require 'strscan'
StringScanner
StringScanner provides for lexical scanning operations on a String. Here is an example of its usage:
s = StringScanner.new('This is an example string')
s.eos? # -> false
p s.scan(/\w+/) # -> "This"
p s.scan(/\w+/) # -> nil
p s.scan(/\s+/) # -> " "
p s.scan(/\s+/) # -> nil
p s.scan(/\w+/) # -> "is"
s.eos? # -> false
p s.scan(/\s+/) # -> " "
p s.scan(/\w+/) # -> "an"
p s.scan(/\s+/) # -> " "
p s.scan(/\w+/) # -> "example"
p s.scan(/\s+/) # -> " "
p s.scan(/\w+/) # -> "string"
s.eos? # -> true
p s.scan(/\s+/) # -> nil
p s.scan(/\w+/) # -> nil
Scanning a string means remembering the position of a scan pointer, which is just an index. The point of scanning is to move forward a bit at a time, so matches are sought after the scan pointer; usually immediately after it.
Given the string “test string”, here are the pertinent scan pointer positions:
t e s t s t r i n g
0 1 2 ... 1
0
When you #scan for a pattern (a regular expression), the match must occur at the character after the scan pointer. If you use #scan_until, then the match can occur anywhere after the scan pointer. In both cases, the scan pointer moves just beyond the last character of the match, ready to scan again from the next character onwards. This is demonstrated by the example above.