Hi @psdilip,
The documentation for the external data source still refers only to Terraform Enterprise since it predates the introduction of Terraform Cloud, but the warning there applies equally to both:
Warning: Terraform Enterprise does not guarantee availability of any particular language runtimes or external programs beyond standard shell utilities, so it is not recommended to use this data source within configurations that are applied within Terraform Enterprise.
There’s more information on the execution environment in Terraform Cloud’s Run Environment. There’s a link from there to a guide about installing additional software which strongly recommends against it but still includes an example of downloading jq prior to running it, relying on that jq binary being a standalone executable that doesn’t depend on any special system libraries to be available.
The external data source, due to its reliance on the surrounding execution environment, is aimed mainly at folks running Terraform CLI on their own infrastructure where they can totally control the surrounding environment. Depending on what your external bash script is intended to do, there may be other ways to get it done with Terraform that do not rely directly on external software.