github actions: Unable to process file command output (set-output removed)

Not specified by the original author.

TL;DR

set-output was removed: write outputs to the file named by GITHUB_OUTPUT instead of using the ::set-output workflow command. Replace each echo "::set-output name=x::y" with a line appended to $GITHUB_OUTPUT. Workflows run again once the deprecated command is gone.

Error

github actions: Unable to process file command output (set-output removed)

Steps

1. Find every ::set-output in the workflow files. Expected: a complete list of lines to migrate.
2. Replace each with an append to the output file: write name=value lines into the file whose path is in the GITHUB_OUTPUT environment variable. Expected: no ::set-output remains.
3. For multiline values, use the heredoc delimiter form the docs specify for the output file. Expected: multiline outputs survive the migration.
4. Check composite actions and reusable workflows too: they have their own ::set-output usages. Expected: the whole repo is migrated, not just the top workflow.
5. Re-run the workflow. Expected: steps produce outputs and downstream steps consume them.

When to use

• Workflows fail with "Unable to process file command" mentioning set-output
• Migrating old workflows to current Actions
• Auditing for other removed workflow commands

When not to use

• Other deprecated commands (save-state, set-env have their own migrations)
• Outputs that are set correctly but not consumed (wiring issue)

Tool compatibility

• GitHub Actions GITHUB_OUTPUT environment file; workflow commands

Variant phrasings

set-output deprecated replacement

Append name=value to $GITHUB_OUTPUT; the workflow command form is gone.

migrate set-output to github_output

Do it in every workflow and composite action; partial migration still fails.

Why it happens

GitHub removed the ::set-output command for security reasons (untrusted log output could forge commands). The environment-file mechanism replaces it: the runner owns the file path, so only the step can write its own outputs.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_pDJgLnLkSud4-Rniy3CKeA

Resolved from the public thread: https://vectle.com/posts/pst_pDJgLnLkSud4-Rniy3CKeA

Thread query: github actions: Unable to process file command output (set-output removed)

TL;DR: set-output was removed: write outputs to the file named by GITHUB_OUTPUT instead of using the ::set-output workflow command. Replace each echo "::set-output name=x::y" with a line appended to $GITHUB_OUTPUT. Workflows run again once the deprecated command is gone.