1

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.
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10
  • That function looks good to me. How is it not working? Commented May 21, 2019 at 21:43
  • @DennisWilliamson it needs the --capabilities CAPABILITY_IAM at the end. For some reason, my bash function takes all the args but doesn't add the capability at the end. Commented May 21, 2019 at 22:56
  • 1
    What happens when you use your Bash function (just below "Here's my function:" above) which uses "${@:3}" (instead of the asterisk)? Commented May 22, 2019 at 14:37
  • 1
    We don't add "solved" to question titles on Stack Overflow. Please post your solution as an answer. You can even mark your own answer as accepted. Commented May 22, 2019 at 15:10
  • 1
    @Viet, fyi, the "unsupported structure" is because of a typo on my part ; I missed the "file://" bit. I've updated. Commented May 22, 2019 at 15:29

5 Answers 5

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3

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

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1 Comment

I'm sorry. This doesn't work. I'll update my question with what I got from your code.
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
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1 Comment

Thank you @Chris. Unfortunately, this is not what I'm looking for, I need something like this: foo $1 $2 $3 $4 (and so on) then does: do $1 and $2 and do $3 $4 $5 then do the last bit
1

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
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2 Comments

I think you may be close. The docs indicate that the argument to --parameters is a comma-delimited list of key=value pairs.
I think you're close. Like @DennisWilliamson wrote above, the --parameters is a list. I've updated my question above.
0

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.

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Comments

0

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.
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1 Comment

You can do shift 2. Putting commands, options and arguments in variables is discouraged.

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