Tab multiline variable to heredoc

Question

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

Answer 1

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

Answer 2

If you want leading tabs treated literally then don't tell the shell not to treat them literally, i.e. remove the - you had added before the first EOF:

cat <<EOF
    whatever
EOF

Not the problem you asked about but don't populate a variable from a here doc then echo it to a file, just redirect the cat output to a file:

cat <<EOF > file
    whatever
EOF

or if you want to store the text in a variable then don't use a here-doc:

markdown="<details>
    <summary>TEST</summary>

    $output
</details>"

printf '%s\n' "$markdown" > file