redis-cli: print (nil) or (empty list or set) to stderr

[GoogleCodeExporter]

redis-cli sends values to stdout when there actually aren't any, such as 
"(nil)" or "(empty list or set)":

$ redis-cli lpush samplelist value1
(integer) 1

$ redis-cli lpush samplelist value2
(integer) 2

$ redis-cli lpush samplelist value3
(integer) 3

$ for i in `redis-cli lrange "samplelist" 0 100`; do echo "value: ($i)"; done
value: (value3)
value: (value2)
value: (value1)

$ for i in `redis-cli lrange "emptylist" 0 100`; do echo "value: ($i)"; done
value: ((empty)
value: (list)
value: (or)
value: (set))

so here are two ideas to make this feasible:

1) output the (nil), (empty list or set), etc to stderr instead of stdout

2) set status code to zero if no error, no values not found=1, 2-255 for 
errors... this permits things like:
   $(redis-cli get something) || redis-cli set something else;

(see also "redis-cli should set error status on nil key",
http://code.google.com/p/redis/issues/detail?id=447 )

Original issue reported on code.google.com by jamiesonbecker@gmail.com on 24 Mar 2011 at 2:00

[GoogleCodeExporter]

Also, just noticed that values echoed to STDOUT do not properly handle EOL. 
redis-cli does not escape even basic things like newlines upon 
storage/retrieval and really shouldn't be used to retrieve any sort of 
untrusted data. I can't really access redis from short-lived processes unless I 
want to (carefully) write them in C because most scripting languages take a 
while to start up (sometimesy 10x the startup latency compared a bash script 
once the redis lib is included.)

here's an example:

$ redis-cli lpush samplelist "value with space"
(integer) 4
for i in `redis-cli lrange "samplelist" 0 100`; do echo "value: ($i)"; done
value: (value)
value: (with)
value: (space)
value: (value3)
value: (value2)
value: (value1)

Ideally, each value would have an EOL (\n) between, and \n's would be escaped 
on input. This is really a separate but closely related bug, so let me know if 
you want me to open a second bug report for this.

Original comment by jamiesonbecker@gmail.com on 24 Mar 2011 at 2:17

[GoogleCodeExporter]

Output of redis-cli being separated by spaces is not a redis-cli issue, but 
rather a shell one. If you try running the loop against "echo value with 
spaces", you'll see the exact same thing. Bash (not sure about other shells) 
use whitespace as a field separator by default, so will always see a single 
line with strings separated by spaces as multiple elements. You can use the IFS 
variable to override the character bash splits on.

By default, redis-cli delimits every element in a multi-bulk with an EOL, but 
this can be customized by passing the -d option to redis-cli (also see --help, 
v2.2). For instance, delimiting by the NUL character and piping the output to 
xargs -0 can be very useful.

Printing the special values (nil) and (empty list or set) to stderr sounds like 
a good plan. I don't think, however, that changing the exit status is a good 
idea, because that is currently used to signal not being able to connect. When 
the special values are printed to stderr, you can simply test for empty output 
on stdout to know if there was a reply or not. Leaving this issue open for 
printing specials to stderr.

Original comment by pcnoordh...@gmail.com on 24 Mar 2011 at 8:36

• Changed title: redis-cli: print (nil) or (empty list or set) to stderr
• Changed state: Accepted
• Added labels: Type-Enhancement
• Removed labels: Type-Defect