[SOLVED] Using Environment Variables in cURL Command - Unix

Issue

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.

Solution

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

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

---

Since this answer was written in 2015, it has become clear that this technique is insufficient to properly create JSON:

$ USERNAME=person1
$ PASSWORD="some \"gnarly 'password"
$ echo "{\"username\":\"$USERNAME\",\"password\":\"$PASSWORD\"}"
{"username":"person1","password":"some "gnarly 'password"}
$ echo "{\"username\":\"$USERNAME\",\"password\":\"$PASSWORD\"}" | jq .
parse error: Invalid numeric literal at line 1, column 47

The quoting problem are clear. The (shell) solutions are not

Current best practice: use a JSON-specific tool to create JSON:

• jq

  $ jq -n -c --arg username "$USERNAME" --arg password "$PASSWORD" '$ARGS.named'
  {"username":"person1","password":"some \"gnarly 'password"}
  

• jo

  $ jo "username=$USERNAME" "password=$PASSWORD"
  {"username":"person1","password":"some \"gnarly 'password"}
  

And with curl:

json=$( jq -n -c --arg username "$USERNAME" --arg password "$PASSWORD" '$ARGS.named' )
# or
json=$( jo "username=$USERNAME" "password=$PASSWORD" )

# then
curl ... -d "$json"

Answered By - glenn jackman

Answer Checked By - Katrina (WPSolving Volunteer)