psql文档说：
- -v assignment
- --set=assignment
- --variable=assignment
- Perform a variable assignment,like the \set internal command. Note that
- you must separate name and value,if any,by an equal sign on the command line....
但是随着时区的不同，也许是因为这样做：
- These assignments are done during a very early stage of start-up,so variables reserved for internal purposes might get overwritten later.
所以，您似乎必须使用ps命令中的SET命令，或者设置PGTZ环境变量：
- PGTZ=PST8PDT psql -c 'show timezone'
当然，如果您可以全局为用户设置时区(不仅仅是针对这个单独的psql实例)，那么您可以将该变量设置为.bashrc文件(如果在Linux中)
