I copy/paste from a previous post. "Exoteric" is a stretch (in particular, because there are no alternative glue languages, if we exclude all the shell variants), but cryptic, unintuitive and error-prone fits well.

Arrays:

  - `${#myvar[@]}`: unreadable

  - `mapfile myvar < <(grep pattern file)`: "mapfile" is not exactly a clear term (there's the synonym
    "readarray", but "mapfile" is the reference; worse, you may find both used inconsistently); the
    command as I wrote it also has two problems

Strings:

  - `${myvar##.*}`: unreadable

  - `echo $(IFS=,; echo "${myvar[*]}")`: unreadable; most also don't know the difference between `[@]`
    and `[*]`; this doesn't also work for two-char join operations

  - `[[ $myvar =~ $(echo '\bpattern\b') ]]`: unreadable, and most don't know why command substitution
    is needed

Redirections:

  - `3>&2 2>&1 1>&3`: most don't know what this means