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SUBSTR (Deprecated)

This command is deprecated and has been replaced by the GETRANGE command. It was used to return a substring of the string stored at a key, determined by the specified start and end offsets.

Syntax​

SUBSTR key start end

Parameters​

  • key: The name of the key whose string you want to retrieve a substring from.
  • start: The zero-based starting index of the substring. Negative values can be used to specify offsets from the end of the string.
  • end: The zero-based ending index of the substring (inclusive). Negative values can be used to specify offsets from the end of the string.

Details​

  • Available since: 1.0.0
  • Time complexity: O(N) where N is the length of the returned substring.
  • ACL categories: @read, @string, @slow

The SUBSTR command was used to retrieve a substring of the string stored at key, as specified by the start and end parameters. The substring includes both the start and end offsets. If the key does not exist, SUBSTR returns an empty string.

Indexing​

  • 0: The first character in the string.
  • -1: The last character in the string.
  • -2: The second last character, and so on.

Examples​

Basic Usage​

Assume we have a key called mykey with the value "Hello, World!":

SET mykey "Hello, World!"

To retrieve the substring from index 0 to 4:

SUBSTR mykey 0 4

This will return:

"Hello"

Using Negative Indices​

To retrieve the substring from the last 6 characters of the string:

SUBSTR mykey -6 -1

This will return:

"World!"

Edge Cases​

  • If the key does not exist, SUBSTR returns an empty string.
  • If the key exists but is not a string, an error is returned.
  • If start is greater than end, SUBSTR returns an empty string.
  • If the specified range exceeds the length of the string, SUBSTR returns the available substring.

RESP2/RESP3 Reply​

  • Bulk string reply: the requested substring, or an empty string if the key does not exist or the range is invalid.