Tab multiline variable to heredoc

I’m trying to add a multiline variable into a heredoc that will be put into a markdown file.

My script looks like this:

markdown=$(cat <<-EOF
<details>
    <summary>TEST</summary>

    ${output}
</details>
EOF
)

echo "$markdown" >> test.md

Where output is a multi line string:

this
is a
multiline
string

When I run the script the output looks like:

<details>
    <summary>TEST</summary>

    this
is a
multiline
string
</details>

How can I get it so that not just the first line of the output variable is tabbed correctly? I’ve tried running the variable through sed and adding tabs, but that doesn’t work

>Solution :

You have to indent it. Yourself. For example, add 4 spaces in front of every line by using sed:

cat <<-EOF
<details>
    <summary>TEST</summary>

$(sed 's/^/    /' <<<"$output")
</details>
EOF

You could replace newlines with a newline and 4 spaces:

cat <<-EOF
<details>
    <summary>TEST</summary>

    ${output//$'\n'/$'\n'    }
</details>
EOF