Compatibility risks

tail

• Obsolete numeric option: tail -1 (without -n) is a GNU-accepted historical shorthand. Some uutils/coreutils releases did not accept this shorthand.

• Concatenated form: tail -n+2 (no space) is accepted by GNU tail; uutils tail historically required the POSIX form with a space (tail -n +2). Newer uutils likely accept both.

head

• head -n 1 is standard and supported by both GNU and Rust coreutils. GNU also accepts the historical shorthand head -1 (without -n); uutils historically did not accept the obsolete numeric form in some releases.

The flow script and Makefile use -n1, so it’s fine. test.butt combines head -n1 (without space) with head -13 etc. (without -n).

Command line argument parsing in uutils

The uutils coreutils project (which includes utilities like uu_head and uu_tail) does use the clap crate for command-line argument parsing. The option -1 (and similarly -2, -3, …) is treated as a legacy POSIX/GNU shortcut, meaning:

-<number> ≡ -n <number>

This behavior is implemented intentionally in the parse_obsolete function in uucore where the digit options are intercepted and translated into -n, not provided automatically by clap. One may expect obsolete and legacy code removed in a future release.

Suggestions

• Use tail -n 1 (with space) and tail -n +2 (with space) for maximum portability across uutils versions.
• Prefer head -n 13 (with space) across all files for consistency and maximum portability.