Question

I’m writing a bash script which needs to, for one step, get a list of directories (variable) in a target directory (which may also contain files), and then expand them out as parameters to a python script.

Example:

/stuff/a dir/
/stuff/b other/
/stuff/c/

And I need to, within a bash script, call:

script.py "a dir/" "b other/" "c/"

or alternately, escaped spaces:

script.py a\ dir/ b\ other/ c/

I need the script to be called exactly once for directory ‘stuff’.

Is there a straightforward way to do this kind of thing? I’ve been googling around and the best I’ve managed to figure out requires me to know how many directories there are.

Answer 1

This is a job for find.

find /stuff -type d -exec script.py {} +

When you use -exec the curly braces {} are replaced with the names of the matching files, and + indicates the end of the command (in case you want to tell find to take additional actions). This is the ideal way to execute a command using find as it will handle file names with unusual characters (such as whitespace) correctly.

find is quite flexible, especially if you have the GNU version typically bundled with Linux distros.

# Don't recurse into subdirectories.
find /stuff -maxdepth 1 -type d -exec script.py {} +

# Pass in a/, b/, c/ instead of /stuff/a/, /stuff/b/, /stuff/c/.
find /stuff -type d -printf '%P\0' | xargs -0 script.py

In the second example notice the careful use of \0 and xargs -0 to use the NUL character to delimit file names. It might seem odd but this allows the command to work even if you do something really weird like use newlines \n in your directory names.

---

Alternatively, you could do this using only shell builtins. I don’t recommend this, but for educational value, here’s how:

# Start with an empty array.
DIRS=()

# For each file in /stuff/...
for FILE in /stuff/*; do
    # If the file is a directory add it to the array. ("&&" is shorthand for
    # if/then.)
    [[ -d $FILE ]] && DIRS+=("$FILE")

    # (Normally variable expansions should have double quotes to preserve
    # whitespace; thanks to bash magic we don't them inside double brackets.
    # [[ ]] has special parsing rules.)
done

# Pass directories to script. The `"${array[@]}"` syntax is an unfortunately
# verbose way of expanding an array into separate strings. The double quotes
# and the `[@]` ensure that whitespace is preserved correctly.
script.py "${DIRS[@]}"