[postgres@rhel73 data]$ psql -l       ------->>>查询默认cluster下的所有数据库,并退出
                                  List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges   
-----------+----------+----------+-------------+-------------+-----------------------
 postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | 
 template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
 test      | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | 
(4 rows)

[postgres@rhel73 data]$ psql -xl     ------->>>以扩展的形式查询cluster下的所有数据库,并退出
List of databases
-[ RECORD 1 ]-----+----------------------
Name              | postgres
Owner             | postgres
Encoding          | UTF8
Collate           | en_US.UTF-8
Ctype             | en_US.UTF-8
Access privileges | 
-[ RECORD 2 ]-----+----------------------
Name              | template0
Owner             | postgres
Encoding          | UTF8
Collate           | en_US.UTF-8
Ctype             | en_US.UTF-8
Access privileges | =c/postgres          +
                  | postgres=CTc/postgres
-[ RECORD 3 ]-----+----------------------
Name              | template1
Owner             | postgres
Encoding          | UTF8
Collate           | en_US.UTF-8
Ctype             | en_US.UTF-8
Access privileges | =c/postgres          +
                  | postgres=CTc/postgres
-[ RECORD 4 ]-----+----------------------
Name              | test
Owner             | postgres
Encoding          | UTF8
Collate           | en_US.UTF-8
Ctype             | en_US.UTF-8
Access privileges | 

[postgres@rhel73 data]$ psql --help ------------>>>>psql的帮助命令.
psql is the Postgresql interactive terminal.


Usage:
  psql [OPTION]... [DBNAME [USERNAME]]


General options:
  -c,--command=COMMAND    run only single command (sql or internal) and exit
  -d,--dbname=DBNAME      database name to connect to (default: "postgres")
  -f,--file=FILENAME      execute commands from file,then exit
  -l,--list               list available databases,then exit
  -v,--set=,--variable=NAME=VALUE
                           set psql variable NAME to VALUE
                           (e.g.,-v ON_ERROR_STOP=1)
  -V,--version            output version information,then exit
  -X,--no-psqlrc          do not read startup file (~/.psqlrc)
  -1 ("one"),--single-transaction
                           execute as a single transaction (if non-interactive)
  -?,--help[=options]     show this help,then exit
      --help=commands      list backslash commands,then exit
      --help=variables     list special variables,then exit


Input and output options:
  -a,--echo-all           echo all input from script
  -b,--echo-errors        echo Failed commands
  -e,--echo-queries       echo commands sent to server
  -E,--echo-hidden        display queries that internal commands generate
  -L,--log-file=FILENAME  send session log to file
  -n,--no-readline        disable enhanced command line editing (readline)
  -o,--output=FILENAME    send query results to file (or |pipe)
  -q,--quiet              run quietly (no messages,only query output)
  -s,--single-step        single-step mode (confirm each query)
  -S,--single-line        single-line mode (end of line terminates sql command)


Output format options:
  -A,--no-align           unaligned table output mode
  -F,--field-separator=STRING
                           field separator for unaligned output (default: "|")
  -H,--html               HTML table output mode
  -P,--pset=VAR[=ARG]     set printing option VAR to ARG (see \pset command)
  -R,--record-separator=STRING
                           record separator for unaligned output (default: newline)
  -t,--tuples-only        print rows only
  -T,--table-attr=TEXT    set HTML table tag attributes (e.g.,width,border)
  -x,--expanded           turn on expanded table output
  -z,--field-separator-zero
                           set field separator for unaligned output to zero byte
  -0,--record-separator-zero
                           set record separator for unaligned output to zero byte


Connection options:
  -h,--host=HOSTNAME      database server host or socket directory (default: "local socket")
  -p,--port=PORT          database server port (default: "5432")
  -U,--username=USERNAME  database user name (default: "postgres")
  -w,--no-password        never prompt for password
  -W,--password           force password prompt (should happen automatically)


For more information,type "\?" (for internal commands) or "\help" (for sql
commands) from within psql,or consult the psql section in the Postgresql
documentation.

Report bugs to <pgsql-bugs@postgresql.org>.
[postgres@rhel73 data]$ psql -V    -------------->>>查看psql版本的命令.
psql (Postgresql) 9.6.0
[postgres@rhel73 data]$