Is it a best practice to wrap paths in quotation marks?

Question

Consider the following code:

for domain; do
    cat << EOF > "/etc/nginx/sites-available/${domain}.conf"
        My \domain is ${domain}.
    EOF
done

Note that the path /etc/nginx/sites-available/${domain}.conf is wrapped with quotation marks. Is it a best practice or done because of variable substitution? If it's variable substitution, wouldn't it be better or more common to wrap the heredoc name (EOF) instead?

Answer 1

Quoting expressions which contain variables is a best-practice (as opposed to merely being a convention) in part because of variable expansion:

• When is double-quoting necessary?

If the variable expands to a string which contains white-space, for example, then your code would end up writing to to wrong file. Quoting the heredoc keyword does affect variable expansion, but not in the same way that quoting affects strings:

• Using variables inside a bash heredoc

Specifically, quoting the heredoc keyword prevents variable expansion.

And in any event, the path in question is not part of the heredoc body (which starts on the line after the first delimiter) and would therefore be unaffected - it has to be quoted independently.

Also note that (although this is unrelated to your question) the heredoc in your code snippet is invalid since the closing delimiter is indented. Consider the following excerpt from the Advanced Bash-Scripting Guide:

The closing limit string, on the final line of a here document, must start in the first character position. There can be no leading whitespace. Trailing whitespace after the limit string likewise causes unexpected behavior. The whitespace prevents the limit string from being recognized.

The exception to this is the <<- style heredocs, which ignore tab-indentation and also allow for the closing delimiter to be tab-indented. This is described in the following passage taken from the Wooledge Bash Wiki:

If you use <<-END instead of <<END as your Heredoc operator, Bash removes any tab characters in the beginning of each line of your Heredoc content before sending it to the command. That way you can still use tabs (but not spaces) to indent your Heredoc content with the rest of your code. Those tabs will not be sent to the command that receives your Heredoc. You can also use tabs to indent your sentinel string.