# jsonwatch — like `watch -d`, but for JSON
jsonwatch is a command-line utility that lets you track changes in JSON data delivered by a command or a web (HTTP/HTTPS) API.
jsonwatch requests data from the source repeatedly at a set interval.
It displays the differences when the data changes.
It is similar but not identical to how [watch(1)](https://manpages.debian.org/stable/procps/watch.1.en.html) with the `-d` switch works for plain text.
jsonwatch has been tested on Debian 12, Ubuntu 24.04, macOS 14, and Windows 10 and Server 2022.
The two previous versions of jsonwatch are preserved in the branch
[`python`](https://github.com/dbohdan/jsonwatch/tree/python)
and
[`haskell`](https://github.com/dbohdan/jsonwatch/tree/haskell).
## Installation
Prebuilt binaries are available for Linux (x86_64) and Windows (x86).
Binaries are attached to releases on the
["Releases"](https://github.com/dbohdan/jsonwatch/releases)
page.
### Installing with Cargo
```shell
cargo install jsonwatch
```
### Building on Debian and Ubuntu
Follow the instructions to build a static Linux binary of jsonwatch from the source code on recent Debian and Ubuntu.
1. Install [Rustup](https://rustup.rs/).
Through Rustup, add the stable musl libc target for your CPU.
```shell
rustup target add x86_64-unknown-linux-musl
```
2. Install the build and test dependencies.
Building requires [just](https://github.com/casey/just) 1.39 or later.
```shell
sudo apt install build-essential expect musl-tools
cargo install just
```
3. Clone this repository.
Build the binary.
```shell
git clone https://github.com/dbohdan/jsonwatch
cd jsonwatch
just test
just release-linux
```
### Cross-compiling for Windows
Follow the instructions to build a 32-bit Windows binary of jsonwatch on recent Debian and Ubuntu.
1. Install [Rustup](https://rustup.rs/).
Through Rustup, add the i686 GNU ABI Windows target.
```shell
rustup target add i686-pc-windows-gnu
```
2. Install the build dependencies.
Building requires [just](https://github.com/casey/just) 1.39 or later.
```shell
sudo apt install build-essential mingw-w64
cargo install just
```
3. Configure Cargo for cross-compilation.
Add the following to `~/.cargo/config`.
```toml
[target.i686-pc-windows-gnu]
linker = "/usr/bin/i686-w64-mingw32-gcc"
```
4. Clone this repository.
Build the binary.
```shell
git clone https://github.com/dbohdan/jsonwatch
cd jsonwatch
just release-windows
```
## Usage
You must run jsonwatch with a subcommand.
jsonwatch processes valid JSON.
The following behavior applies:
- If the data source (command or URL) produces an error (non-zero exit status or HTTP failure response), the stored data remains unchanged
- Responses with invalid JSON do not update the stored data
- An empty response (no data or whitespace only) sets stored data to empty, potentially causing a change
Some security measures are in place:
- Input data (command output or HTTP response body) printed with `-vv` has any control characters escaped to prevent display issues and security risks like ANSI escape sequence injection.
Command output is also escaped because commands that access remote data sources are expected.
- URL responses are limited to 128 MiB
- Command output is not limited in size and is buffered in memory
Control characters are escaped as follows:
| Newline (`\n`) | Passed through | `"A\nB"` → `"A\nB"` |
| Tab (`\t`) | Passed through | `"A\tB"` → `"A\tB"` |
| Carriage return (`\r`) | `\u{d}` | `"A\rB"` → `"A\u{d}B"` |
| Escape (`\x1b`) | `\u{1b}` | `"\x1b[32m"` → `"\u{1b}[32m"` |
| Other control chars | `\u{xx}` | ASCII BEL (`\x07`) → `"\u{7}"` |
Non-control characters are printed as is.
### Global options
```none
Track changes in JSON data
Usage: jsonwatch [OPTIONS] <COMMAND>
Commands:
cmd Execute a command and track changes in the JSON output
url Fetch a URL and track changes in the JSON data
help Print this message or the help of the given subcommand(s)
Options:
-D, --no-date Don't print date and time for each diff
-I, --no-initial-values Don't print initial JSON values
-c, --changes <count> Exit after a number of changes
-n, --interval <seconds> Polling interval in seconds [default: 2]
-v, --verbose... Verbose mode ('-v' for errors, '-vv' for input data
and errors)
-h, --help Print help
-V, --version Print version
```
### `cmd` subcommand
You can use `cmd` or `command` as the name of the subcommand.
```none
Execute a command and track changes in the JSON output
Usage: jsonwatch cmd <command> [arg]...
Arguments:
<command> Command to execute
[arg]... Arguments to the command
Options:
-h, --help Print help
```
### `url` subcommand
```none
Fetch a URL and track changes in the JSON data
Usage: jsonwatch url [OPTIONS] <url>
Arguments:
<url> URL to fetch
Options:
-A, --user-agent <user-agent> Custom User-Agent string [default: curl/7.58.0]
-H, --header <header> Custom headers in the format "X-Foo: bar"
-h, --help Print help
```
## Use examples
### Command
#### Testing jsonwatch
This example uses the POSIX shell to generate random JSON test data.
```none
$ jsonwatch -n 1 cmd sh -c "echo '{ \"filename\": \"'\$(mktemp -u)'\"}'"
{
"filename": "/tmp/tmp.dh3Y7LJTaK"
}
2020-01-19T18:52:19+0000 .filename: "/tmp/tmp.dh3Y7LJTaK" -> "/tmp/tmp.i4s56VENEJ"
2020-01-19T18:52:20+0000 .filename: "/tmp/tmp.i4s56VENEJ" -> "/tmp/tmp.zzMUSn45Fc"
2020-01-19T18:52:21+0000 .filename: "/tmp/tmp.zzMUSn45Fc" -> "/tmp/tmp.Jj1cKt6VLr"
2020-01-19T18:52:22+0000 .filename: "/tmp/tmp.Jj1cKt6VLr" -> "/tmp/tmp.1LGk4ok8O2"
2020-01-19T18:52:23+0000 .filename: "/tmp/tmp.1LGk4ok8O2" -> "/tmp/tmp.wWulyho8Qj"
```
#### Docker
The command in this example tracks Docker process information when you have a single running container.
```none
$ jsonwatch -n 1 command docker ps -a "--format={{json .}}"
2020-01-19T18:57:20+0000
+ .Command: "\"bash\""
+ .CreatedAt: "2020-01-19 18:57:20 +0000 UTC"
+ .ID: "dce7fb2194ed"
+ .Image: "i386/ubuntu:latest"
+ .Labels: ""
+ .LocalVolumes: "0"
+ .Mounts: ""
+ .Names: "dreamy_edison"
+ .Networks: "bridge"
+ .Ports: ""
+ .RunningFor: "Less than a second ago"
+ .Size: "0B"
+ .Status: "Created"
2020-01-19T18:57:21+0000 .RunningFor: "Less than a second ago" -> "1 second ago"
2020-01-19T18:57:23+0000
.RunningFor: "1 second ago" -> "3 seconds ago"
.Status: "Created" -> "Up 1 second"
2020-01-19T18:57:24+0000
.RunningFor: "3 seconds ago" -> "4 seconds ago"
.Status: "Up 1 second" -> "Up 2 seconds"
2020-01-19T18:57:25+0000
.RunningFor: "4 seconds ago" -> "5 seconds ago"
.Status: "Up 2 seconds" -> "Up 3 seconds"
```
For multiple running containers, you will need a more complex jsonwatch command.
The command needs to transform the [JSON Lines](https://jsonlines.org/) output into a single JSON document.
For example, it can be the following command with the POSIX shell and [jq](https://en.wikipedia.org/wiki/Jq_(programming_language)):
```shell
#### `cmd.exe` on Windows
This example is a simple test on Windows.
We start watching the output of a `cmd.exe` command, then manually edit the file the command prints and are shown the changes.
```none
> jsonwatch command cmd.exe /c "type tests\weather1.json"
{
"clouds": {
"all": 92
},
"name": "Kiev",
"coord": {
"lat": 50.43,
"lon": 30.52
},
"sys": {
"country": "UA",
"message": 0.0051,
"sunset": 1394985874,
"sunrise": 1394942901
},
"weather": [
{
"main": "Snow",
"id": 612,
"icon": "13d",
"description": "light shower sleet"
},
{
"main": "Rain",
"id": 520,
"icon": "09d",
"description": "light intensity shower rain"
}
],
"rain": {
"3h": 2
},
"base": "cmc stations",
"dt": 1394979003,
"main": {
"pressure": 974.8229,
"humidity": 91,
"temp_max": 277.45,
"temp": 276.45,
"temp_min": 276.15
},
"id": 703448,
"wind": {
"speed": 10.27,
"deg": 245.507
},
"cod": 200
}
2020-01-19T18:51:04+0000 + .test: true
2020-01-19T18:51:10+0000 .test: true -> false
2020-01-19T18:51:23+0000 - .test: false
```
### URL
#### Weather tracking
The API in this example no longer works without a key.
```none
$ jsonwatch --no-initial-values -n 300 url 'http://api.openweathermap.org/data/2.5/weather?q=Kiev,ua'
2014-03-17T23:06:19+0200
+ .rain.1h: 0.76
- .rain.3h: 0.5
.dt: 1395086402 -> 1395089402
.main.temp: 279.07 -> 278.66
.main.temp_max: 279.82 -> 280.15
.main.temp_min: 277.95 -> 276.05
.sys.message: 0.0353 -> 0.0083
```
#### Geolocation
Try this on a mobile device.
```none
$ jsonwatch -I -n 300 url https://ipinfo.io/
```
## License
jsonwatch is distributed under the MIT license.
See the file [`LICENSE`](LICENSE) for details.
[Wapp](tests/vendor/wapp/wapp.tcl) is copyright (c) 2017 D. Richard Hipp and is distributed under the Simplified BSD License.