If you want to capture the HTTP status code in a variable, but still redirect the content to STDOUT, you must create two STDOUTs. You can do so with process substitution >() and command substitution $().

First, create a file descriptor 3 for your current process' STDOUT with exec 3>&1.

Then, use curl's -o option to redirect the response content to a temporary fifo using command substitution, and then within that command substitution, redirect output back to your current process STDOUT file descriptor 3 with -o >(cat >&3).

Putting it all together in bash 3.2.57(1)-release (standard for macOS):

#creates a new file descriptor 3 that redirects to 1 (STDOUT)
exec 3>&1 
# Run curl in a separate command, capturing output of -w "%{http_code}" into HTTP_STATUS
# and sending the content to this command's STDOUT with -o >(cat >&3)
HTTP_STATUS=$(curl -w "%{http_code}" -o >(cat >&3) 'http://example.com')

Note that this doesn't work in /bin/sh as SamK noted in the comments below.

If you want to capture the HTTP status code in a variable, but still redirect the content to STDOUT, you must create two STDOUTs. You can do so with process substitution >() and command substitution $().

First, create a file descriptor 3 for your current process' STDOUT with exec 3>&1.

Then, use curl's -o option to redirect the response content to a temporary fifo using command substitution, and then within that command substitution, redirect output back to your current process STDOUT file descriptor 3 with -o >(cat >&3).

Putting it all together in bash 3.2.57(1)-release (standard for macOS):

# creates a new file descriptor 3 that redirects to 1 (STDOUT)
exec 3>&1 
# Run curl in a separate command, capturing output of -w "%{http_code}" into HTTP_STATUS
# and sending the content to this command's STDOUT with -o >(cat >&3)
HTTP_STATUS=$(curl -w "%{http_code}" -o >(cat >&3) 'http://example.com')

Note that this doesn't work in /bin/sh as SamK noted in the comments below.

If you want to capture the HTTP status code in a variable, but still redirect the content to STDOUT, you must create two STDOUTs. You can do so with process substitution >() and command substitution $().

First, create a file descriptor 3 for your current process' STDOUT with exec 3>&1.

Then, use curl's -o option to redirect the response content to a temporary fifo using command substitution, and then within that command substitution, redirect output back to your current process STDOUT file descriptor 3 with -o >(cat >&3).

Putting it all together:

#creates a new file descriptor 3 that redirects to 1 (STDOUT)
exec 3>&1 
# Run curl in a separate command, capturing output of -w "%{http_code}" into HTTP_STATUS
# and sending the content to this command's STDOUT with -o >(cat >&3)
HTTP_STATUS=$(curl -w "%{http_code}" -o >(cat >&3) 'http://example.com')

If you want to capture the HTTP status code in a variable, but still redirect the content to STDOUT, you must create two STDOUTs. You can do so with process substitution >() and command substitution $().

First, create a file descriptor 3 for your current process' STDOUT with exec 3>&1.

Then, use curl's -o option to redirect the response content to a temporary fifo using command substitution, and then within that command substitution, redirect output back to your current process STDOUT file descriptor 3 with -o >(cat >&3).

Putting it all together in bash 3.2.57(1)-release (standard for macOS):

#creates a new file descriptor 3 that redirects to 1 (STDOUT)
exec 3>&1 
# Run curl in a separate command, capturing output of -w "%{http_code}" into HTTP_STATUS
# and sending the content to this command's STDOUT with -o >(cat >&3)
HTTP_STATUS=$(curl -w "%{http_code}" -o >(cat >&3) 'http://example.com')

Note that this doesn't work in /bin/sh as SamK noted in the comments below.