Revert "learn test 3 union it should run on unix system"

This reverts commit 57cb58dc817defe46a34930981d33b1b3dfccd90.
Revert "Revert "learn test 3 union it should run on unix system""

This reverts commit 9104d7ce69ea940a20d52988065adc74f07ddc54.
bash: m-f: 未找到命令
Revert "Revert "Revert "learn test 3 union it should run on unix system"""

This reverts commit b2290ff52b7862ca11f54b03ce0d498a07528d45.
Revert "bash: m-f: 未找到命令"

This reverts commit ab8404a3f5a0bc6b9e6bcfc1a8f3aa5bb847f46e.
Revert "Revert "bash: m-f: 未找到命令""

This reverts commit 0d937d4dd990ce4ab3445191b937f77d3c944228.