host -t TXT gmx.de|grep -i spf
    dig heise.de TXT|grep -i spf
    dig gmx.de TXT|grep -i spf
    dig gmx.net TXT|grep -i spf
    nslookup -q=TXT gmx.net|grep -i spf

    tcpdump -n port 10011 -vv

    nc -vz -u 192.168.100.100 10011

    nc -luk 192.168.100.100 20000

    nc -uv  192.168.100.100 20000
    hello host!<ENTER>

    ​~~~mermaid
    graph TB
        A --> B
        B --> C
    ​~~~

    ​~~~mermaid
    erDiagram
            CUSTOMER }|..|{ DELIVERY-ADDRESS : has
            CUSTOMER ||--o{ ORDER : places
            CUSTOMER ||--o{ INVOICE : "liable for"
            DELIVERY-ADDRESS ||--o{ ORDER : receives
            INVOICE ||--|{ ORDER : covers
            ORDER ||--|{ ORDER-ITEM : includes
            PRODUCT-CATEGORY ||--|{ PRODUCT : contains
            PRODUCT ||--o{ ORDER-ITEM : "ordered in"
    ​~~~

    ~~~mermaid
    stateDiagram-v2
        [*] --> Still
        Still --> [*]
        Still --> Moving
        Moving --> Still
        Moving --> Crash
        Crash --> [*]
    ​~~~

    ~~~mermaid
    gitGraph
    commit
    commit
    branch two
    commit
    checkout main
    commit
    branch three
    checkout three
    commit
    commit
    checkout main
    commit
    commit
    branch one
    checkout one
    commit
    checkout two
    commit
    checkout main
    merge two
    checkout one
    merge two
    merge three
    commit
    commit
    checkout main
    merge one
    ​~~~

    ~~~mermaid
    sequenceDiagram
            title: FancySequenceDiagramaccDescription Test a description
            participant Alice
            participant Bob
            participant John as John<br />Second Line
            rect rgb(20, 20, 100)
            rect rgb(0, 5, 200)
            Alice ->> Bob: Hello Bob, how are you?
            Bob-->>John: How about you John?
            end
            Bob--x Alice: I am good thanks!
            Bob-x John: I am good thanks!
            Note right of John: John thinks a long<br />long time, so long<br />that the text does<br />not fit on a row.
            Bob-->Alice: Checking with John...
            Note over John:wrap: John looks like he's still thinking, so Bob prods him a bit.
            Bob-x John: Hey John - we're still waiting to know<br />how you're doing
            Note over John:nowrap: John's trying hard not to break his train of thought.
            Bob-x John:wrap: John! Are you still debating about how you're doing? How long does it take??
            Note over John: After a few more moments, John<br />finally snaps out of it.
            end
            alt either this
            Alice->>+John: Yes
            John-->>-Alice: OK
            else or this
            Alice->>John: No
            else or this will happen
            Alice->John: Maybe
            end
            par this happens in parallel
            Alice -->> Bob: Parallel message 1
            and
            Alice -->> John: Parallel message 2
            end
    ​~~~

    ~~~mermaid
        sequenceDiagram
            Alice->>+John: Hello John, how are you?
            Alice->>+John: John, can you hear me?
            John-->>-Alice: Hi Alice, I can hear you!
            John-->>-Alice: I feel great!
    ​~~~

    ~~~mermaid
    pie
    "Dogs" : 42.96
    "Cats" : 50.05
    "Rats" : 10.01
    ​~~~

    echo | openssl s_client -servername $DOMAIN -connect HOST:PORT 2>/dev/null | openssl x509 -noout -enddate

    openssl x509 -enddate -noout -in file.pem

    cat file.pem | openssl x509 -noout -enddate

    openssl pkcs12 -in mycert.p12 -nodes | openssl x509 -noout -enddate