how to find the position of each match within a string

[Li Chen]

Hi all,

I have a small script to find a match. If a match is found I need to
print its position within the string. I try the String#index but it only
returns the first match. Any idea?

Thanks,

Li

C:\Documents and Settings\chen73\My Documents\Ruby\bin>irb
irb(main):001:0> "ello-hello".scan('e') do |match|
irb(main):002:1* p "ello-hello".index(match)
irb(main):003:1> end
0
0
=> "ello-hello"
irb(main):004:0>

 

[Albert Schlef]

You can examine the $~ global MatchData object, in a couple of ways:

irb(main):003:0> "ello-hello".scan('e') do |match|
irb(main):004:1* p $~.pre_match.size
irb(main):005:1> end
0
6

Interesting. Does that mean that String#scan() converts a String
argument to RegExp?

 

[Rados³aw Bu³at]

Interesting. Does that mean that String#scan() converts a String
argument to RegExp?

Yes it does, even if it search fixed-size string.


--=20
Pozdrawiam

Rados=B3aw Bu=B3at
http://radarek.jogger.pl - m=F3j blog

 

[Albert Schlef]

Yes it does, even if it search fixed-size string.

I'm shocked. Why does it do this? (this conversion)

And doesn't this mean that #scan is less efficient than it could have
been? Isn't matching regexps slower than matching plain strings?

 

[Li Chen]

You can examine the $~ global MatchData object, in a couple of ways:

irb(main):003:0> "ello-hello".scan('e') do |match|
irb(main):004:1* p $~.pre_match.size
irb(main):005:1> end
0
6
=> "ello-hello"
irb(main):006:0> "ello-hello".scan('e') do |match|
irb(main):007:1* p $~.offset(0)[0]
irb(main):008:1> end
0
6
=> "ello-hello

Hi David,

Thanks.

I go back and read the chapter about MatchData. And it helps me a lot.

Li