From: Hugh Sasse <hgs@...>
Date: 2006-09-16T01:20:29+09:00
Subject: Re: Need help about Ruby with text file

On Sat, 16 Sep 2006, Oscar Lok wrote:

> By the way, may I know that is there any function like e.g. left(line, 
> 3), right(line, 2) and mid(line, 1, 4) to extract letter from a line, 
> please?
> e.g.
> mid(gghhii,3,2) return hh
> left(gghhii,3) return ggh
> right(gghhii,3) return hii

ri String#[] gives (for ruby-1.8.5): 

-------------------------------------------------------------- String#[]
     str[fixnum]                 => fixnum or nil
     str[fixnum, fixnum]         => new_str or nil
     str[range]                  => new_str or nil
     str[regexp]                 => new_str or nil
     str[regexp, fixnum]         => new_str or nil
     str[other_str]              => new_str or nil
     str.slice(fixnum)           => fixnum or nil
     str.slice(fixnum, fixnum)   => new_str or nil
     str.slice(range)            => new_str or nil
     str.slice(regexp)           => new_str or nil
     str.slice(regexp, fixnum)   => new_str or nil
     str.slice(other_str)        => new_str or nil
------------------------------------------------------------------------
     Element Reference---If passed a single +Fixnum+, returns the code
     of the character at that position. If passed two +Fixnum+ objects,
     returns a substring starting at the offset given by the first, and
     a length given by the second. If given a range, a substring
     containing characters at offsets given by the range is returned. In
     all three cases, if an offset is negative, it is counted from the
     end of _str_. Returns +nil+ if the initial offset falls outside the
     string, the length is negative, or the beginning of the range is
     greater than the end.

     If a +Regexp+ is supplied, the matching portion of _str_ is
     returned. If a numeric parameter follows the regular expression,
     that component of the +MatchData+ is returned instead. If a
     +String+ is given, that string is returned if it occurs in _str_.
     In both cases, +nil+ is returned if there is no match.

        a = "hello there"
        a[1]                   #=> 101
        a[1,3]                 #=> "ell"
        a[1..3]                #=> "ell"
        a[-3,2]                #=> "er"
        a[-4..-2]              #=> "her"
        a[12..-1]              #=> nil
        a[-2..-4]              #=> ""
        a[/[aeiou](.)\1/]      #=> "ell"
        a[/[aeiou](.)\1/, 0]   #=> "ell"
        a[/[aeiou](.)\1/, 1]   #=> "l"
        a[/[aeiou](.)\1/, 2]   #=> nil
        a["lo"]                #=> "lo"
        a["bye"]               #=> nil

Take the time to explore ri, which you should have on your system.
It is very good.

> 
> Thanks!
> Oscar
> 
        Hugh