gcloud storage objects compose

INFORMATION
gcloud storage objects compose is supported in universe domain universe; however, some of the values used in the help text may not be available. Command examples may not work as-is and may requires changes before execution.
NAME
gcloud storage objects compose - concatenate a sequence of objects into a new composite object
SYNOPSIS
gcloud storage objects compose SOURCE [SOURCE …] DESTINATION [--additional-headers=HEADER=VALUE] [--clear-custom-contexts     | --custom-contexts=[CUSTOM_CONTEXTS_KEYS_AND_VALUES,…]     | --custom-contexts-file=CUSTOM_CONTEXTS_FILE] [--if-generation-match=GENERATION --if-metageneration-match=METAGENERATION] [--retain-until=DATETIME --retention-mode=RETENTION_MODE] [GCLOUD_WIDE_FLAG …]
DESCRIPTION
gcloud storage objects compose creates a new object whose content is the concatenation of a given sequence of source objects in the same bucket. For more information, please see: composite objects documentation.

There is a limit (currently 32) to the number of components that can be composed in a single operation.

EXAMPLES
The following command creates a new object target.txt by concatenating a.txt and b.txt: 
gcloud storage objects compose gs://bucket/a.txt gs://bucket/b.txt gs://bucket/target.txt

Contexts are merged from source objects on the composed object by default. However, the following command overwrites custom contexts on composed object: 

gcloud storage objects compose gs://bucket/a.txt gs://bucket/b.txt gs://bucket/target.txt --custom-contexts=key1=value1,key2=value2
POSITIONAL ARGUMENTS
SOURCE [SOURCE …]
The list of source objects that will be concatenated into a single object.
DESTINATION
The destination object.
FLAGS
--additional-headers=HEADER=VALUE
Includes arbitrary headers in storage API calls. Accepts a comma separated list of key=value pairs, e.g. header1=value1,header2=value2. Overrides the default storage/additional_headers property value for this command invocation.
OBJECT CONTEXTS FLAGS
Group that allow users to handle object contexts.

At most one of these can be specified:

--clear-custom-contexts
Clears all custom contexts on objects.
--custom-contexts=[CUSTOM_CONTEXTS_KEYS_AND_VALUES,…]
Sets custom contexts on objects. The existing custom contexts (if any) would be overwritten.
--custom-contexts-file=CUSTOM_CONTEXTS_FILE
Path to a local JSON or YAML file containing custom contexts one wants to set on an object. For example:

1. The following JSON document shows two key value pairs, i.e. (key1, value1) and (key2, value2): 

  {
    "key1": {"value": "value1"},
    "key2": {"value": "value2"}
  }

2. The following YAML document shows two key value pairs, i.e. (key1, value1) and (key2, value2): 

  key1:
    value: value1
  key2:
    value: value2

Note: Currently object contexts only supports string format for values.

PRECONDITION FLAGS
--if-generation-match=GENERATION
Execute only if the generation matches the generation of the requested object.
--if-metageneration-match=METAGENERATION
Execute only if the metageneration matches the metageneration of the requested object.
RETENTION FLAGS
--retain-until=DATETIME
Ensures the destination object is retained until the specified time in RFC 3339 format.
--retention-mode=RETENTION_MODE
Sets the destination object retention mode to either "Locked" or "Unlocked". When retention mode is "Locked", the retain until time can only be increased. RETENTION_MODE must be one of: Locked, Unlocked.
GCLOUD WIDE FLAGS
These flags are available to all commands: --access-token-file, --account, --billing-project, --configuration, --flags-file, --flatten, --format, --help, --impersonate-service-account, --log-http, --project, --quiet, --trace-token, --user-output-enabled, --verbosity.

Run $ gcloud help for details.

NOTES
This variant is also available: 
gcloud alpha storage objects compose