How can I set the request header for curl?

Just use the -H option several times:

curl -H "Accept-Charset: utf-8" -H "Content-Type: application/x-www-form-urlencoded" http://www.some-domain.example

Add additional -H or --header to your curl command:

//Simple
$ curl -v -H 'header1:val' -H 'header2:val' URL

//Explanatory
$ curl -v -H 'Connection: keep-alive' -H 'Content-Type: application/json'  https://www.example.com

For standard HTTP header fields such as User-Agent, Cookie, Host, another way to set them is designated curl command options:

• -A / --user-agent: "User-Agent"
• -b / --cookie: "Cookie"
• -e / --referer: "Referer"
• -H / --header: "Header"

These commands are equivalent. Both change "User-Agent" in the HTTP header.

$ curl -v -H "Content-Type: application/json" -H "User-Agent: UserAgentString" https://www.example.com
$ curl -v -H "Content-Type: application/json" -A "UserAgentString" https://www.example.com

Sometimes changing the header is not enough, some sites check the referer as well:

curl -v \
     -H 'Host: restapi.some-site.com' \
     -H 'Connection: keep-alive' \
     -H 'Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8' \
     -H 'Accept-Language: en-GB,en-US;q=0.8,en;q=0.6' \
     -e localhost \
     -A 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/29.0.1547.65 Safari/537.36' \
     'http://restapi.some-site.com/getsomething?argument=value&argument2=value'

In this example the referer (-e or --referer in curl) is 'localhost'.

Set Header -H "Content-Type: application/json" using GET Request

Example -

curl -H "Content-Type: application/json" -X GET https://jsonplaceholder.typicode.com/posts/1

If u want to Add multiple header

curl -H "Connection: keep-alive" -H "Content-Type: application/json -X GET https://jsonplaceholder.typicode.com/posts/1