cURL operation performs differently when used in batch script - bash

Question

I'm a bit new to batch scripting, so I apologize if this is glaringly obvious, but I couldn't find any similar information.
I'm trying to perform the following cURL call:
curl -H "Content-Type:application/json" -d '{"lt":"f","sort":"n","max":"1500","offset":"1500"}' [API_KEY]#api.nal.usda.gov/ndb/list
When I run that line in a command line (or Cygwin) it does exactly what I want it to.
However, when I try to call it from a bat file, it seems my parameters are getting messed up somehow.
FOR /L %%A IN (0, 1500, 77500) DO (
curl -H "Content-Type:application/json" -d '{"lt":"f","sort":"n","max":"1500","offset":"%%A"}' [API_KEY]#api.nal.usda.gov/ndb/list > %%A.txt
)
I'm getting output into the correct .txt file, but it doesn't seem like the %%A in offset is getting replaced. I'm getting a "bad parameter" exception from the API. From the output on the command line, it looks accurate.
I'm open to using bash scripting instead if it would make more sense, but I was having the same issue using bash.
(Note: I replaced my API key with a placeholder in the example.. that's not the problem)

Answer 1

In bash at least, the problem is that variable expansion does not occur inside single quotes; you need to use double quotes and escape the nested double quotes:
for a in 0 1500 77500; do
curl -H "Content-Type:application/json" -d "{\"lt\":\"f\",\"sort\":\"n\",\"max\":\"1500\",\"offset\":\"$a\"}" [API_KEY]#api.nal.usda.gov/ndb/list > "$a".txt
)
I suspect you need to do the equivalent in a batch file.
You can concatenate adjacent single- and double-quoted strings to minimized the number of escaped quotes:
... -d '{"lt": "f", "sort": "n", "max": "1500", "offset": "'"$a"'"}' ...
but you may want to consider one of two other options. First, read the data from a here document instead of using a hard-coded string:
curl -H "..." -d#- [API_KEY]#api.nal.usda.gov/ndb/list > "$a".txt <<EOF
{"lt": "f", "sort": "n", "max": "1500", "offset": "$a"}
EOF
or use something like jq to generate the JSON for your:
curl -H "..." \
-d "$(jq --arg a "$a" '{lt: "f", sort: "n", max: "1500", offset: $a}') \
[API_KEY]#api.nal.usda.gov/ndb/list > "$a".txt
The jq solution would be preferable in general, since you don't have to worry about pre-escaping any variable values.