Gnu/coreutils/Conditional-Executability
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27.2.4 Conditional Executability
There is one more special type of symbolic permission: if you use
‘X
’ instead of ‘x
’, execute/search permission is affected only if the
file is a directory or already had execute permission.
For example, this mode:
a+X
gives all users permission to search directories, or to execute files if anyone could execute them before.