SubstrCommand
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Time complexity: O(start+n) (with start being the start index and n the total length of the requested range). Note that the lookup part of this command is O(1) so for small strings this is actually an O(1) command.Warning: this command was renamed into GETRANGE. SUBSTR will be taken as an alias until the next major release of Redis.
Return a subset of the string from offset start to offset end(both offsets are inclusive).Negative offsets can be used in order to provide an offset starting fromthe end of the string. So -1 means the last char, -2 the penultimate andso forth.
The function handles out of range requests without raising an error, butjust limiting the resulting range to the actual length of the string.
Bulk reply
redis> set s "This is a string"
OK
redis> substr s 0 3
"This"
redis> substr s -3 -1
"ing"
redis> substr s 0 -1
"This is a string"
redis> substr s 9 100000
" string"