Scripted concatenation of strings in curl command payload - bash

Question

I use curl to test an user account creation API as follows:
curl -s -X POST "https://$APISERVER/users" \
-H 'Content-Type: application/json' \
-d '{ \
"username": "'$NEWUSERNAME'", \
"firstName": "'$NEWUSERFIRSTNAME'", \
"lastName": "'$NEWUSERLASTNAME'", \
"displayName": "'$NEWUSERDISPLAYNAME'", \
"password": "'$NEWUSERPASSWORD'" \
}'
and the variables are supplied via command line arguments:
APISERVER=http://localhost:8080
NEWUSERNAME=$1
NEWUSERPASSWORD=$2
NEWUSERFIRSTNAME=$3
NEWUSERLASTNAME=$4
# Calculated variable
NEWUSERDISPLAYNAME="${NEWUSERFIRSTNAME} ${NEWUSERLASTNAME}"
An example invocation of the script is as follows: ./test-new-user.sh jdoe Hello123 John Doe, resulting in the following variable values:
NEWUSERNAME=jdoe
NEWUSERPASSWORD=Hello123
NEWUSERFIRSTNAME=John
NEWUSERLASTNAME=Doe
(I intended NEWUSERDISPLAYNAME to be set to "John Doe")
But I get back an exception from the server, because the payload in the curl command appears to be cut-off, incomplete or malformed.
JSON parse error: Unexpected end-of-input in VALUE_STRING\n at [Source:
java.io.PushbackInputStream#2eda6052; line: 1, column: 293]; nested
exception is com.fasterxml.jackson.databind.JsonMappingException:
Unexpected end-of-input in VALUE_STRING\n at [Source:
java.io.PushbackInputStream#2eda6052; line: 1, column: 293]\n at
[Source: java.io.PushbackInputStream#2eda6052; line: 1, column: 142]
(through reference chain:
com.mycompany.api.pojos.NewUser[\"displayName\"])"
If I hard code value for displayName in the above curl command (as below), the user creation request goes through and works perfectly.
"displayName": "John Doe", \
I suspect it has to do with the space in displayName and how I insert the value for displayName using "'$NEWUSERDISPLAYNAME'". Is there a safe way to perform variable substitution in the curl command's POST request payload?

Answer 1

You need to quote shell variables:
curl -s -X POST "https://$APISERVER/users" \
-H 'Content-Type: application/json' \
-d '{ \
"username": "'"$NEWUSERNAME"'", \
"firstName": "'"$NEWUSERFIRSTNAME"'", \
"lastName": "'"$NEWUSERLASTNAME"'", \
"displayName": "'"$NEWUSERDISPLAYNAME"'", \
"password": "'"$NEWUSERPASSWORD"'" \
}'
In order to avoid excessive quoting, try this printf:
printf -v json -- '{ "username": "%s", "firstName": "%s", "lastName": "%s", "displayName": "%s", "password": "%s" }' \
"$NEWUSERNAME" "$NEWUSERFIRSTNAME" "$NEWUSERLASTNAME" "$NEWUSERDISPLAYNAME" "$NEWUSERPASSWORD"
curl -s -X POST "https://$APISERVER/users" \
-H 'Content-Type: application/json' \
-d "$json"

Answer 2

just use
$(echo $varname)
works for me