2:53am UTC](https://www.ruby-forum.com/t/regular-expression-help/147668/3 "2008-09-08T02:53:28Z")

</div>

Woah dude! Thanks for that 🙂 I’ll work my way through understanding  
it now 🙂

Cheers!

Brendon

---

<div class="post-metadata">

**Author:** ![brendon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/5f9b8f/32.png) [@brendon](https://www.ruby-forum.com/u/brendon)\
**Post date:** [September 10, 2008, 11:12am UTC](https://www.ruby-forum.com/t/regular-expression-help/147668/4 "2008-09-10T11:12:08Z")

</div>

Here’s what we came up with using StringScanner:

def processed\_answer

```
scanner = StringScanner.new(correct_answers)

# last position the scanner was in

last_pos = 0

output = []

while scanner.scan_until(/\[(.+?)\]/) # non-greedy matching so we

```

only swallow the first bracket

```
  # scanner[0] contains the string matched by the regexp

  # scanner[1] contains the value surrounded the parantheses in

```

the regexp

```
  # current position is right up to bracketed text

  current_pos = scanner.pos - 1 - scanner[0].length

  # the 'chunk' is the text from the last position the scanner

```

stopped at

```
  # up to the current position

  chunk = scanner.string[last_pos .. current_pos]

  output << chunk unless chunk.empty?

  # store the position the scanner is at for next time round the

```

loop

```
  last_pos = scanner.pos

  # extract the question answer thingies

  answers = scanner[1].split(',') # returns array

  # strip whitespace around each possible answer

  answers.each {|v| v.strip! } # works because strip! is

```

destructive

```
  # add answers array

  output << answers

end

# make sure we have any text after the last question/answer

last_chunk = scanner.string[last_pos..-1]

output << last_chunk unless last_chunk.empty?

output

```

end