Getting the Parts of a String You Want

2017-11-03 09:05:06

Problem

You want only certain pieces of a string.

Solution

To get a substring of a string, call its slice method, or use the array index operator (that is, call the [] method). Either method accepts a Range describing which characters to retrieve, or two Fixnum arguments: the index at which to start, and the length of the substring to be extracted.

s = 'My kingdom for a string!' s. slice(3,7) # => "kingdom" s[3,7] # => "kingdom" s[0,3] # => "My " s[11, 5] # => "for a" s[11, 17] # => "for a string!"

To get the first portion of a string that matches a regular expression, pass the regular expression into slice or []:

s[/.ing/] # => "king" s[/str.*/] # => "string!"

Discussion

To access a specific byte of a string as a Fixnum, pass only one argument (the zerobased index of the character) into String#slice or [] method. To access a specific byte as a single-character string, pass in its index and the number 1.

s.slice(3) # => 107 s[3] # => 107 107.chr # => "k" s.slice(3,1) # => "k" s[3,1] # => "k"

To count from the end of the string instead of the beginning, use negative indexes:

s.slice(-7,3) # => "str" s[-7,6] # => "string"

If the length of your proposed substring exceeds the length of the string, slice or [] will return the entire string after that point. This leads to a simple shortcut for getting the rightmost portion of a string:

s[15…s.length] # => "a string!"

Категории