Environment variables

Written by the action

Variable	When	Value
PATH	Always	The CLI's tool cache directory is prepended.
FME_CONFIG_DIR	Always	The config-dir input, default ${RUNNER_TEMP}/filemoverexpress. File Mover Express reads its config from here and writes all of its state here.
AWS_REGION	bucket is set, a region resolved, and both region variables are unset	The resolved region.
AWS_DEFAULT_REGION	Same as AWS_REGION	The resolved region.

The action exports the region pair only when neither is set, so it never overwrites what configure-aws-credentials or your workflow exported. It never writes credential variables.

NOTE

Upstream documentation names the config directory variable filemoverexpress_CONFIG_DIR. The CLI actually reads FME_CONFIG_DIR.

Read by the action

Variable	Used for
AWS_REGION	Region for the transfer profile when region is empty.
AWS_DEFAULT_REGION	Region when region and AWS_REGION are empty.
AWS_PROFILE	Choosing which profile's region to read from the AWS config file when aws-profile is empty.
AWS_CONFIG_FILE	Location of the AWS config file. Default ~/.aws/config.
AWS_ACCESS_KEY_ID, AWS_WEB_IDENTITY_TOKEN_FILE	Only checked for presence, to add a hint to the error when validate-credentials fails.
RUNNER_TEMP	Default parent of config-dir.
RUNNER_TOOL_CACHE	Tool cache root.
GITHUB_WORKSPACE	Base for a relative filemoverexpress-version-file.

Read by File Mover Express at transfer time

The action doesn't touch these. The CLI's AWS SDK for Go v2 reads them every time a command runs:

Variable	Set by	Purpose
AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_SESSION_TOKEN	configure-aws-credentials (default mode)	Session credentials.
AWS_PROFILE	configure-aws-credentials (aws-profile mode)	Named profile, when the transfer profile has no profile key.
AWS_SHARED_CREDENTIALS_FILE, AWS_CONFIG_FILE	You, optionally	Locations of the shared AWS files.
AWS_ROLE_ARN, AWS_WEB_IDENTITY_TOKEN_FILE	You, optionally	Web identity federation.
AWS_ENDPOINT_URL_S3, AWS_ENDPOINT_URL	You, optionally	Endpoint override when the transfer profile has no endpoint.
FME_CONFIG_DIR	This action	Config and state directory.

Credentials and interop explains the order the SDK checks these in.