irb> 'now is the time'[0...-4]
=> "now is the "

name = "my text"
x.times do name.chop! end

在控制台:

>name = "Nabucodonosor"
 => "Nabucodonosor" 
> 7.times do name.chop! end
 => 7 
> name
 => "Nabuco" 

使用正则表达式:

str = 'string'
n = 2  #to remove last n characters

str[/\A.{#{str.size-n}}/] #=> "stri"

irb> 'now is the time'[0...-4]
=> "now is the "

x = "my_test"
last_char = x.split('').last

查看slice()方法:

http://ruby-doc.org/core-2.5.0/String.html#method-i-slice