Last updated on August 20, 2020 by Dan Nanni
scp
command. In this case, I want to skip existing files, so that they will not get overwritten by scp
. But the scp
command would blindly overwrite existing files if the same name files exist at either host. How can I copy files over without overwriting existing files, so that only new files are downloaded (or uploaded) by scp
?Suppose you have a list of files on a remote host, some of which already exist locally. What you want is to transfer only those files that are not found locally. If you blindly run scp
with wildcard, it would fetch all remote files (existing as well as non-existing files), and overwrite existing local files. You want to avoid this.
In another similar situation, you may want to upload local files to a remote site, but without replacing any remote files.
Here are a few ways to skip existing files when transferring files with scp
.
rsync
If the local and remote hosts have rsync
installed, using rsync
will be the easiest way to copy only new files over, since rsync
is designed for incremental/differential backups.
In this case, you need to explicitly tell rsync
to skip any existing files during sync. Otherwise, rsync
will try to use file modification time to sync two hosts, which is not what you want.
To download all remote files (over SSH) while skipping existing local files:
$ rsync -av --ignore-existing user@remote_host:/path/to/remote/directory/* /path/to/local/directory/
Similarly, to upload all local files (over SSH) without overwriting any duplicate remote files:
$ rsync -av --ignore-existing /path/to/local/directory/* user@remote_host:/path/to/remote/directory/
getfacl
/setfacl
Another way to scp only new files over to a destination is by leveraging file permissions. More specifically, what you can do is to make all destination files "read-only" before scp
transfer. This will prevent any existing destination files from being overwritten by scp
. After scp
transfer is completed, restore the file permissions to the original state. The ACL command-line tools (getfacl
and setfacl
) come in handy when you temporarily change file permissions and restore them.
Here is how to scp
files without replacing existing files using ACL tools.
To download all remote files (over SSH) while skiping existing local files:
$ cd /path/to/local/directory $ getfacl -R . > permissions.txt $ chmod -R a-w . $ scp -r user@remote_host:/path/to/remote/directory/* . $ setfacl --restore=permissions.txt
Similarly, to upload all local files without replacing any remote file, first back up the file permissions of the remote destination folder. Then remove write-permission from all files in the remote destination folder. Finally, upload all local files, and then restore the saved file permissions.
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