# Regex question: this should be easy but doesn't work as I ex

**URL:** <https://www.ruby-forum.com/t/regex-question-this-should-be-easy-but-doesnt-work-as-i-ex/80002>\
**Category:** Ruby\
**Created:** [December 20, 2006, 8:11pm UTC](https://www.ruby-forum.com/t/regex-question-this-should-be-easy-but-doesnt-work-as-i-ex/80002 "2006-12-20T20:11:25Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 20, 2006, 8:11pm UTC](https://www.ruby-forum.com/t/regex-question-this-should-be-easy-but-doesnt-work-as-i-ex/80002/1 "2006-12-20T20:11:25Z")

</div>

Hi all,

-----Code------

re = [  
/(one).+?(three).+?(five)/,  
/(one).+?(three)?.+?(five)/,  
/(one).+?(three|).+?(five)/,  
/(one).+(three|).+?(five)/  
]

re.each\_with\_index do |r, idx|  
puts idx  
p “one two three four five”.scan®  
p “one two four five”.scan®  
end

-----Result---------

0  
[[“one”, “three”, “five”]]  
[]  
1  
[[“one”, nil, “five”]]  
[[“one”, nil, “five”]]  
2  
[[“one”, “”, “five”]]  
[[“one”, “”, “five”]]  
3  
[[“one”, “”, “five”]]  
[[“one”, “”, “five”]]

* * *

All regexes failed my expectation.

What I want is

“one two three four five” #=\> [[“one”, “three”, "five’]]  
“one two four five” #=\> [[“one”, nil, "five’]]

In short, in the string, “three” might or might not exist.  
What regex can match for both?

Thanks.

Sam

---

<div class="post-metadata">

**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 20, 2006, 8:55pm UTC](https://www.ruby-forum.com/t/regex-question-this-should-be-easy-but-doesnt-work-as-i-ex/80002/2 "2006-12-20T20:55:46Z")

</div>

Sam K. wrote:

> []
> 
> What regex can match for both?
> 
> Thanks.
> 
> Sam

/(one) two (?:(three) )?four (five)/

---

<div class="post-metadata">

**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 20, 2006, 9:07pm UTC](https://www.ruby-forum.com/t/regex-question-this-should-be-easy-but-doesnt-work-as-i-ex/80002/3 "2006-12-20T21:07:06Z")

</div>

Sam K. wrote:

> What I want is
> 
> “one two three four five” #=\> [[“one”, “three”, "five’]]  
> “one two four five” #=\> [[“one”, nil, "five’]]
> 
> In short, in the string, “three” might or might not exist.  
> What regex can match for both?

/one|three|five/ can. Although, its result is not exactly in the form  
you want:

> > “one two three four five”.scan /one|three|five/  
> > =\> [“one”, “three”, “five”]

> > “one two four five”.scan /one|three|five/  
> > =\> [“one”, “five”]

---

<div class="post-metadata">

**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 20, 2006, 11:10pm UTC](https://www.ruby-forum.com/t/regex-question-this-should-be-easy-but-doesnt-work-as-i-ex/80002/4 "2006-12-20T23:10:32Z")

</div>

Sam K. wrote:

> The image is sometimes missing.
> 
> In the example, let’s assume that “two” and “four” are arbiturary text.  
> So the text might be “…one…three…five” where “…” means some  
> arbiturary text.  
> If “three” is missing, it will be “…one…five…”.
> 
> Can you reconsider the problem please?
> 
> Sam

This is prolix, but it works:

a,b,c = ‘one’, ‘three’, ‘five’

[  
“one two three four five”,  
“one two four five”  
].each{|s|  
if s =~ /#{a} (.+ )?#{c}/  
if s =~ / #{b} /  
p [a,b,c]  
else  
p [a,nil,c]  
end  
end  
}

---

<div class="post-metadata">

**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 20, 2006, 10:12pm UTC](https://www.ruby-forum.com/t/regex-question-this-should-be-easy-but-doesnt-work-as-i-ex/80002/5 "2006-12-20T22:12:14Z")

</div>

Hi William,

William J. wrote:

> /(one) two (?:(three) )?four (five)/

I simplified the actual problem.  
I guess the simplification did not interpret my problem well.

I was parsing html source into price, image, description, etc.  
The image is sometimes missing.

In the example, let’s assume that “two” and “four” are arbiturary text.  
So the text might be “…one…three…five” where “…” means some  
arbiturary text.  
If “three” is missing, it will be “…one…five…”.

Can you reconsider the problem please?

Sam

---

<div class="post-metadata">

**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 21, 2006, 12:46am UTC](https://www.ruby-forum.com/t/regex-question-this-should-be-easy-but-doesnt-work-as-i-ex/80002/6 "2006-12-21T00:46:57Z")

</div>

On 12/20/06, Sam K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:  
[snip]

> “one two three four five” #=\> [[“one”, “three”, "five’]]  
> “one two four five” #=\> [[“one”, nil, "five’]]  
> [snip]

how about?

irb(main):001:0\> r = /(one) (?: (._?three) | ((?:.(?!\>three))_) ) _?  
(five)/x  
=\> /(one) (?: (._?three) | ((?:.(?!\>three))\*) ) \*? (five)/x  
irb(main):002:0\> “one two three four five”.scan(r)  
=\> [[“one”, " two three", " four ", “five”]]  
irb(main):003:0\> “one two four five”.scan(r)  
=\> [[“one”, nil, " two four ", “five”]]

---

<div class="post-metadata">

**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 21, 2006, 12:04am UTC](https://www.ruby-forum.com/t/regex-question-this-should-be-easy-but-doesnt-work-as-i-ex/80002/7 "2006-12-21T00:04:53Z")

</div>

[Sam K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid), 2006-12-20 20.10 CET]

> What I want is
> 
> “one two three four five” #=\> [[“one”, “three”, "five’]]  
> “one two four five” #=\> [[“one”, nil, "five’]]
> 
> In short, in the string, “three” might or might not exist.  
> What regex can match for both?

Hi. The problem is that you can very easily NOT match “three” even if  
it’s  
there. I mean, if you have  
/1.\*3?.\*5/ =~ ‘12345’

the engine can succeed matching the 1 at the beginning, the 5 at the  
end,  
and trying to match the 3 where the 4 is… and failing, but since it’s  
optional, the overall match succeeds.

I think you should try it in two steps: first, try to match with the 3;  
if  
that fails, without the “3”. Something like:

/(?:(1)._(3)|(1))._(5)/

(The ‘1’ will come either on the first or third array position, you’ll  
have  
to take care of that.)

Maybe there is a simpler solution, but it doesn’t come to my mind.

Good luck.

---

<div class="post-metadata">

**Author:** ![ssk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/82dd89/32.png) [@ssk](https://www.ruby-forum.com/u/ssk)\
**Post date:** [December 21, 2006, 2:15am UTC](https://www.ruby-forum.com/t/regex-question-this-should-be-easy-but-doesnt-work-as-i-ex/80002/8 "2006-12-21T02:15:06Z")

</div>

Hi Carlos,

Carlos wrote:

> /(?:(1)._(3)|(1))._(5)/
> 
> (The ‘1’ will come either on the first or third array position, you’ll have  
> to take care of that.)

Yes, you understand exactly what my problem is.  
Actually I guessed it as you said even if I couldn’t explain it as well  
as you did.  
The solution I found was using 2 regexes.  
First, I try to find a match assuming “three” is there.  
If it fails, I try to find a match without “three”.  
This solved my problem.  
But I wanted to know that if there’s a one-shot solution.

This is the actual problem, just in case someone wants to know.

html = \<\<END

##### 2004 Used

##### ``` <a name="210819526" href="210819526.html">BMW 325Ci Coupe</a><br /> </h5></td> <td class="mileage"> <span class="body20">38,604<br /></span><span ```

class=“body30”\>Mileage

```
                $24,995

        <br />
    </span>

        <span class="body30">Price</span>
    </td>

<td class="distanceFromZip">
    <div class="zip">
        <span class="body20">0 mi<br /></span><span

```

class=“body30”\>from ZIP

```
    <td class="productTileCell" rowspan="2" valign="top">

        <div class="srlProductContainer">

        </div>

    </td>

```

```
            <a href=210819526.html><img

```

src=“[http://images.autotrader.com/images/2006/10/16/210/819/1092478286.210819526.IM1.MAIN.60x45\_A.60x45.jpg](http://images.autotrader.com/images/2006/10/16/210/819/1092478286.210819526.IM1.MAIN.60x45_A.60x45.jpg)”  
border=“0” bordercolor=“#000000” width=“60” height=“45”\>&nbsp;

```
            <div class="body40" style="padding-bottom:3px">
                    <img

```

src=“[http://www.autotrader.com/img/fyc/icn\_camera\_17x17.gif](http://www.autotrader.com/img/fyc/icn_camera_17x17.gif)”  
alt=“Actual Photo Available” width=“17” height=“17” border=“0”  
/\>&nbsp;9 Photos

```
    <img src="http://www.autotrader.com/img/blank_dot.gif"

```

width=“60” height=“1” /\>

```
                <p class="color body20">Color - Mystic Blue

```

Metallic

```
            <p class="description">Dark Blue/Beige, Premium Pkg,

```

Xenon Light, Single Compact Disc, Dual Power Seats, Memory Seat, Still  
under Free BMW Maintenance and 4yr/50k Factory…

```
                <p class="vin">VIN WBABV13454JT20104</p>

            <div class="body40" style="padding-top:5px;"><a

```

name=“210819526” href=“210819526.html”\>View Car Details

```
    </div></td>
<td>&nbsp;</td>
<td valign="top" class="right body30">

    <p class="dealername">

            <a name="210819526" href="210819526.html">null</a>
            <br />

    </p>

    <br />

</td>

```

END

def parse\_row row  
m = row.scan(/.+?

##### (\d{4}) Used\</h5\>.+?

##### .+?\<a name="\d+" href="(\d+.html)"\>(.+?)\</a\>\<br /\>.+?\</h5\>.+?\<span class="body20"\>([0-9,]+)\<br /\>\</span\>\<span class="body30"\>Mileage\</span\>.+?($[0-9,]+).+?(http://[^"]+?.jpg).+?Color

- (.+?)\</p\>/m)  
if m[0].nil?  
m = row.scan(/.+?
##### (\d{4}) Used\</h5\>.+?

##### .+?\<a name="\d+" href="(\d+.html)"\>(.+?)\</a\>\<br /\>.+?\</h5\>.+?\<span class="body20"\>([0-9,]+)\<br /\>\</span\>\<span class="body30"\>Mileage\</span\>.+?($[0-9,]+).+?(http://[^"]+?.jpg)?.+?Color
- (.+?)\</p\>/m)  
end  
m[0]  
end

p parse\_row(html)

Sorry about the messy code.

Thanks.

Sam