Ruby Sub Regular Expression

ruby-talk
1

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/.

2

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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3

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.

···

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.

5

Thank you Jim and Jesus

···

--
Posted via http://www.ruby-forum.com/.

6

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

···

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"

7

"lazy"

···

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)

8

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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