unlink is as specified in the Single UNIX Specification, Version 2, but with differences as listed below.
See also Additional behaviors: unlink/link on directory>.
If path specifies a directory, the implementation may return EISDIR instead of EPERM as specified by Single UNIX Specification, Version 2. [1]
| [1] | The Linux kernel has deliberately chosen EISDIR for this case and does not expect to change (Al Viro, personal communication). |