How to echo variables inside an ANSI quoted string - bash

Question

I need to execute a curl command like this:
#!/bin/bash
shopid=9932781
itemid=231873991
curl -sSb /tmp/cookies 'https://website.com' -H 'cookie: csrftoken=mytoken' -H 'x-csrftoken: mytoken' -H 'content-type: multipart/form-data; boundary=----WebKitFormBoundary' -H 'referer: https://website.com' \
--data-binary $'------WebKitFormBoundary\r\nContent-Disposition: form-data; name="shopid"\r\n\r\n${shopid}\r\n------WebKitFormBoundary\r\nContent-Disposition: form-data; name="itemid"\r\n\r\n${itemid}\r\n------WebKitFormBoundary\r\nContent-Disposition: form-data; name="quantity"\r\n\r\n1\r\n------WebKitFormBoundary\r\nContent-Disposition: form-data; name="donot_add_quantity"\r\n\r\nfalse\r\n------WebKitFormBoundary\r\nContent-Disposition: form-data; name="update_checkout_only"\r\n\r\nfalse\r\n------WebKitFormBoundary\r\nContent-Disposition: form-data; name="source"\r\n\r\n\r\n------WebKitFormBoundary\r\nContent-Disposition: form-data; name="checkout"\r\n\r\ntrue\r\n------WebKitFormBoundary--\r\n'
The $'' quotes are necessary or else (ie. in the double-quoted case) \r\n won't work -- but with this form, $shopid and $item aren't replaced with their values.
How can I get both behaviors?

Answer 1

You need to make that code maintainable
binary_data=$( cat <<END_DATA | sed 's/$/\r/'
------WebKitFormBoundary
Content-Disposition: form-data; name="shopid"
${shopid}
------WebKitFormBoundary
Content-Disposition: form-data; name="itemid"
${itemid}
------WebKitFormBoundary
Content-Disposition: form-data; name="quantity"
1
------WebKitFormBoundary
Content-Disposition: form-data; name="donot_add_quantity"
false
------WebKitFormBoundary
Content-Disposition: form-data; name="update_checkout_only"
false
------WebKitFormBoundary
Content-Disposition: form-data; name="source"
------WebKitFormBoundary
Content-Disposition: form-data; name="checkout"
true
------WebKitFormBoundary--
END_DATA
)
curl_opts=(
-sSb /tmp/cookies
-H 'cookie: csrftoken=mytoken'
-H 'x-csrftoken: mytoken'
-H 'content-type: multipart/form-data; boundary=----WebKitFormBoundary'
-H 'referer: https://website.com'
--data-binary "$binary_data"
)
curl "${curl_opts[#]}" 'https://website.com'

Answer 2

You can use multiple quoting styles within a single string. Thus:
$'Constant\r\n\n\r\n'"$bar"
...has the \r\ns parsed with $'...' rules, but the $bar expanded with double-quoting rules (such that the expansion also takes place).

Answer 3

The variables are not expanded in 'single quotes'.
It's important to learn how quoting works :
"Double quote" every literal that contains spaces/metacharacters and every expansion: "$var", "$(command "$var")", "${array[#]}", "a & b". Use 'single quotes' for code or literal $'s: 'Costs $5 US', ssh host 'echo "$HOSTNAME"'. See
http://mywiki.wooledge.org/Quotes
http://mywiki.wooledge.org/Arguments
http://wiki.bash-hackers.org/syntax/words
So, try this :
data="------WebKitFormBoundary
Content-Disposition: form-data; name='shopid'
${shopid}
------WebKitFormBoundary
Content-Disposition: form-data; name='itemid'
${itemid}
------WebKitFormBoundary
Content-Disposition: form-data; name='quantity'
1
------WebKitFormBoundary
Content-Disposition: form-data; name='donot_add_quantity'
false
------WebKitFormBoundary
Content-Disposition: form-data; name='update_checkout_only'
false
------WebKitFormBoundary
Content-Disposition: form-data; name='source'
------WebKitFormBoundary
Content-Disposition: form-data; name='checkout'
true
------WebKitFormBoundary--"
data="$(sed 's/$/\r/' <<< "$data")"
curl -sSb /tmp/cookies \
-H 'cookie: csrftoken=mytoken' \
-H 'x-csrftoken: mytoken' \
-H 'content-type: multipart/form-data; boundary=----WebKitFormBoundary' \
-H 'referer: https://website.com' \
--data-binary "$data" \
'https://website.com'