Using Environment Variables in cURL Command - Unix

Question

My question is very simple. I want to use environment variables in a cURL command sth similar to this:

curl -k -X POST -H 'Content-Type: application/json' -d '{"username":"$USERNAME","password":"$PASSWORD"}' 

When I run the command $USERNAME is passed to the command as a "$USERNAME" string not the value of the variable. Is there a way to escape this situation?

Thanks.

Answer 1

curl -k -X POST -H 'Content-Type: application/json' -d '{"username":"'$USERNAME'","password":"'$PASSWORD'"}'

Here the variable are placed outside of "'" quotes and will be expanded by shell (just like in echo $USERNAME). For example assuming that USRNAME=xxx and PASSWORD=yyy the argv[7] string passed to curl is {"username":"xxx","password":"yyy"}

And yes, this will not work when $USERNAME or $PASSWORD contain space characters.

Answer 2

Our: curl -k -X POST -H 'Content-Type: application/json' -d '{"username":"'"$USERNAME"'","password":"'"$PASSWORD"'"}'

Answer 3

Single quotes inhibit variable substitution, so use double quotes. The inner double quotes must then be escaped.

...  -d "{\"username\":\"$USERNAME\",\"password\":\"$PASSWORD\"}"

Answer 4

For less quoting, read from standard input instead.

curl -k -X POST -H 'Content-Type: application/json' -d @- <<EOF
{ "username": "$USERNAME", "password": "$PASSWORD"}
EOF

-d @foo reads from a file named foo. If you use - as the file name, it reads from standard input. Here, standard input is supplied from a here document, which is treated as a double-quoted string without actually enclosing it in double quotes.