[bug #38474] Unintended (?) behaviour change of -perm +mode predicate

[Ludovic Brenta]

Follow-up Comment #4, bug #38474 (project findutils):

James, the clause of the POSIX standard you mention is not relevant to this
case because the mode was given in octal, not symbolic form.  The relevant
clause is:

-perm [-]onum
    If the hyphen is omitted, the primary shall evaluate as true when the file
permission bits exactly match the value of the octal number onum and only the
bits corresponding to the octal mask 07777 shall be compared. (See the
description of the octal mode in chmod().) Otherwise, if onum is prefixed by a
hyphen, the primary shall evaluate as true if at least all of the bits
specified in onum that are also set in the octal mask 07777 are set.

I take this to mean that "-perm +0100" is in fact unspecified.  Thus:

"-perm u+x", "-perm u=x" and "-perm 0100" match if and only if the file
permissions are exactly --x------.

"-perm +u+x" and "-perm -0100" match if the file permissions are anything of
the form ??x??????.

"-perm +0100" is unspecified and, as far as I understand, a syntax error. 
Presumably, find should reject such an argument.

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