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77 lines
2.1 KiB
Markdown
77 lines
2.1 KiB
Markdown
# System Operators
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The `system` operator allows you to run an external command and use its output as a value in your expression.
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**Security warning**: The system operator is disabled by default. You must explicitly pass `--security-enable-system-operator` to use it.
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**Note:** When enabled, the system operator can replicate the functionality of `env` and `load`
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operators via external commands. Enabling it effectively overrides `--security-disable-env-ops`
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and `--security-disable-file-ops`.
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## Usage
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```bash
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yq --security-enable-system-operator --null-input '.field = system("command"; "arg1")'
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```
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The operator takes:
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- A command string (required)
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- An argument (or an array of arguments), separated from the command by `;` (optional)
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The current matched node's value is serialised and piped to the command via stdin. The command's stdout (with trailing newline stripped) is returned as a string.
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## Disabling the system operator
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The system operator is disabled by default. When disabled, an error is returned instead of running the command, consistent with `--security-disable-env-ops` and `--security-disable-file-ops`.
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Use `--security-enable-system-operator` flag to enable it.
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## system operator returns error when disabled
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Use `--security-enable-system-operator` to enable the system operator.
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Given a sample.yml file of:
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```yaml
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country: Australia
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```
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then
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```bash
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yq '.country = system("/usr/bin/echo"; "test")' sample.yml
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```
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will output
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```bash
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Error: system operations are disabled, use --security-enable-system-operator to enable
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```
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## Run a command with an argument
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Use `--security-enable-system-operator` to enable the system operator.
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Given a sample.yml file of:
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```yaml
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country: Australia
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```
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then
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```bash
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yq --security-enable-system-operator '.country = system("/usr/bin/echo"; "test")' sample.yml
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```
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will output
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```yaml
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country: test
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```
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## Run a command without arguments
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Omit the semicolon and args to run the command with no extra arguments.
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Given a sample.yml file of:
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```yaml
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a: hello
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```
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then
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```bash
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yq --security-enable-system-operator '.a = system("/usr/bin/echo")' sample.yml
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```
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will output
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```yaml
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a: ""
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```
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