How to include environment variable in bash line CURL?



Trying to get Transmission to notify when download complete.

This works:

curl -u <my-api-token>: \
  -X POST \
  --header 'Content-Type: application/json' \
  --data-binary '{"type": "note", "title": "$TR_TORRENT_NAME", \
  "body": "$TR_TORRENT_NAME completed."}'

... except it pushes $TR_TORRENT_NAME and not the actual contents of that variable.

Do I need to escape some quote or something?


Posted 2014-11-04T02:44:10.393

Reputation: 1 716



Inside single-quotes, the shell expands nothing. Place them inside double-quotes instead:

curl -u <my-api-token>: \
  -X POST \
  --header 'Content-Type: application/json' \
  --data-binary '{"type": "note", "title": "'"$TR_TORRENT_NAME"'", \
  "body": "'"$TR_TORRENT_NAME completed"'."}'

Let's examine how this works by looking at:

$ echo '{"type": "note", "title": "'"$TR_TORRENT_NAME"'", "body": "'"$TR_TORRENT_NAME completed"'."}'
{"type": "note", "title": "MyTorrent", "body": "MyTorrent completed."}

When the shell variable appears, it is always inside double-quotes. Consequently, it is properly expanded.

Quoting like this is a bit subtle. We have single-quoted strings that contain double-quotes as characters and are next to double-quoted strings. To understand this better, let's take this fragment as a an example:


Taking each character in turn:

  1. " is a literal double-quote character that is inside of a single-quoted string. (For brevity, the beginning of this string is not shown in this fragment.)

  2. ' closes a single-quoted string.

  3. " opens a double-quoted string.

  4. $TR_TORRENT_NAME is a shell variable that is expanded inside double-quotes.

  5. " closes the double-quoted string.

  6. ' opens a new single-quoted string.

  7. " places a double-quote character inside the single-quoted string.


Posted 2014-11-04T02:44:10.393

Reputation: 13 893

Do you need steps 3 and 5? – davidfrancis – 2018-01-18T11:39:28.500

@davidfrancis If one omits steps 3 and 5, then step 4 is subject to word splitting and pathname expansion and either one could cause all manor of trouble. Unless one explicitly wants word splitting and pathname expansion, a shell variable should always be inside double-quotes. – John1024 – 2018-01-18T20:49:11.160

Thanks for that, can you give a quick example please? It worked in my own example, which is why I asked, but there were no spaces or anything else complex in there – davidfrancis – 2018-01-19T09:10:18.937

@davidfrancis Try TR_TORRENT_NAME="A * B" and see what happens. – John1024 – 2018-01-20T08:17:14.407


To include an environment variable in a bash line curl without quotes around the variable content, this worked for me:


Or using the scenario that was first described without quotes around the body field:

curl -u <my-api-token>: \
  -X POST \
  --header 'Content-Type: application/json' \
  --data-binary '{"type": "note", "title": "'"$TR_TORRENT_NAME"'", \
  "body": '"$TR_TORRENT_NAME completed"'.}'

Brad Natelborg

Posted 2014-11-04T02:44:10.393

Reputation: 21