String.slice / []
A method that extracts a portion of a string. slice and [] (bracket notation) both perform the same operation.
Syntax
# Extract by specifying a start index and length. string.slice(start_index, length) string[start_index, length] # Extract using a range object. string[start..end] string[start...end] # Excludes the end index # Extract by specifying a substring. string[search_string]
Method List
| Notation | Description |
|---|---|
| str[n] | Returns the character at index n. A negative value counts from the end of the string. |
| str[n, len] | Extracts len characters starting from index n and returns them. |
| str[n..m] | Extracts the range from index n to m, inclusive. |
| str[n...m] | Extracts from index n up to, but not including, index m. |
| str[substr] | Returns the portion of the string that matches the substring. Returns nil if not found. |
Sample Code
text = "Hello, Ruby!" # Extract by index and length. puts text[0, 5] # Hello puts text[7, 4] # Ruby # Extract by range. puts text[0..4] # Hello puts text[0...5] # Hello (excludes the end index) # Use a negative index to count from the end. puts text[-5, 4] # Ruby puts text[-1] # ! (the last character) # Works the same way with Unicode text. greeting = "Good morning" puts greeting[0, 4] # Good puts greeting[5..] # morning (endless range, Ruby 2.6+) # Specify a substring. puts text["Ruby"] # Ruby puts text["Java"].inspect # nil # Extract year, month, and day from a date string. date = "2024-03-15" puts date[0, 4] # 2024 (year) puts date[5, 2] # 03 (month) puts date[8, 2] # 15 (day)
Notes
In Ruby, the [] notation is the most commonly used way to extract substrings. slice provides the same functionality in method form. If you specify an out-of-bounds index, nil may be returned, so always check the return value when using dynamic indexes.
Ruby 2.6 and later support endless ranges such as str[n..], which retrieves all characters from index n onward. You can also pass a regular expression as the argument (e.g., str[/\d+/]).
To split a string into an array, use split. To get the length of a string, use length / size.
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