Ran into a situation where I needed to replace certain files in a directory tree with files from a similarly shaped directory tree. The other files in each tree needed to remain untouched. Below is an example of the directory structure.

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root-dir
├── target-dir
│   ├── 20121230
│   │   ├── data.csv
│   │   └── instruments.csv
│   └── 20121231
│       ├── data.csv
│       └── instruments.csv
└── other-dir
    ├── 20121230
    │   ├── data.csv
    │   └── instruments.csv
    └── 20121231
        ├── data.csv
        └── instruments.csv

Goal is to copy instruments.csv from the sub-directories of other-dir to the matching sub-directories of target-dir. In the past I’ve solved this by being in the other-dir directory and banging out a for loop at the command line (other-dir$ is the bash prompt).

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other-dir$ for d in $(ls); do cp $d/instruments.txt ../target-dir/$d/; done

One feature (or issue) with this approach is that if a sub-directory exists in other-dir but not in target-dir that sub-directory will not be created in target-dir.

I took a bit of time to explore other ways of accomplishing this task and stopped after coming up with two additional ways.

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other-dir$ find . -name "instruments.txt" | xargs -I {} cp {} ../target-dir/{}

The above is basically the same as the first solution. It uses find to generate the list of files and then constructs cp commands. It also doesn’t create sub-directories in target-dir.

The next example has different behavior from the above cp solutions. Like the second solution, it generates a list of files to copy using find but then uses rsync with the --files-from flag to mirror those files under target-dir. Unlike the cp based solutions, sub-directories of other-dir that do not exist in target-dir will be created.

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other-dir$ find . -name "instruments.txt" | rsync --files-from=- . ../target-dir

I’m sure there are many more ways of accomplishing this task. Figuring out the three above was enough for me. They are fairly straight forward and don’t depend on esoteric command line flags. The solution I use in the future will depend on whether or not I need sub-directories created in the target directory.