Ruby - 如何从字符串中选择一些字符

Question

我试图找到一个函数来选择例如字符串的前 100 个字符。在 PHP 中，存在 substr 函数

Ruby有类似的功能吗？

Answer 1

尝试 foo[0...100]，任何范围都可以。范围也可以为负值。 Ruby 文档对此进行了很好的解释。

Answer 2

使用 [] 运算符 (docs):

foo[0, 100]  # Get 100 characters starting at position 0
foo[0..99]   # Get all characters in index range 0 to 99 (inclusive!)
foo[0...100] # Get all characters in index range 0 to 100 (exclusive!)

更新为Ruby 2.7：无起始范围 现在就在这里（截至 2019 年 12 月 25 日），可能是“返回数组的第一个 xx”的规范答案：

foo[...100]  # Get all chars from the beginning up until the 100th (exclusive)

使用 .slice方法（docs）：

foo.slice(0, 100)  # Get 100 characters starting at position 0
foo.slice(0...100) # Behaves the same as operator [] 

为了完整性：

foo[0]         # Returns the indexed character, the first in this case
foo[-100, 100] # Get 100 characters starting at position -100
               # Negative indices are counted from the end of the string/array
               # Caution: Negative indices are 1-based, the last element is -1
foo[-100..-1]  # Get the last 100 characters in order
foo[-1..-100]  # Get the last 100 characters in reverse order
foo[-100...foo.length] # No index for one beyond last character

Ruby 2.6 更新 : 无尽的范围现在就在这里（如2018-12-25）！

foo[0..]      # Get all chars starting at the first. Identical to foo[0..-1]
foo[-100..]   # Get the last 100 characters

Answer 3

foo.first(100) 其中 foo 是一个字符串