Set a default value for a variable if ENV is empty

[Loren Gordon]

Hello,

Is it possible to set a default value for a variable in a packer template, but override that default with an ENV? I'm thinking of something equivalent to the shell syntax, `var="${ENV:-default}"`. I've looked, but can't seem to find a way to do this...

Thanks,

-Loren

[Brett Russ]

On Tuesday, April 19, 2016 at 7:03:48 PM UTC-4, Loren Gordon wrote:

Hello,

Is it possible to set a default value for a variable in a packer template, but override that default with an ENV? I'm thinking of something equivalent to the shell syntax, `var="${ENV:-default}"`. I've looked, but can't seem to find a way to do this...

Could you move the entire problem to shell?

DFLT={{user `dflt`}}
VAR=${ENV:-DFLT}

then use the $VAR shell var? 

[Loren Gordon]

Interesting, thanks! I'll try it. It would be more elegant if it were natively supported in packer, but this might be good enough.

-Loren

[Alvaro Miranda Aguilera]

Hello,

If you define

key=value in the variables block, thats the default

then can be overrided with

packer build -var "key=newvalue" template.json

or

packer build -var "key=${var}" template.json

is this what you are after?

if not, can you explain more?

alvaro.

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[Loren Gordon]

No, not quite. What I'm looking to do is define a default value, which may be overridden by an ENV, which may be overridden by a command line variable.

For example, I can assign a default value to a packer variable, "myvar", like so:

"variables": {

        "myvar": "default_value"

}

Or, I can tell packer to read an env named MYVAR and assign it to the variable "myvar", like so:

"variables": {

        "myvar": "{{ env `MYVAR` }}"

}

However, with this method there is no default value.

For either method, I can also use "-var" on the command line to assign a value to the variable. 

What I'm looking to do is use the {{ env }} function, but _also_ assign a default value if the ENV is empty. I cannot find a way to do that within packer itself.

-Loren

[Alvaro Miranda Aguilera]

Hello,

Not possible as today.

2 Ways of doing it.

You could have a json file with vars.

myenv.json or mykey.json and use it at run time.

other way would be

in a variable block:

"myvar": "mydefault",

"myvarenv": "ENV[myvar]"

you pass both to the shell script and inside the shell you may check.

if [ "${myvarenv}" ]; then

  localvar="${myvarenv}"

elif [ "${myvar}" ]; then

  localvar="${myvar}"

fi

Unfortunately, i don't see other way as today.

Alvaro.

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[Loren Gordon]

Ok, thanks, I filed a feature request.

https://github.com/mitchellh/packer/issues/3457

-Loren