Ruby Sub Regular Expression
 

Hello! I have a string: "Hello - 1 - World"

irb(main):017:0> a = "Hello - 1 - World"
=> "Hello - 1 - World"

I want to chop off the "Hello - " part. Hello could be any word, so I
want to match it generically.
To match the first minus I do this:

irb(main):018:0> b = a.sub(/\s-\s/, "")
=> "Hello1 - World"

Good! Now to get rid of the first word I try this:

irb(main):019:0> c = a.sub(/.*\s-\s/, "")
=> "World"

Bad! It matched to the second minus! Why does sub do this? I thought
it was supposed to match the first occurrence only.
--
Posted via http://www.ruby-forum.com/.

Re: Ruby Sub Regular Expression
 

Hi. You missed out your non-greedy operator (if thats the right term) in
your regex.

Try:

a = "Hello - 1 - World"

c = a.sub(/.*?\s-\s/, "")

irb(main):004:0> c = a.sub(/.*?\s-\s/, "")
=> "1 - World"


Hope that helps
Jim









Dave Roberts wrote:
> Hello! I have a string: "Hello - 1 - World"
>
> irb(main):017:0> a = "Hello - 1 - World"
> => "Hello - 1 - World"
>
> I want to chop off the "Hello - " part. Hello could be any word, so I
> want to match it generically.
> To match the first minus I do this:
>
> irb(main):018:0> b = a.sub(/\s-\s/, "")
> => "Hello1 - World"
>
> Good! Now to get rid of the first word I try this:
>
> irb(main):019:0> c = a.sub(/.*\s-\s/, "")
> => "World"
>
> Bad! It matched to the second minus! Why does sub do this? I thought
> it was supposed to match the first occurrence only.
>
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>
>
> No virus found in this incoming message.
> Checked by AVG - http://www.avg.com
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>
>

Re: Ruby Sub Regular Expression
 

On Wed, Nov 12, 2008 at 4:52 PM, Dave Roberts <dave.a.roberts@gmail.com> wrote:
> Hello! I have a string: "Hello - 1 - World"
>
> irb(main):017:0> a = "Hello - 1 - World"
> => "Hello - 1 - World"
>
> I want to chop off the "Hello - " part. Hello could be any word, so I
> want to match it generically.
> To match the first minus I do this:
>
> irb(main):018:0> b = a.sub(/\s-\s/, "")
> => "Hello1 - World"
>
> Good! Now to get rid of the first word I try this:
>
> irb(main):019:0> c = a.sub(/.*\s-\s/, "")
> => "World"
>
> Bad! It matched to the second minus! Why does sub do this? I thought
> it was supposed to match the first occurrence only.

Because * by default is greedy, so it tries to match as much as it can.
Try this:

irb(main):002:0> c = a.sub(/.*?\s-\s/, "")
=> "1 - World"

Jesus.

Re: Ruby Sub Regular Expression
 

Re: Ruby Sub Regular Expression
 

Thank you Jim and Jesus
--
Posted via http://www.ruby-forum.com/.

Re: Ruby Sub Regular Expression
 

On 12.11.2008 17:14, Jesús Gabriel y Galán wrote:
> On Wed, Nov 12, 2008 at 4:52 PM, Dave Roberts <dave.a.roberts@gmail.com> wrote:
>> Hello! I have a string: "Hello - 1 - World"
>>
>> irb(main):017:0> a = "Hello - 1 - World"
>> => "Hello - 1 - World"
>>
>> I want to chop off the "Hello - " part. Hello could be any word, so I
>> want to match it generically.
>> To match the first minus I do this:
>>
>> irb(main):018:0> b = a.sub(/\s-\s/, "")
>> => "Hello1 - World"
>>
>> Good! Now to get rid of the first word I try this:
>>
>> irb(main):019:0> c = a.sub(/.*\s-\s/, "")
>> => "World"
>>
>> Bad! It matched to the second minus! Why does sub do this? I thought
>> it was supposed to match the first occurrence only.
>
> Because * by default is greedy, so it tries to match as much as it can.
> Try this:
>
> irb(main):002:0> c = a.sub(/.*?\s-\s/, "")
> => "1 - World"

Other variants would be

irb(main):001:0> a = "Hello - 1 - World"
=> "Hello - 1 - World"
irb(main):002:0> a[/\d+\s+-.*/]
=> "1 - World"
irb(main):003:0> a.sub /^\S+\s+-\s+/, ''
=> "1 - World"
irb(main):004:0> a.sub /^\w+\s+-\s+/, ''
=> "1 - World"
irb(main):005:0>

Cheers

robert

Re: Ruby Sub Regular Expression
 

On Wed, Nov 12, 2008 at 5:11 PM, Jim McKerchar
<jim.mckerchar@btinternet.com> wrote:
> Hi. You missed out your non-greedy operator (if thats the right term)

"lazy"

Re: Ruby Sub Regular Expression
 

Thanks Henrik

Henrik Nyh wrote:
> On Wed, Nov 12, 2008 at 5:11 PM, Jim McKerchar
> <jim.mckerchar@btinternet.com> wrote:
>
>> Hi. You missed out your non-greedy operator (if thats the right term)
>>
>
> "lazy"
>
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>
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