Simple slack webhook client.
dotnet tool install -g SlackWebhookCli
$ slack-webhook -url https://hooks.slack.com/services/XXXXX/YYYYY/zzzzzzzzzzzzzzzzzz -text "Hello, Slack!"
$ cat hello.txt | slack-webhook -url https://hooks.slack.com/services/XXXXX/YYYYY/zzzzzzzzzzzzzzzzzz
$ slack-webhook -url https://hooks.slack.com/services/XXXXX/YYYYY/zzzzzzzzzzzzzzzzzz \
-text "Hello, Slack!" \
-channel "#dotnet" \
-userName "cssho"