curl/docs/cmdline-opts/etag-save.md

c	SPDX-License-Identifier	Long	Arg	Help	Protocols	Added	Category	Multi	See-also	Example
Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.	curl	etag-save	<file>	Parse incoming ETag and save to a file	HTTP	7.68.0	http	single	etag-compare	--etag-save storetag.txt $URL

--etag-save

Save an HTTP ETag to the specified file. An ETag is a caching related header, usually returned in a response. Use this option with a single URL only.

If no ETag is sent by the server, an empty file is created.

In many situations you want to use an existing etag in the request to avoid downloading the same resource again but also save the new etag if it has indeed changed, by using both etag options --etag-save and --etag-compare with the same filename, in the same command line.

Starting in curl 8.12.0, using the --create-dirs option can also create missing directory components for the path provided in --etag-save.