Cannot expand and substitute the contents of a variable in Bash - json

Question

I am using Gitbash, GNU bash, version 4.3.46(2)-release (x86_64-pc-msys).
I am running a bash script that looks like this
CODE CHUNK 1
curl -i -X POST \
-H "Content-Type:application/json" \
-H "x-customheader:customstuff" \
-d \
'{
Gigantic json payload contents in here
}' \
'http://localhost:5000/api/123'
This works fine. Basically it posts a giant payload to an endpoint and all is well. The problem is when I attempt to substitute the url for a value from a variable, I get a curl error,
curl: (1) Protocol "'http" not supported or disabled in libcurl
CODE CHUNK 2
stuff=\'http://localhost:5000/api/123\'
curl -i -X POST \
-H "Content-Type:application/json" \
-H "x-customheader:customstuff" \
-d \
'{
Gigantic json payload contents in here
}' \
$stuff
If I echo $stuff immediately after the stuff=\'http://localhost:5000/api/123\', I get 'http://localhost:5000/api/123'. This is the same value as I had hard-coded in code chunk 1, single ticks and all. There is something hiding behind the scenes in how that url is being evaluated after the variable has been expanded. I need to get the same behavior as a hard coded url.

Answer 1

Look closely at this error message:
curl: (1) Protocol "'http" not supported or disabled in libcurl
Notice the single-quote in front of http.
The curl command surely knows the http protocol, but not the 'http protocol!
The way you wrote it, the single-quotes are part of the value of stuff:
stuff=\'http://localhost:5000/api/123\'
Remove those, write like this:
stuff='http://localhost:5000/api/123'
If you have variables inside your real string,
and you want them expanded, then use double-quotes instead of single-quotes:
stuff="http://localhost:5000/api/123"
Equally important,
when you use $stuff as a parameter of curl,
you must double-quote it.
If you just write curl $stuff,
then the shell may interpret some characters in $stuff before passing to curl.
To protect from that,
you must write curl "$stuff".
The complete command:
curl -i -X POST \
-H "Content-Type:application/json" \
-H "x-customheader:customstuff" \
-d \
'{
Gigantic json payload contents in here
}' \
"$stuff"
Finally, make sure that after each \ at the end of lines,
there's nothing after the \ on each line,
the \ must be at the very end.

Answer 2

Why do you define stuff with the ' ' ?
Try it like that:
stuff="http://localhost:5000/api/123"
curl -i -X POST \
-H "Content-Type:application/json" \
-H "x-customheader:customstuff" \
-d \
'{
Gigantic json payload contents in here
}' \
"$stuff"
Also, don't put variables in single quotes, because bash is not available to understand them.
stuff="http://localhost:5000/api/123"
echo "$stuff"
>> http://localhost:5000/api/123
echo '$stuff'
>> $stuff