test file1 -ef file2
たまたま手元の実装がそういう挙動だっただけなのか、違う挙動の環境もあるのかはわかりません。そもそも、由緒正しいshが標準装備しているのかも僕は情報を持っていません。ただ、Ubuntu8.04とMacOS10.5のshでも上記と同じ挙動でした。
POSIX の定義にはないですね。
Some additional primaries newly invented or from the KornShell appeared in an early proposal as part of the conditional command ( [[]]): s1 > s2, s1 < s2, str = pattern, str != pattern, f1 -nt f2, f1 -ot f2, and f1 -ef f2. They were not carried forward into the test utility when the conditional command was removed from the shell because they have not been included in the test utility built into historical implementations of the sh utility.
