https://www.rfc-editor.org/rfc/rfc2616#section-5```text
Request = Request-Line ; Section 5.1
*(( general-header ; Section 4.5
| request-header ; Section 5.3
| entity-header ) CRLF) ; Section 7.1
CRLF
[ message-body ]
```
1. HTTP 是 CRLF 换行, 不是用不用 windows 的问题.
2. 在 Archlinux curl 7.88.1 下, HEAD
https://api.github.com/users/octocat, 返回为 http/2, header 为小写
```text
HTTP/2 404
server:
GitHub.comdate: Tue, 28 Feb 2023 01:45:47 GMT
content-type: application/json; charset=utf-8
content-length: 84
x-github-media-type: github.v3; format=json
x-github-api-version-selected: 2022-11-28
x-ratelimit-limit: 60
x-ratelimit-remaining: 52
x-ratelimit-reset: 1677550667
x-ratelimit-used: 8
x-ratelimit-resource: core
...省略
```
3. awk 设置 IGNORECASE=1 大小写不敏感, 如:
```bash
echo "${githubGetRateInfo}"|awk 'BEGIN{IGNORECASE=1}/^X-RateLimit-Limit:/{print $2}'|tr -d '\r'
```