# Problem modifying captured regexp results

**URL:** <https://www.ruby-forum.com/t/problem-modifying-captured-regexp-results/73017>\
**Category:** Ruby\
**Created:** [October 20, 2006, 6:00pm UTC](https://www.ruby-forum.com/t/problem-modifying-captured-regexp-results/73017 "2006-10-20T18:00:23Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [October 20, 2006, 6:00pm UTC](https://www.ruby-forum.com/t/problem-modifying-captured-regexp-results/73017/1 "2006-10-20T18:00:23Z")

</div>

Hello,

I’m using ruby to automatically generate Fortran95 code and I’m using a  
regular expression  
to parse the following type of definition line:

REAL(fp), DIMENSION(Dim1,Dim2) :: Arr2 ! Description of Arr2

The regexp I’m using works fine and I build a array of hashes for each  
definition, i.e.

```
 if line =~ componentRegexp
   # We have matched an array component definition
  arrayList<<{"type"=>$1,
              "param"=>$2,
              "dimlist"=>$3,
              "name"=>$4,
              "description"=>$5}
   puts(arrayList.last.inspect)
 else
   # No match, so raise an error
   raise StandardError, "Invalid array definition, #{$~}"
 end

```

which works fine. The inspect o/p gives me:

{“name”=\>“Arr2”, “type”=\>“REAL”, “description”=\>“Description of Arr2”,  
“param”=\>“fp”,  
“dimlist”=\>“Dim1,Dim2”}

However, what I want to do is modify the dimlist in the hash so it is a  
string array  
“dimlist”=\>[“Dim1”,“Dim2”]  
rather than a single string,  
“dimlist”=\>“Dim1,Dim2”

Because the number of dimensions in the dimlist can vary from 1 to 7,  
rather than do the  
splitting in the regexp, I tried doing it in the arrayList concatenation  
using the split  
method like so,

```
   arrayList<<{"type"=>$1,
               "param"=>$2,
               "dimlist"=>$3.split(/\s*,\s*/), # <--- split dimlist 

```

on “,”  
“name”=\>$4,  
“description”=\>$5}

but I’ve found that the above operation on the $3 captured result  
appears to “wipe” the  
subsequent entries $4 (name) and $5 (description). For example, the  
output of  
puts(arrayList.last.inspect)  
on the above gives me,

{“name”=\>nil, “type”=\>“REAL”, “description”=\>nil, “param”=\>“fp”,  
“dimlist”=\>[“Dim1”, “Dim2”]}

Note that the “dimlist” is how I want it, but “name” and “description”  
entries are now nil.

So can someone elaborate on why the above split operation on captured  
regexp results seems  
to bugger up the other captured results? Does this issue extend to _any_  
operation on  
captured regexp results?

I’ve looked through the pickaxe and cookbook, but no information on this  
was immediately  
apparent.

Thanks for any info.

cheers,

paulv

---

<div class="post-metadata">

**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [October 20, 2006, 6:24pm UTC](https://www.ruby-forum.com/t/problem-modifying-captured-regexp-results/73017/2 "2006-10-20T18:24:32Z")

</div>

Paul van Delst schrieb:

> but I’ve found that the above operation on the $3 captured result  
> appears to “wipe” the subsequent entries $4 (name) and $5 (description).

Paul, the problem is that #split with a Regexp internally executes some  
Regexp matches which change $1, $2 etc. You have to capture the results  
of the first match before executing the split.

Regards,  
Pit

---

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**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [October 20, 2006, 7:06pm UTC](https://www.ruby-forum.com/t/problem-modifying-captured-regexp-results/73017/3 "2006-10-20T19:06:43Z")

</div>

Pit C. wrote:

> > but I’ve found that the above operation on the $3 captured result  
> > appears to “wipe” the subsequent entries $4 (name) and $5 (description).
> 
> Paul, the problem is that #split with a Regexp internally executes some  
> Regexp matches which change $1, $2 etc. You have to capture the results  
> of the first match before executing the split.

Aha! That is the answer to the question (see my other post).

Bewdy. Thanks Pit and Gavin.

cheers,

paulv

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<div class="post-metadata">

**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [October 21, 2006, 9:22pm UTC](https://www.ruby-forum.com/t/problem-modifying-captured-regexp-results/73017/4 "2006-10-21T21:22:36Z")

</div>

On 10/20/06, Pit C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > but I’ve found that the above operation on the $3 captured result  
> > appears to “wipe” the subsequent entries $4 (name) and $5 (description).
> 
> Paul, the problem is that #split with a Regexp internally executes some  
> Regexp matches which change $1, $2 etc. You have to capture the results  
> of the first match before executing the split.

In this case, it’s really easy: just reorder the lines so that the one  
containing split will be the last (hash changes the order anyway):

```
   arrayList<<{"type"=>$1,
               "param"=>$2,
               "name"=>$4,
               "description"=>$5,
               "dimlist"=>$3.split(/\s*,\s*/)}

```

This will work fine as in the moment split messes up those $x, you  
don’t need them any more. Obviously this would not work if there were  
more splits.