base64: invalid input error when trying to decode contents of yaml file

Question

What specific syntax must be changed in the bash below to successfully decode the base64 encoded value which is throwing the error below?

THE ERROR:

The following 3 simple commands are typed into the terminal of a RHEL 8 vm running in Azure:

[user@myVM ~]$ myVar=$(az keyvault secret show --name "secretName" --vault-name "vaultName" --query "value")
[user@myVM ~]$ echo $myVar
"very.long.base64.encoded.string.representing.the.original.yaml"
[user@myVM ~]$ echo $myVar | base64 --decode
base64: invalid input

The second command prints what looks like valid base64 encoding of a long string, perhaps a few hundred characters or more encoded.

The error base64: invalid input seems to indicate that the base64 program is not able to accept the encoded input into its decode command.

THE SOURCE DATA:

The contents of the base64 encoded data above originated in a yaml file with perhaps 20 lines, which was passed through terraform's fileBase64() command as follows before the VM was created:

resource "azurerm_key_vault_secret" "secretName" {
  name         = "secretName"
  value        = filebase64(var.keySourceFile) 
  key_vault_id = azurerm_key_vault.vaultName.id
}

RESULTS OF TRYING USER SUGGESTIONS:

Per @roaima suggestion, we tried the following:

[user@myVM ~]$ az keyvault secret show --name "secretName" --vault-name "vaultName" --query "value"
"very.long.base64.encoded.string.representing.the.original.yaml=="
[user@myVM ~]$ myVar=$(az keyvault secret show --name "secretName" --vault-name "vaultName" --query "value")
[user@myVM ~]$ echo "$myVar" | base64 --decode >/dev/null 
base64: invalid input 

As you can see, we validated that a long encoded string is presented by the raw command before we put it into myVar . Note that it ends with == and is surrounded by double-quotes.

The raw data in the original source file that was sent into terraform looks something like:

secret1: value1
secret2: value2 
...
secretN: valueN

Then we tried the following but you can see nothing was returned:

[user@myVM ~]$ printf '%s\n' "$myVar" | base64 --decode --ignore-garbage >/dev/null
[user@myVM ~]$

Answer 1

Always double-quote your variables when you use them^*.

Repeatable example

myVar=$(perl -e 'print "hello, world. " x100, "\n"' | base64)
echo "$myVar"
echo $myVar | base64 --decode >/dev/null      # Fails
base64: invalid input
echo "$myVar" | base64 --decode >/dev/null    # Works

What's happening is that the quoted variable produces N lines of 76 characters, but the unquoted variable produces 1 line of 76 x N characters plus a space between each group of 76. This second output is not valid base64 format.

Reading comments and feedback, it seems that the source base64 data is still not completely compatible with the base64 command. In this instance it's necessary to skip unexpected characters:

printf '%s' "$myVar" | base64 --decode --ignore-garbage

Here I have also switched from using echo to printf (without a trailing newline) so that the output is better controlled.

---

^{* Except when you really know you have a necessary reason not to quote. These cases are few and far between. If in doubt, quote.}