---
name: "nngcat"
section: "1"
platform: "linux"
package: "nng-utils"
version: "1.10.1-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/nngcat"
---

# nngcat(1)

command line access to Scalability Protocols

## NAME

nngcat - command line access to Scalability Protocols

## SYNOPSIS

**nngcat** --help

**nngcat** --version

**nngcat** \[*OPTION*\]...

## DESCRIPTION

The *nngcat* utility provides command line access to the Scalability Protocols, making it possible to write shell scripts that interact with other peers in a Scalability Protocols topology, by both sending and receiving messages.

## OPTIONS

The possible values for *OPTION* are described below.

**Tip**\

The *nngcat* utility accepts shortened versions of these options, as long as the supplied option is unambiguous. For example `--comp` can be used in lieu of `--compat`, but `--re` may not be used for anything because it could mean any of `--req`, `--rep`, or `--respondent`.

When using the long form of an option (names prefixed with with `--`), if the option takes a value then the value may be supplied by appending the option with an equals sign and the value (e.g. `--subscribe=times`), by appending the option with a colon and the value (e.g. `--subscribe:tribune`) or by providing the data as the next program argument (e.g. `--subscribe herald`).

When using short form options (a single letter prefixed with a `-`), if the option takes a value it may either be immediately appended to the value (e.g. `-L5678`) or provided as the next program argument (e.g. `-L 5678`).

POSIX style option clustering of single letter options is not supported; each option must be presented as a separate argument to the program.

### Generic Options

- **-h, --help**

  Get usage help.

- **-V, --version**

  Print the version and exit.

- **-v, --verbose**

  Select verbose operation.

- **-q, --silent**

  Select silent operation.

- **--compat**

  Compatible mode. This cause *nngcat* to behave more like the legacy *nanocat* application. In this mode connections are made asynchronously, and the **--pair** option selects version 0 of the *pair* protocol instead of version 1.

- **--subscribe**=*TOPIC*

  Subscribe to *TOPIC*.  This option can only be used with the *sub* protocol. The *TOPIC* is checked against the first bytes of messages received, and messages are discarded if they do not match. This may be specified multiple times to subscribe to multiple topics. If not specified at all, then a default subscription to everything is assumed.

- **--count=**=*COUNT*

  Limit the number of iterations when looping to *COUNT* iterations. For protocols that only send, this will only send *COUNT* messages before exiting. For protocols that only receive, this will only receive *COUNT* messages before exiting. For protocols that involve a full exchange, this will only perform *COUNT* exchanges (each exchange is characterized by at most a single send, and one or more receives.) If *COUNT* is zero, then an infinite number of iterations is performed.

### Protocol Selection Options

**Note**\

At least one protocol must be selected.

- **--bus, --bus0**

  Select the *bus* version 0 protocol. This protocol can send and receive messages to and from other *bus* version 0 peers.

- **--req, --req0**

  Select the *req* version 0 protocol. This protocol sends messages to *rep* version 0 peers and receives replies from them.

- **--rep, --rep0**

  Select the *rep* version 0 protocol. This protocol receives messages from *req* version 0 peers and can send replies to them.

- **--pub, --pub0**

  Select the *pub* version 0 protocol. This protocol sends messages to *sub* version peers.

- **--sub, --sub0**

  Select the *sub* version 0 protocol. This protocol receives messages from *pub* version 0 peers, and filters them based on subscriptions set with **--subscribe**.

- **--push, --push0**

  Select the *push* version 0 protocol. This protocol sends messages to *pull* version 0 peers. A given message is normally only delivered to a single peer.

- **--pull, --pull0**

  Select the *pull* version 0 protocol. This protocol receives messages from *push* version 0 peers.

- **--pair0**

  Select the *pair* version 0 protocol. This protocol can send and receive messages with one connected *pair* version 0 peer.

- **--pair1**

  Select the *pair* version 1 protocol. This protocol can send and receive messages with one connected *pair* version 1 peer. It is not supported in **--compat** mode. (Polyamorous mode is not supported in *nngcat*, although peers may be using polyamorous mode.)

- **--pair**

  Acts as an alias for **--pair1**, unless **--compat** mode is selected, in which case it acts as an alias for **--pair0**.

- **--surveyor, --surveyor0**

  Select the *surveyor* version 0 protocol. This protocol sends a survey request to *respondent* version 0 peers, and then receives replies from them.

- **--respondent, --respondent0**

  Select the *respondent* version 0 protocol. This protocol receives survey requests from *surveyor* version 0 peers, and can send a reply to them.

### Peer Selection Options

**Note**\

At least one peer address must be selected.

**Tip**\

While legacy *nanocat* only supported one peer, *nngcat* can support more than one peer on a given connection.

- **--connect, --dial**=*URL*

  Connect to the peer at the address specified by *URL*.

- **--bind, --listen**=*URL*

  Bind to, and accept connections from peers, at the address specified by *URL*.

- **-x, --connect-ipc**=*PATH*

  Connect to the IPC path specified by *PATH*.  This is the same as **--connect**=ipc://*PATH*.

- **-X, --bind-ipc**=*PATH*

  Bind to the IPC path specified by *PATH*.  This is the same as **--bind**=ipc://*PATH*.

- **-l, --connect-local**=*PORT*

  Connect to `localhost` at the TCP port specified by *PORT*.  This is the same as **--connect**=tcp://127.0.0.1:*PORT*.

- **-L, --bind-local**=*PORT*

  Bind to the TCP port specified by *PORT*.  This is the same as **--bind**=tcp://127.0.0.1:*PORT*.

### Receive Options

Data messages received can be formatted in different ways. These options can only be specified when using a protocol that receives messages.

- **-A, --ascii**

  The same as specifying **--format**=`ascii`.

- **-Q, --quoted**

  The same as specifying **--format**=`quoted`.

- **--hex**

  The same as specifying **--format**=`hex`.

- **--msgpack**

  The same as specifying **--format**=`msgpack`.

- **--raw**

  The same as specifying **--format**=`raw`.

- **--receive-timeout**=*SEC*

  Give up receiving messages after *SEC* seconds pass without any received messages.

- **--recv-maxsz**=*COUNT*

  Set the maximum message size socket will accept to *COUNT* bytes. Messages larger than this will be discarded. The default is 1048576 (1 MB). To eliminate any restriction, use 0.

- **--format**=*FORMAT*

  Format data as indicated.  The *FORMAT* can be any of:

  `no`

  No output at all.

  `raw`

  Raw output, every byte received is sent to standard output.

  `ascii`

  ASCII safe, printable ASCII is emitted verbatim, with other bytes substituted with `.` (period).

  `quoted`

  Messages are printed as quoted strings, using C language conventions.

  `hex`

   Messages are printed as quoted strings, with every byte appearing as an escaped hexadecimal value, such as `\x2E`.

  `msgpack`

  Messages are emitted as *MessagePack* \<https://msgpack.org\> "bin format" (byte arrays).

### Transmit Options

Protocols that support sending data can use these options to select the data.

- **-D, --data**=*DATA*

  Use *DATA* for the body of outgoing messages.

- **-F, --file**=*FILE*

  Use *FILE* for the body of outgoing messages. If *FILE* is *-* the message body will be read from standard input.

- **-i, --interval**=*SEC*

  For protocols that send unsolicited data (as opposed to those that send data only in response to received messages), this will resend the outgoing message at repeating intervals of *SEC* seconds.

- **-d, --delay**=*SEC*

  Wait *SEC* seconds before sending the first outgoing message. This is useful to let connections establish before sending data, thereby avoiding message loss.

- **--send-timeout**=*SEC*

  Give up trying to send a message after *SEC* seconds.

### TLS Options

These options are only present if TLS is configured; they are ignored when using addresses that are not secured with TLS.

- **-k, --insecure**

  Skip peer validation.

- **-E, --cert**=*FILE*

  Load own certificate from *FILE*.

- **--key**=*FILE*

  Load own key from *FILE*. Should be used in conjunction with **--cert**. If not specified, and **--cert** is specified, then a single file containing both the private key and the associated certificate is assumed.

- **--cacert**=*FILE*

  Load CA certificates from *FILE*. These CAs ("Certificate Authorities") are used as trust roots when validating certificates presented by peers.

### ZeroTier Options

These options are only present if ZeroTier is configured; they are ignored otherwise.

- **--zt-home**=*DIRECTORY*

  Directory for persistent ZeroTier node (key material, etc.) This directory must already exist. Only one program may use a ZeroTier node at a time; file locking is used to prevent this.

## EXAMPLES

**Echo service using request/reply.**\

```
$ addr="tcp://127.0.0.1:4567"
$ nngcat --rep --listen=${addr} --data="42" --quoted &
$ nngcat --req --dial=${addr} --data="what is the answer?" --quoted
"what is the answer?"
"42"
```

**Send a chime every hour (3600 seconds).**\

```
$ addr=ipc:///grandpa_clock
$ nngcat --pub --listen=${addr} --data "cuckoo" --interval 3600 &
$ nngcat --sub --dial=${addr} --quoted &
"cuckoo"
```

## SEE ALSO

[libnng(3)](/libnng/3.md), [nng(7)](/nng/7.md), [nng\_bus(7)](/nng_bus/7.md), [nng\_pair(7)](/nng_pair/7.md), [nng\_pub(7)](/nng_pub/7.md), [nng\_pull(7)](/nng_pull/7.md), [nng\_push(7)](/nng_push/7.md), [nng\_sub(7)](/nng_sub/7.md), [nng\_rep(7)](/nng_rep/7.md), [nng\_req(7)](/nng_req/7.md), [nng\_respondent(7)](/nng_respondent/7.md), [nng\_surveyor(7)](/nng_surveyor/7.md)