BITCOUNT

The BITCOUNT command counts the number of set bits (population counting) in a string.

Syntax

BITCOUNT key [start] [end]

Parameters

• key - The key name
• start - Optional. Byte index to start counting (0-based). Can be negative to count from the end.
• end - Optional. Byte index to end counting (0-based). Can be negative to count from the end.

Return

Integer reply: the number of bits set to 1.

Examples

redis> SETBIT mykey 0 1
(integer) 0
redis> SETBIT mykey 1 1
(integer) 0
redis> SETBIT mykey 2 1
(integer) 0
redis> BITCOUNT mykey
(integer) 3
redis> BITCOUNT mykey 0 0
(integer) 3
redis> SET test_string "foobar"
OK
redis> BITCOUNT test_string 0 0
(integer) 4

Notes

• If no range is specified, counts bits in the entire string.
• If the range is out of bounds, returns 0.
• Negative indices count from the end of the string.
• The range is specified in bytes, not bits.