From: Devin Mullins <twifkak@...>
Date: 2005-09-24T10:44:03+09:00
Subject: Re: trimming strings

Florian Gro� wrote:

> jotto wrote:
>
>> I want to trim the string for the text that comes with each entry in
>> the database. Ideally I want to trim it where it first finds <br />. I
>> imagine I use a loop to count how many characters I get to before it
>> finds <br />? Then I use some function (a function I can't find) that
>> trims the string to the desired amount of characters.
>
> Try this: str[0 ... str.index("<br />")]
>
> You probably do it more efficiently with Regexps, but that involves 
> getting the multi-line flag right.

Devin's experiments with figuring this stuff out:

C:\Documents and Settings\dlm>ri Regexp
---------------------------------------------------------- Class: Regexp
     Document-class: Regexp

     A +Regexp+ holds a regular expression, used to match a pattern
     against strings. Regexps are created using the +/.../+ and
     +%r{...}+ literals, and by the +Regexp::new+ constructor.

------------------------------------------------------------------------


Class methods:
--------------
     compile, escape, last_match, new, quote, union


Instance methods:
-----------------
     ==, ===, =~, casefold?, eql?, hash, initialize_copy, inspect,
     kcode, match, options, source, to_s, ~

C:\Documents and Settings\dlm>ri Regexp.new
------------------------------------------------------------ Regexp::new
     Regexp.new(string [, options [, lang]])       => regexp
     Regexp.new(regexp)                            => regexp
     Regexp.compile(string [, options [, lang]])   => regexp
     Regexp.compile(regexp)                        => regexp
------------------------------------------------------------------------
     Constructs a new regular expression from _pattern_, which can be
     either a +String+ or a +Regexp+ (in which case that regexp's
     options are propagated, and new options may not be specified (a
     change as of Ruby 1.8). If _options_ is a +Fixnum+, it should be
     one or more of the constants +Regexp::EXTENDED+,
     +Regexp::IGNORECASE+, and +Regexp::POSIXLINE+, _or_-ed together.
     Otherwise, if _options_ is not +nil+, the regexp will be case
     insensitive. The _lang_ parameter enables multibyte support for the
     regexp: `n', `N' = none, `e', `E' = EUC, `s', `S' = SJIS, `u', `U'
     = UTF-8.

        r1 = Regexp.new('^a-z+:\s+\w+')           #=> /^a-z+:\s+\w+/
        r2 = Regexp.new('cat', true)               #=> /cat/i
        r3 = Regexp.new('dog', Regexp::EXTENDED)   #=> /dog/x
        r4 = Regexp.new(r2)                        #=> /cat/i


C:\Documents and Settings\dlm>irb
irb(main):001:0> "hello\nfun" =~ /o.*un/
=> nil
irb(main):002:0> "hello\nfun" =~ /o.*un/m
=> 4
irb(main):003:0> "This is some text
irb(main):004:0" I am typing<br />Lookee
irb(main):005:0" here!<br />"[0 ... %r{<br />}]
ArgumentError: bad value for range
        from (irb):5
irb(main):006:0> "This is some text
irb(main):007:0" I am typing<br />Lookee
irb(main):008:0" here!<br />"[0, %r{<br />}]
TypeError: cannot convert Regexp into Integer
        from (irb):8:in `[]'
        from (irb):8
irb(main):009:0>
C:\Documents and Settings\dlm>ri "String#[]"
-------------------------------------------------------------- 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


C:\Documents and Settings\dlm>\irb
'\irb' is not recognized as an internal or external command,
operable program or batch file.

C:\Documents and Settings\dlm>irb
irb(main):001:0> "This is some text
irb(main):002:0" I am typing<br />Lookee
irb(main):003:0" here"[%r{(.*?)<br />},0]
=> "I am typing<br />"
irb(main):004:0> "This is some text
irb(main):005:0" I am typing<br />Lookee
irb(main):006:0" here"[%r{(.*?)<br />}m,0]
=> "This is some text\nI am typing<br />"
irb(main):007:0> "This is some text
irb(main):008:0" I am typing<br />Lookee
irb(main):009:0" here"[%r{(.*?)<br />}m,1]
=> "This is some text\nI am typing"

The End.

Devin