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Comments on How to list the first x files in each directory

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How to list the first x files in each directory

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MWE

With the following tree:

l1
└── l2
    ├── d0
    │   ├── f0
    │   ├── f1
    │   ├── f2
    │   ├── f3
    │   ├── f4
    │   └── f5
    ├── d1
    │   ├── f0
    │   ├── f1
    │   ├── f2
    │   ├── f3
    │   ├── f4
    │   └── f5
    ├── d2
    │   ├── f0
    │   ├── f1
    │   ├── f2
    │   ├── f3
    │   ├── f4
    │   └── f5
    ├── d3
    │   ├── f0
    │   ├── f1
    │   ├── f2
    │   ├── f3
    │   ├── f4
    │   └── f5
    ├── d4
    │   ├── f0
    │   ├── f1
    │   ├── f2
    │   ├── f3
    │   ├── f4
    │   └── f5
    └── d5
        ├── f0
        ├── f1
        ├── f2
        ├── f3
        ├── f4
        └── f5

8 directories, 36 files

created by this script:

#!/bin/bash

path=l1/l2

mkdir -p $path

for dir in {0..5}; do
    mkdir $path/d$dir

    for file in {0..5}; do
        touch $path/d$dir/f$file
    done
done

Problem

How do I list the first three files of each directory?

First three being the first three alphabetically sorted.

Desired output:

l1/l2/d0/f0
l1/l2/d0/f1
l1/l2/d0/f2
l1/l2/d1/f0
l1/l2/d1/f1
l1/l2/d1/f2
l1/l2/d2/f0
l1/l2/d2/f1
l1/l2/d2/f2
l1/l2/d3/f0
l1/l2/d3/f1
l1/l2/d3/f2
l1/l2/d4/f0
l1/l2/d4/f1
l1/l2/d4/f2
l1/l2/d5/f0
l1/l2/d5/f1
l1/l2/d5/f2

Tried

I can get each file via:

find l1 -mindepth 3 -maxdepth 3 -type f

but I can't find a way in the manual to specify the match depth.

The output from find is also unsorted, and so, the first three would not be the first three alphabetically.

Notes

My goal is to make a trimmed copy of a large dataset for preliminary, quick testing as I develop my code. Performing this trim within the code unnecessarily complicates the test code and will be a wasted effort as it will be removed for the real deal. Without it in place, I am able to test what will be the final product.

The real target using the real dataset may be sub directories and not files. In other words, "give me the the first 3 directories in level 2".

Ideally, if I can find a way to list the files, I can pipe them to a cp command.

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Is this what you want?

Edit: Credit to Kamil Maciorowski‭ for catching an unsafe interpolation in the previous draft; it will work for non-adversarial inputs but this newer version is safer and a better example to learn from.

find l1 -mindepth 2 -maxdepth 2 \
  -type d \! -empty \ 
  -exec sh -c 'printf "%s\n" "$1"/* | head -n 3' _ {} \;
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4 comment threads

Never embed `{}` in shell code (1 comment)
Questions (3 comments)
Potential simplifications (4 comments)
Works for me (1 comment)
Potential simplifications
mcp‭ wrote 7 months ago

This works, thank you! I did not need \! -empty. I was thinking there might be a way without printf using execdir.

mcp‭ wrote 7 months ago

find l1 -mindepth 2 -maxdepth 2 -exec sh -c "ls '{}'/* | head -n 3" \; also works! Thanks for pointing me in the right direction.

mcp‭ wrote 7 months ago

Actually the 'printfis useful for larger datasets wherels` starts grouping by directory and excluding the full path.

r~~‭ wrote 7 months ago

The \! -empty is there because if the shell expands a wildcard that doesn't match anything, the wildcard remains, and you don't want .../empty_dir/* in your output.

The ls is an unnecessary subprocess invocation. sh is already expanding the * before ls is invoked.