cmdcache

Simple utility to cache the output of the given commands. This springs from writing bash completion scripts which rely on custom cli tools which retrieve data from the cloud, causing every single tab-completion to result in a 800ms or more delay, rendering the completion unusable.

Setup

The easiest way to setup cmdcache is to use pip:

$ pip install cmdcache

Usage

Just prepend cmdcache before any shell commands in your shellscripts where you expect to use the stdout, and are OK with it being cached. Export the relevant CMDCACHE_* vars (see Caching section below) to control behavior.

Caching

Keys

cmdcache constructs a key from the given command, stripping out all non alphanumeric characters, then constructing a key with the following format:

$CMDCACHE_DIR/$CMDCACHE_PREFIX.{key}.cmdcache

The environment variable CMDCACHE_DIR defaults to /tmp and CMDCACHE_PREFIX defaults to default.

Storage

The cached output is stored in a file with the given key, and if its modification time is less than $CMDCACHE_MAX_AGE cmdcache will return the output of the file instead of running the command.

The environment variable CMDCACHE_MAX_AGE defaults to 10, which means 10 seconds.

Example

ses: ~ $ time cmdcache curl http://static.steinn.org/config.sample
THIS=is
A=sample
FILE=with
SOME=data

real	0m0.357s
user	0m0.066s
sys	0m0.048s

ses: ~ $ ls -ltr /tmp/|tail -1
-rw-r--r--  1 ses   wheel       37 Feb 23 13:16 default.curlhttpstaticsteinnorgconfigsample.cmdcache

If immediately re-run, the command is noticeably faster:

ses: ~ $ time cmdcache curl http://static.steinn.org/config.sample
THIS=is
A=sample
FILE=with
SOME=data

real	0m0.067s
user	0m0.042s
sys	0m0.021s

Thanks

Thanks to @ninjaaron for making https://github.com/ninjaaron/fast-entry_points without which this script would not be so useful when installed via pip.