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    <p>As its name implies, <code>SETBIT</code> allows you to perform bit operations - namely set a given bit to 0 or 1, at a given bit offset, for a given key.</p> <p>What is important to understand is that the result not always includes only printable characters. This is why Redis uses a <a href="https://github.com/antirez/redis/blob/320fa02/deps/hiredis/sds.c#L553-L576">custom function <code>sdscatrepr</code></a> to format the CLI output:</p> <blockquote> <p>Append to the sds string "s" an escaped string representation where all the non-printable characters (tested with isprint()) are turned into escapes in the form "\n\r\a...." or "\x".</p> </blockquote> <p>That being said let's start with a simple example. If you consider the hex number <code>0x7F</code> (= 127) its binary representation on 8-bit is:</p> <pre><code>pos: 0 1 2 3 4 5 6 7 bit: 0 1 1 1 1 1 1 1 ^ ^ | | MSB LSB </code></pre> <p>You can typically use <code>SETBIT</code> to store this value, keeping in mind that offset <code>0</code> is <code>MSB</code> and offset 7 is <code>LSB</code>:</p> <pre><code>redis&gt; SETBIT myval 0 0 (integer) 0 redis&gt; SETBIT myval 1 1 (integer) 0 redis&gt; SETBIT myval 2 1 (integer) 0 redis&gt; SETBIT myval 3 1 (integer) 0 redis&gt; SETBIT myval 4 1 (integer) 0 redis&gt; SETBIT myval 5 1 (integer) 0 redis&gt; SETBIT myval 6 1 (integer) 0 redis&gt; SETBIT myval 7 1 (integer) 0 </code></pre> <p>The get your value to inspect if:</p> <pre><code>redis&gt; GET myval "\x7f" </code></pre> <p>Now what happens with multi bytes? Let's say you want to store <code>0x52</code> (= 82) which corresponds to character <code>R</code> in ASCII. The 8-bit representation is <code>01010010</code> with bit positions <code>(8, 9, ..., 15)</code> since we want it to be stored right after the first value:</p> <pre><code>redis&gt; SETBIT myval 8 0 (integer) 0 redis&gt; SETBIT myval 9 1 (integer) 0 redis&gt; SETBIT myval 10 0 (integer) 0 redis&gt; SETBIT myval 11 1 (integer) 0 redis&gt; SETBIT myval 12 0 (integer) 0 redis&gt; SETBIT myval 13 0 (integer) 0 redis&gt; SETBIT myval 14 1 (integer) 0 redis&gt; SETBIT myval 15 0 (integer) 0 </code></pre> <p>And you get:</p> <pre><code>redis&gt; GET myval "\x7fR" </code></pre> <p>Here Redis CLI is able to represent the printable character <code>R</code>.</p> <blockquote> <p>When I store string value 1 and 7 into "mykey"</p> </blockquote> <p>It corresponds to <code>01000001</code> which is equal to 65 and <code>0x41</code> in hex. It corresponds to ASCII character <code>A</code>. So doing:</p> <pre><code>redis&gt; SETBIT mykey 1 1 (integer) 0 redis&gt; SETBIT mykey 7 1 (integer) 0 </code></pre> <p>Gives:</p> <pre><code>redis&gt; GET mykey "A" </code></pre> <blockquote> <p>how the getbit works inside redis?</p> </blockquote> <p>It simply returns the value of the bit at the given position. Here:</p> <pre><code>redis&gt; GETBIT mykey 1 (integer) 1 </code></pre> <p>But bit 0 has not been set (it is 0 by default) thus:</p> <pre><code>redis&gt; GETBIT mykey 0 (integer) 0 </code></pre>
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    1. POCan someone explain redis setbit command?
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    1. POCan someone explain redis setbit command?
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    1. COThanks for those information, I am wondering is it possible to get the string values(e.g. 1 and 7) by parsing ASCII characters(e.g. "A") which get from redis? I know redis doesn't provide such kind of functions. It will be cool if someone can give some hints.
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    2. COWhat do you mean by string values? (1 and 7 are bit offsets here). That said: you are free to manipulate Redis bulk replies the way you want (this is no more than a byte array) - see http://redis.io/topics/protocol.
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    3. COSorry, according to [redis document](http://redis.io/commands/setbit), _"Sets or clears the bit at offset in the string value stored at key."_ What I mean is that is it possible to get the offset from the string value. I am still trying to parse it in Erlang. e.g. If we do `setbit mykey 1 1` and `setbit mykey 2 1`, we get the output `<<96>>`; If we do `setbit mykey 1 1`, `setbit mykey 8 1` and `setbit mykey 16 1`, we get the output `<<64, 128, 128>>`. So what I am trying to do is parse the output and get the offsets out of it. (Sorry, the formats looked weird here.)
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