Parse yaml file with varying number of key:values - bash

Question

Long story short, I will be parsing yaml files in a directory with bash using yq. My yaml files could look like this:
CLIENT_FIRST_NAME: bob
CLIENT_LAST_NAME: smith
Or
CLIENT_FIRST_NAME: bob
CLIENT_LAST_NAME: smith
CLIENT_MIDDLE_NAME: michael
So I am looping through each file with a do loop and setting the variables to values
For example:
for f in $FILES
do
FIRSTNAME=$(yq r $f CLIENT_FIRST_NAME)
LASTNAME=$(yq r $f CLIENT_LAST_NAME)
add client --firstname=${FIRSTNAME} --lastname=${LASTNAME}
done
But sometimes I will have that middle name and I would need to include that:
add client --firstname=${FIRSTNAME} --lastname=${LASTNAME} --middlename=${MIDDLENAME}
The order doesn't matter, I just need to be able to account for additional fields that may show up in the yaml that need to be added to the 'add client' command. EVERY line in the yaml will be added to the command. Every key added will be a viable parameter for the 'add client' command. I don't have to worry about whether or not a key in the yaml is a valid parameter. They WILL be.
Curious on the best approach to the unknown here. Thanks!

Answer 1

I'm assuming yq returns nothing if it doesn't find a key.
I might make the entire flag based on whether yq returns something, like
for f in "${FILES[#]}"
do
FIRSTNAME=$(yq r "$f" CLIENT_FIRST_NAME)
MIDDLENAME=$(yq r "$f" CLIENT_MIDDLE_NAME)
LASTNAME=$(yq r "$f" CLIENT_LAST_NAME)
[[ -n $MIDDLENAME ]] && MIDDLENAME="--middlename=${MIDDLENAME}"
add client --firstname="${FIRSTNAME}" --lastname="${LASTNAME}" "${MIDDLENAME}"
done

Answer 2

This code would be far more efficient if you only ran yq once per input file, not once per data item per input file. Consider:
for f in *.yml; do
{ read -r firstname; read -r middlename; read -r lastname; } < <(
yq -r '(.CLIENT_FIRST_NAME, .CLIENT_MIDDLE_NAME // "", .CLIENT_LAST_NAME)' "$f"
)
add client \
--firstname="$firstname" \
${middlename:+--middlename="$middlename"} \
--lastname="$lastname"
done
Some notes to use in reading this:
Each read command in bash reads one line, when -d is not used to modify this.
The above yq command outputs one line per data item.
Using // "" causes the empty string, instead of null, to be used when no CLIENT_MIDDLE_NAME is found.
${foo:+...words here...} expands to ...words here... if-and-only-if foo is set to a non-empty value.