Transforming Output

ProcessRunOptions.TransformOutput and ProcessRunOptions.TransformError are optional per-line hooks applied to stdout and stderr respectively, before each line is logged and captured.

Each delegate has the shape Func<string, string?>:

It receives the raw line (never null — null data events are filtered out beforehand).
Return the same string to pass the line through unchanged.
Return a different string to rewrite the line.
Return null to suppress the line entirely — it is neither logged nor included in ProcessRunResult.Output / ProcessRunResult.Error.

Redacting secrets

var options = new ProcessRunOptions("deploy", "--token " + token)
{
    TransformOutput = line => line.Contains(token)
        ? line.Replace(token, "[redacted]")
        : line,
};

The redaction applies to both the live log stream and the captured result.Output.

Warning

Transforms only see the process's output lines. The invocation line (Run: deploy --token …) is logged before the process starts and includes the full arguments (environment variables are logged by name only), so a secret passed on the command line still reaches the log at InvocationLogLevel. See Logging.

Filtering noise

Drop high-volume progress lines that would otherwise flood the logs and the captured output:

var options = new ProcessRunOptions("docker", "build .")
{
    TransformError = line => line.StartsWith("#") || line.Contains("DONE")
        ? null   // suppressed: not logged, not captured
        : line,
};

Normalizing output

Transforms can also reshape lines for downstream parsing:

var options = new ProcessRunOptions("git", "status --porcelain")
{
    TransformOutput = line => line.TrimEnd(),
};

Behavioral notes

Transforms run on the process's output-reader callbacks, once per line, as lines arrive. Keep them fast and side-effect-free.
A suppressed line is excluded from failure promotion too — if the process fails, the re-logged "full output" is the captured (post-transform) output.
Transforms are per-invocation. For a shared policy, build a helper that returns pre-configured ProcessRunOptions instances, or wrap the delegate in a reusable method.

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