1、
root@PC1:/home/test# ls root@PC1:/home/test# for i in {A..D}; do for j in {A..D}; do echo $i"_"$j; done; done ## 生成A-D任意的两两组合 A_A A_B A_C A_D B_A B_B B_C B_D C_A C_B C_C C_D D_A D_B D_C D_D
2、
root@PC1:/home/test# ls root@PC1:/home/test# for i in {A..D}{A..D}; do echo $i; done AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DD
参考：https://mp.weixin.qq.com/s?__biz=MzA4NzQzMzU4Mg==&mid=2652979038&idx=2&sn=ce399516779f83a53fdba74d383be9e0&chksm=8bec175fbc9b9e495f5935a2b4efdcbeff2fbca3d2145f87ee6acc7ef6a0220f0e2718d2aef0&mpshare=1&scene=23&srcid=0115mGMZcZjWkjYGSq6wem4g&sharer_sharetime=1642235406934&sharer_shareid=4ed060cc4cd1efce40e3ab6dd8d8c7d4#rd