find and xargs without surprises: null-separated names, -exec + and dry runs

Goal

Select files by name, type, age or size and run a command on them in a way that cannot break on unusual file names and cannot act on the wrong set.

Prerequisites

GNU findutils or another implementation with -print0 and xargs -0. Awareness that find evaluates its arguments as one expression from left to right.

Steps

1. Write the selection first and only print it: find . -type f -name '*.log' -mtime +30 -print. Read the list. -maxdepth 1 limits depth; -path ./node_modules -prune -o -type f -print skips a subtree.
2. Choose how to run the command. For one command over many files, use -exec cmd {} +: the man page says the command line is built by appending names, like xargs, so there are far fewer invocations than with -exec cmd {} \;, which runs once per file. -execdir runs the command from the file's directory; the man page recommends it over -exec for security reasons.
3. When another program must consume the names, separate them with NUL: find ... -print0 | xargs -0 cmd. The xargs page explains that its default separators (blanks and newlines, with quotes and backslashes special) mishandle names containing them, while -0 takes every byte literally.
4. Add -r (--no-run-if-empty) to xargs. Without it, the man page states, the command runs once even when there is no input, which for some commands means "everything".
5. Use -I{} when the name must appear mid-command (it implies one item per invocation), -n 1 for one item at a time, and -P 4 with -n for parallel runs.
6. Before destructive actions, put echo in front of the command or keep -print; then replace -print with -delete. The man page warns that -delete written first deletes everything below the starting points, and that it switches on -depth, which makes -prune ineffective.
7. Check exit statuses: xargs returns 123 if any invocation failed, 124 if a command exited with 255 (which also stops xargs), 126 or 127 if the command could not be run or found.

Expected result

A command line that handles any file name, runs the tool as few times as needed, does nothing when the selection is empty, and was reviewed as a listing before it touched anything.

Limits and test basis

Behaviour follows the cited GNU man pages; the xargs page states that -0 and -r joined POSIX only in its 2024 edition, and -delete and -execdir are not POSIX, so other implementations may lack them. Both -exec ... + and xargs split long lists into several invocations, so the command must be safe to run in batches. No timings are claimed.

Dry runs that match the deletion

-delete implies -depth, and with -depth the -prune action has no effect, so a selection previewed with -prune ... -print and then executed with -delete deletes inside the pruned subtree as well. Preview and execution must use the same traversal. Either add -depth to the preview and replace the prune with a test that does not select the subtree (find . -depth -not -path './node_modules/*' -name '*.log' -print, then the same with -delete), or keep -prune and delete through a pipe: find . -path ./node_modules -prune -o -name '*.log' -print0 | xargs -0r rm --. Whichever form is chosen, run it once with -print or with echo rm in front and compare the list before running it for real.