The correct option is echo.

In GitHub Actions you publish a step output by appending a line in the form name equals value to the file referenced by the GITHUB_OUTPUT environment variable. You achieve this with echo by running echo "build_id=12345" >> "$GITHUB_OUTPUT". Downstream steps can then read the value through the outputs of the step.

export only updates environment variables in the current shell and it does not create a step output that other steps can read.

set changes shell options or positional parameters and it does not write to the special file that GitHub Actions uses for outputs. Do not confuse it with the old workflow command that used to set outputs because that approach is deprecated and no longer recommended.

printf can print text but it does not by itself create a step output in GitHub Actions. The documented and expected method is to use echo to append the name and value to the GITHUB_OUTPUT file.

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