When you try to shrink Volume/File system using '-' sign in the command as follows, it results in an error.. 
#/etc/vx/bin/vxresize -g DG Volume_Name -Size E.g. #/etc/vx/bin/vxresize -g testdg testvol -2g #/etc/vx/bin/vxresize -g testdg testvol -2g vxresize: invalid option -- 2 VxVM vxresize INFO V-5-1-10092 usage: vxresize [-hHvMDxsnbf] [-F fstype] [-g diskgroup] [-t tag] [-o verify|override] volume length [media...]  | 
Since '-2g' starts with '-' character, the standard UNIX getopt will treat it as an option. 
Resolution:
In order to tell getopt(3) to terminate the option scanning, you have to specify '--'. 
#/etc/vx/bin/vxresize -g DG Volume_Name -- -Size E.g. #/etc/vx/bin/vxresize -g testdg testvol -- -2g  |