# Regexp Parsing -- What's the right way?

**URL:** <https://www.ruby-forum.com/t/regexp-parsing-whats-the-right-way/102454>\
**Category:** Ruby\
**Created:** [August 15, 2006, 2:17pm UTC](https://www.ruby-forum.com/t/regexp-parsing-whats-the-right-way/102454 "2006-08-15T14:17:45Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [August 15, 2006, 2:17pm UTC](https://www.ruby-forum.com/t/regexp-parsing-whats-the-right-way/102454/1 "2006-08-15T14:17:45Z")

</div>

Greetings,

I’m trying to parse the following line:

“00608 P 135 001 LEC Tu 2-5P 210 WHEELER Information Tech and Soceity 3  
LAGUERRE”

i’ve constructed the following regexp:  
/(\d{5}).(\D\s\w{2,4}).(\d{1,4}\s\D{3}).(\D{1,4}\s\d+)._(\d{1,4}\s\D{1,9}).(\w+)._(\d?)._(\w{1,14})._/

with a input file i’ve successfully produced the following output:  
control# 00608 ---- correct  
course#: P 135 ---- correct  
section#: 001 LEC ---- correct  
day-hour#: Tu 2 ---- missing '-5P  
room#: 3 LAGUERRE, ---- should be 210 WHEELER  
course-name#: M — IT and Soceity  
credits#: — should be 3  
prof#: 5 — should be LAGUERRE

i’m a novice to ruby and regexp. i would like to know if i’m taking the  
right approach.  
i’ll eventually nail it but any hints or suggestions would be useful.

appreciate the help.

---

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [August 15, 2006, 2:17pm UTC](https://www.ruby-forum.com/t/regexp-parsing-whats-the-right-way/102454/2 "2006-08-15T14:17:48Z")

</div>

removed\_email\_address@domain.invalid wrote:

> with a input file i’ve successfully produced the following output:  
> right approach.  
> i’ll eventually nail it but any hints or suggestions would be useful.
> 
> appreciate the help.

I would go with split in this case:

t = “00608 P 135 001 LEC Tu 2-5P 210 WHEELER Information Tech and  
Soceity 3  
LAGUERRE”  
a = t.split  
#strip from the beginning  
control = a.shift  
course = a.shift + ’ ’ + a.shift  
section = a.shift + ’ ’ + a.shift  
hour = a.shift + ’ ’ + a.shift  
room = a.shift + ’ ’ + a.shift  
#strip from behind  
prof = a.pop  
credits = a.pop  
#the rest is the name  
coursen = a.join(’ ')

puts “control: #{control}”  
puts “course: #{course}”  
puts “section: #{section}”  
puts “hour: #{hour}”  
puts “room: #{room}”  
puts “coursen: #{coursen}”  
puts “credits: #{credits}”  
puts “prof: #{prof}”

cheers

Simon

---

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [August 15, 2006, 2:17pm UTC](https://www.ruby-forum.com/t/regexp-parsing-whats-the-right-way/102454/3 "2006-08-15T14:17:52Z")

</div>

On 8/12/06, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Greetings,
> 
> I’m trying to parse the following line:  
> …

Hi,

although in this case I’d prefer the array.split solution here’s how  
it can be done in case you really need regex:  
These are incremental versions of the regex, and a test to check them.  
Save to file and enjoy!

Jano

#!/usr/bin/ruby  
require ‘test/unit’

DATA = “00608 P 135 001 LEC Tu 2-5P 210 WHEELER IT and Society 3  
LAGUERRE”

REGEX1 =  
/(\d{5}).(\D\s\w{2,4}).(\d{1,4}\s\D{3}).(\D{1,4}\s\d+)._(\d{1,4}\s\D{1,9}).(\w+)._(\d?)._(\w{1,14})._/

# add /x and # comments,

REGEX2 = /  
(\d{5}). # control  
(\D\s\w{2,4}). # course  
(\d{1,4}\s\D{3}). # section  
(\D{1,4}\s\d+).\* # day-hour  
(\d{1,4}\s\D{1,9}). # room  
(\w+).\* # course-name  
(\d?).\* # credits  
(\w{1,14}).\* # professor  
/x

# now we’ll fix the day-hour: add -\d[AP] - that will match a slash,

# a digit and either ‘A’ or ‘P’

# and fix for the room: \D{1,9} replace with \w+

REGEX3 = /  
(\d{5}). # control  
(\D\s\w{2,4}). # course  
(\d{1,4}\s\D{3}). # section  
(\D{1,4}\s\d±\d[AP]). # day-hour  
(\d{1,4}\s\w+). # room  
(\w+).\* # course-name  
(\d?).\* # credits  
(\w{1,14}).\* # professor  
/x

# To fix course name, the previous tricks aren’t enough –

# there are many words, with different length. So what we’ll do?

# We’ll parse the things at the end: credits and professor

# 

# To see the results, temporarily comment out the lines

# that checks the course name and credits in the test

# and run it with REGEX3.

# 

# To fix the professor, we’ll say that it’s tha last word on the line:

# notice the \s+ before the professor group - there has to be something

# fixed that separates the name from the rest - .\* won’t do it.

REGEX4 = /  
(\d{5}). # control  
(\D\s\w{2,4}). # course  
(\d{1,4}\s\D{3}). # section  
(\D{1,4}\s\d±\d[AP]). # day-hour  
(\d{1,4}\s\w+). # room  
(\w+).\* # course-name  
(\d?)\s+ # credits  
(\w+)\s\*$ # professor  
/x

# Now we can try the rest two pieces: uncomment credits and

# we’ll see that they are already ok, so uncomment course name as well.

# 

# Only the first word appears. So we’ll move .\* inside the parentheses

# and add a separating \s+

# 

# Finally some small touches:

# replace separating . with \s+

REGEX5 = /  
(\d{5})\s+ # control  
(\D\s\w{2,4})\s+ # course  
(\d{1,4}\s\D{3})\s+ # section  
(\D{1,4}\s\d±\d[AP])\s+# day-hour  
(\d{1,4}\s\w+)\s+ # room  
(._)\s+ # course-name  
(\d+)\s+ # credits  
(\w+)\s_$ # professor  
/x

class TestRegex \< Test::Unit::TestCase  
def test\_regex  
assert DATA =~ REGEX1 # \<— change number here  
assert\_equal “00608”, $1  
assert\_equal “P 135”, $2  
assert\_equal “001 LEC”, $3  
assert\_equal “Tu 2-5P”, $4  
assert\_equal “210 WHEELER”, $5  
assert\_equal “IT and Society”, $6  
assert\_equal “3”, $7  
assert\_equal “LAGUERRE”, $8  
end  
end

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [August 15, 2006, 2:17pm UTC](https://www.ruby-forum.com/t/regexp-parsing-whats-the-right-way/102454/4 "2006-08-15T14:17:54Z")

</div>

removed\_email\_address@domain.invalid wrote:

> with a input file i’ve successfully produced the following output:  
> the right approach.  
> i’ll eventually nail it but any hints or suggestions would be useful.
> 
> appreciate the help.

Looks pretty ok to me apart from that I’d use \s instead of . to parse  
white  
space separating entries.

```
robert
```

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [August 15, 2006, 2:18pm UTC](https://www.ruby-forum.com/t/regexp-parsing-whats-the-right-way/102454/5 "2006-08-15T14:18:19Z")

</div>

Hi,

I worked on the regexp some more before I saw everyone’s response.  
I was able to extract all parts except for the day hour. I was treating

- as “-” and the literals A as “A” and P as “P” so I didn’t hit any  
matches.

I see you created line breaks with each component of the REGEXP. I will  
follow that convention from now on.

I also now understand the difference between .\* and \s+ as many of you  
have pointed out.

I’m new to ruby as well and will continue to expreriment with it some  
more.

Thanks for your responses.  
[sukhchander]

---

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [August 15, 2006, 2:18pm UTC](https://www.ruby-forum.com/t/regexp-parsing-whats-the-right-way/102454/6 "2006-08-15T14:18:19Z")

</div>

Hi Simon,

That’s pretty cool.  
I was looking for a utility similar to Java’s StringTokenizer. You just  
pointed it out.  
Ruby has so many things built in. It’s very comprehensive.

For larger regexp I assume you prefer the split/tokenize method?

I went with the Regexp approach because it occurred to me first.

Thanks.  
[sukhchander]

---

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [August 15, 2006, 2:18pm UTC](https://www.ruby-forum.com/t/regexp-parsing-whats-the-right-way/102454/7 "2006-08-15T14:18:24Z")

</div>

sukhchander wrote:

> Hi Simon,
> 
> That’s pretty cool.  
> I was looking for a utility similar to Java’s StringTokenizer. You just  
> pointed it out.  
> Ruby has so many things built in. It’s very comprehensive.
> 
> For larger regexp I assume you prefer the split/tokenize method?
> 
> I went with the Regexp approach because it occurred to me first.

Personally I’d stick with the regexp approach as it has these  
advantages:

- probably faster because you don’t have to split and then combine  
again

- more precise with regard to matching, i.e. you can better define  
where to match plus you get the info whether the input string is  
properly formatted

Btw, if you want to dive into regexp I can recommend “Mastering Regular  
Expressions”. It’s probably best to first get some basic knowledge of  
RX but if you want to know how to build efficient RX etc. then that book  
is definitive a great help. Ah, I get carried away…

Then there’s also tool programs that help in understanding RX visually.  
RegexBuddy and Regex-Coach.

Kind regards

```
robert
```