bash function with third arg is an array - bash

Question

I'm trying to write a bash function that does the following:
If there is no 3rd argument, run a command.
If there is a third argument, take every argument from the third one and run a command.
The problem I have is the last bit of the command --capabilities CAPABILITY_IAM in the else statement that I don't want to pass in all the time if I have multiple parameters.
An error occurred (InsufficientCapabilitiesException) when calling the CreateStack operation: Requires capabilities : [CAPABILITY_NAMED_IAM]
// that means I need to pass in --capabilities CAPABILITY_IAM
Is there a way to tell bash that: hey, take all the args from the 3rd one, then add the --capabilities CAPABILITY_IAM after? Like in JavaScript I can do this:
function allTogetherNow(a, b, ...c) {
console.log(`${a}, ${b}, ${c}. Can I have a little more?`);
}
allTogetherNow('one', 'two', 'three', 'four')
Here's my function:
cloudformation_create() {
if [ -z "$3" ]; then
aws cloudformation create-stack --stack-name "$1" --template-body file://"$2" --capabilities CAPABILITY_IAM
else
aws cloudformation create-stack --stack-name "$1" --template-body file://"$2" --parameters "${#:3}" --capabilities CAPABILITY_IAM
fi
}
And the 3rd and so on parameters look like this if I don't use a bash function:
aws cloudformation create-stack --stack-name MY_STACK_NAME --template-body file://MY_FILE_NAME --parameters ParameterKey=KeyPairName,ParameterValue=TestKey ParameterKey=SubnetIDs,ParameterValue=SubnetID1 --capabilities CAPABILITY_IAM
Update 22 May 2019:
Following Dennis Williamson's answer below. I've tried:
Passing the parameters in the AWS way:
cloudformation_create STACK_NAME FILE_NAME ParameterKey=KeyPairName,ParameterValue=TestKey ParameterKey=SubnetIDs,ParameterValue=SubnetID1
Got error:
An error occurred (ValidationError) when calling the CreateStack operation: Parameters: [...] must have values
Pass in as a string:
cloudformation_create STACK_NAME FILE_NAME "ParameterKey=KeyPairName,ParameterValue=TestKey ParameterKey=SubnetIDs,ParameterValue=SubnetID1"
Got error:
An error occurred (ValidationError) when calling the CreateStack operation: ParameterValue for ... is required
Pass in without ParameterKey and ParameterValue:
cloudformation_create STACK_NAME FILE_NAME KeyPairName=TestKey SubnetIDs=SubnetID1
Got error:
Parameter validation failed:
Unknown parameter in Parameters[0]: "PARAM_NAME", must be one of: ParameterKey, ParameterValue, UsePreviousValue, ResolvedValue
// list of all the params with the above error
Pass in without ParameterKey and ParameterValue and as a string. Got error:
arameter validation failed:
Unknown parameter in Parameters[0]: "PARAM_NAME", must be one of: ParameterKey, ParameterValue, UsePreviousValue, ResolvedValue
I tried Alex Harvey's answer and got this:
An error occurred (ValidationError) when calling the CreateStack operation: Template format error: unsupported structure.

Answer 1

Based on LeBlue's answer and a quick read of the docs, it looks like you need to build the argument to --parameters from the arguments to the function:
cloudformation_create () {
local IFS=,
local parameters="${*:3}"
#if block not shown
aws cloud_formation ... --parameters "$parameters" ...
this presumes that your function is called like this:
cloudformation_create foo bar baz=123 qux=456
that is, with the key, value pairs already formed.
The snippet above works by setting IFS to a comma. Using $* inside quotes causes the elements contained in it to be joined using the first character of IFS. If you need to make use of the word splitting features in another part of your function, you may want to save the current value of IFS before changing it then restore it after the joining assignment.
As a result, the expansion of $parameters will be baz=123,qux=456

Answer 2

I am not sure that answers your question but maybe it will help you.
$# is the number of parameters.
$# will include all parameters and you can pass that.
#!/bin/bash
foo()
{
echo "params in foo: " $#
echo "p1: " $1
echo "p2: " $2
echo "p3: " $3
}
echo "number of paramters: " $#
foo $# 3 # pass params and add one to the end
Call:
./test.sh 1 2
Output:
number of paramters: 2
params in foo: 3
p1: 1
p2: 2
p3: 3

Answer 3

I suspect the parameter expansion is wrong, as --parameters probably needs to have one argument.
Either quote all arguments to cloudformation_create that need to end up as value for the --parameters flag:
cloudformation_create "the-stack" "the-filename" "all the parameters"
or rewrite the function to not expand into multiple arguments with "$*" (merge every arg into one)
cloudformation_create () {
...
else
aws cloudformation ... --parameters "${*:3}" --capabilities CAPABILITY_IAM
fi
}
This will preserve all values as one string/argument, both will translate to:
aws cloudformation ... --parameters "all other parameters" --capabilities CAPABILITY_IAM
as opposed to your version:
aws cloudformation ... --parameters "all" "other" "parameters" --capabilities CAPABILITY_IAM

Answer 4

First of all, thank you all for your help.
I've realised the issue (and my mistake):
AWS returned the error with Requires capabilities : [CAPABILITY_NAMED_IAM] and my function has [CAPABILITY_IAM].
Depends on the template with params related to creating IAM, [CAPABILITY_NAMED_IAM] or [CAPABILITY_IAM] is required. I found the answer here helpful.
So in my case, the bash function is good, for the template I was trying to create, I need to pass in --capabilities CAPABILITY_NAMED_IAM. I've tried it and it works.

Answer 5

I would write it this way:
cloudformation_create() {
local stack_name=$1
local template_body=$2
shift 2 ; local parameters="$#"
local command=(aws cloudformation create-stack
--stack-name "$stack_name"
--template-body "file://$template_body")
[ ! -z "$parameters" ] && \
command+=(--parameters "$parameters")
command+=(--capabilities CAPABILITY_IAM)
${command[#]}
}
Note:
calling shift 2 results in $3 being rotated to $1 such that you can just use $# as normal.