Forum: Ruby Ruby Sub Regular Expression

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Dave R. (Guest)
on 2008-11-12 17:55
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.
Jim McKerchar (Guest)
on 2008-11-12 18:14
(Received via mailing list)
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
Jesús Gabriel y Galán (Guest)
on 2008-11-12 18:20
(Received via mailing list)
On Wed, Nov 12, 2008 at 4:52 PM, Dave R. <removed_email_address@domain.invalid>
wrote:
> => "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.
Dave R. (Guest)
on 2008-11-12 19:21
Thank you Jim and Jesus
Robert K. (Guest)
on 2008-11-12 22:31
(Received via mailing list)
On 12.11.2008 17:14, Jesús Gabriel y Galán wrote:
>> irb(main):018:0> b = a.sub(/\s-\s/, "")
> 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
Henrik -. (Guest)
on 2008-11-14 14:57
(Received via mailing list)
On Wed, Nov 12, 2008 at 5:11 PM, Jim McKerchar
<removed_email_address@domain.invalid> wrote:
> Hi. You missed out your non-greedy operator (if thats the right term)

"lazy"
Jim McKerchar (Guest)
on 2008-11-14 16:14
(Received via mailing list)
Thanks Henrik
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