How to use a variable in a CURL request with bash? - bash

Question

Goal:
I'm using a bash CURL script to connect to the Cloudflare APIv4. The goal is to update an A-record. My script:
# Get current public IP
current_ip=curl --silent ipecho.net/plain; echo
# Update A record
curl -X PUT "https://api.cloudflare.com/client/v4/zones/ZONEIDHERE/dns_records/DNSRECORDHERE" \
-H "X-Auth-Email: EMAILHERE" \
-H "X-Auth-Key: AUTHKEYHERE" \
-H "Content-Type: application/json" \
--data '{"id":"ZONEIDHERE","type":"A","name":"example.com","content":"'"${current_ip}"'","zone_name":"example.com"}'
Problem:
The current_ip variable is not printed when I call it in my script. The output will be "content" : "" and not "content" : "1.2.3.4".
I used other stackoverflow posts and I'm trying to follow their examples but I think I'm still doing something wrong, just can't figure out what. :(

Answer 1

Using jq for this, as Charles Duffy's answer suggests, is a very good idea. However, if you can't or do not want to install jq here is what you can do with plain POSIX shell.
#!/bin/sh
set -e
current_ip="$(curl --silent --show-error --fail ipecho.net/plain)"
echo "IP: $current_ip"
# Update A record
curl -X PUT "https://api.cloudflare.com/client/v4/zones/ZONEIDHERE/dns_records/DNSRECORDHERE" \
-H "X-Auth-Email: EMAILHERE" \
-H "X-Auth-Key: AUTHKEYHERE" \
-H "Content-Type: application/json" \
--data #- <<END;
{
"id": "ZONEIDHERE",
"type": "A",
"name": "example.com",
"content": "$current_ip",
"zone_name": "example.com"
}
END

Answer 2

The reliable way to edit JSON from shell scripts is to use jq:
# set shell variables with your contents
email="yourEmail"
authKey="yourAuthKey"
zoneid="yourZoneId"
dnsrecord="yourDnsRecord"
# make sure we show errors; --silent without --show-error can mask problems.
current_ip=$(curl --fail -sS ipecho.net/plain) || exit
# optional: template w/ JSON content that won't change
json_template='{"type": "A", "name": "example.com"}'
# build JSON with content that *can* change with jq
json_data=$(jq --arg zoneid "$zoneid" \
--arg current_ip "$current_ip" \
'.id=$zoneid | .content=$current_ip' \
<<<"$json_template")
# ...and submit
curl -X PUT "https://api.cloudflare.com/client/v4/zones/$zoneid/dns_records/$dnsrecord" \
-H "X-Auth-Email: $email" \
-H "X-Auth-Key: $authKey" \
-H "Content-Type: application/json" \
--data "$json_data"