Shell script to copy files

If there exist a directory,

/backup/ And the files in it are a.gz b.gz c.gz

And another directory /backup-directorybac开发者_如何学Gokup And the files in it are a.gz

I need a shells script to compare two directories if the files are present then ignore it and if the filesare not present copy it to the destination directory

Thanks..

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"rsync" command has it all

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rsync -a /backup/ /backup-directorybackup/