exec¶
The exec definition-attribute can be used to obtain values from STDOUT when executing a shell command. All the usual parsers and selectors are available as they are with other source types.
Warning
It should be obvious, however, shell execution hazards and their appropriate precautions apply with this functionality.
Example - curl¶
For example using exec it is possible to set external values by calling curl
env-alias:
EXAMPLE:
exec: "curl -s https://ip-ranges.amazonaws.com/ip-ranges.json"
parser: "json"
selector: ".prefixes[1].ip_prefix"
This example is somewhat redundant because env-alias will perform a http-get request for any source definition that looks like a URL anyway.
Example - mkdir¶
This functionality can be useful in other ways too, such as making sure resources exist before loading an environment, for example create a path and skip setting the env variable.
Example - random string¶
Another example that invokes a shell-command to generate a 20 character random value, by default the source-type is text and the selector will take the first line so no further definition is required here.
If we expand this into long-form with its parser and selector, we'd get the same thing.
env-alias:
EXAMPLE:
exec: "head /dev/urandom | base64 - -w0 | tr -d "=/+" | head -c20"
parser: "text"
selector: 1
Example - host ip addr¶
Another example to obtain the first ip-address on the first interface of the host