What’s the exit code for “curl -I” when not HTTP 200

You are including invalid HTTP headers in your request:

$header[ ] = "Accept: text/xml,application/xml,application/xhtml+xml,";
$header[ ] = "text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5";

On the first line, the list ends with a , – that is, an empty content type – which is the cause of 406 Not acceptable errors. The second line is not even a HTTP header.

If you were looking at Firefox HTTP conversations with a packet sniffer, you probably saw something like this:

Accept: text/xml,application/xml,application/xhtml+xml,
    text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5

Since the second line starts with whitespace, they are treated as a single header by the server. They must also be passed as one header to curl:

$header[] = "Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5";

You can use http://echo.opera.com to compare the requests being sent.

There is no need to use a temporary file. The following bash script snippet send a single request and prints the exit code of curl and the HTTP status code, or the HTTP status code and response, as appropriate.

# get output, append HTTP status code in separate line, discard error message
OUT=$( curl -qSfsw '\n%{http_code}' http://superuser.com ) 2>/dev/null

# get exit code
RET=$?

if [[ $RET -ne 0 ]] ; then
    # if error exit code, print exit code
    echo "Error $RET"

    # print HTTP error
    echo "HTTP Error: $(echo "$OUT" | tail -n1 )"
else
    # otherwise print last line of output, i.e. HTTP status code
    echo "Success, HTTP status is:"
    echo "$OUT" | tail -n1

    # and print all but the last line, i.e. the regular response
    echo "Response is:"
    echo "$OUT" | head -n-1
fi

head -n-1 (print all but the last line) requires GNU, doesn't work on BSD/OS X.