If "unset" claims that "all" attributes are reset, then that would mean that some attribute that most of us have never heard of (the "null on weekends" attribute) must be reset by the "unset" command - yet the shell that invented that attribute might not act that way, and perhaps for good reason.

With all of this, everyone should also note that being readonly does not (in any shell I can test) prevent the "export" attribute from being set, it just stops "unset" from clearing it. There's no reason a shell that provides some other way (than unset) from removing the export attribute cannot allow that other mechanism to remove "export" from a readonly variable (all of that is beyond the standard however - but the standard must not prohibit any of this.)

readonly foo
export foo
if [ "$YASH_VERSION" ]
then
    typeset -X foo
else
    typeset +x foo
fi

The unset utility shall unset a variable or function definition specified by each name operand, as follows:

• If −v is specified, name refers to a variable. If the named variable exists and does not have the readonly attribute, the shell shall unset it and shall remove the export attribute if the variable has it. Read-only variables cannot be unset.


• If −f is specified, name refers to a function. If the named function exists, the shell shall unset the function definition.


• If neither −f nor −v is specified and name refers to a variable that exists, the variable shall be unset as if -v was specified; if a variable by that name does not exist, it is unspecified whether a function by that name, if any, is unset.

All name operands were successfully unset.

Each name operand either did not exist or was successfully unset.