Which to use of ps ef or ps -ef?

I see there is a difference in output between ps ef and ps -ef. What is that difference, are both commands correct or which is preferred?

2 Answers

man ps says:

This version of ps accepts several kinds of options:
1 UNIX options, which may be grouped and must be preceded by a dash.
2 BSD options, which may be grouped and must not be used with a dash.
3 GNU long options, which are preceded by two dashes.

So, ef uses the BSD e and f options, and -ef uses the Unix -e and -f options. These are different (sections SIMPLE PROCESS SELECTION, OUTPUT FORMAT CONTROL and OUTPUT MODIFIERS respectively):

 -e Select all processes. Identical to -A. -f Do full-format listing. This option can be combined with many other UNIX-style options to add additional columns. It also causes the command arguments to be printed. When used with -L, the NLWP (number of threads) and LWP (thread ID) columns will be added. See the c option, the format keyword args, and the format keyword comm. e Show the environment after the command. f ASCII art process hierarchy (forest).

Clearly, you're not selecting all processes using the ef options, but are using the default listing of processes, plus some additional formatting:

By default, ps selects all processes with the same effective user ID
(euid=EUID) as the current user and associated with the same terminal
as the invoker. It displays the process ID (pid=PID), the terminal
associated with the process (tname=TTY), the cumulated CPU time in
[DD-]hh:mm:ss format (time=TIME), and the executable name (ucmd=CMD).
Output is unsorted by default.
The use of BSD-style options will add process state (stat=STAT) to
the default display and show the command args (args=COMMAND) instead
of the executable name. You can override this with the PS_FORMAT
environment variable. The use of BSD-style options will also change
the process selection to include processes on other terminals (TTYs)
that are owned by you; alternately, this may be described as setting
the selection to be the set of all processes filtered to exclude
processes owned by other users or not on a terminal.

Which should you use? What do you want to do with the output?

Also, see the EXAMPLES section (which does list -ef rather prominently, and doesn't use the BSD e option at all):

EXAMPLES To see every process on the system using standard syntax: ps -e ps -ef ps -eF ps -ely To see every process on the system using BSD syntax: ps ax ps axu To print a process tree: ps -ejH ps axjf

See man ps (the one on your system, on-line can have different explanations).

This version of ps accepts several kinds of options: 1 UNIX options, which may be grouped and must be preceded by a dash. 2 BSD options, which may be grouped and must not be used with a dash. 3 GNU long options, which are preceded by two dashes.

So the 1st method (ps ef) is BSD style and the manual page goes on with

The use of BSD-style options will add process state (stat=STAT) to the default display and show the command args (args=COMMAND) instead of the executable name. You can override this with the PS_FORMAT environment variable. The use of BSD-style options will also change the process selection to include processes on other terminals (TTYs) that are owned by you; alternately, this may be described as setting the selection to be the set of all processes filtered to exclude processes owned by other users or not on a terminal. These effects are not considered when options are described as being "identical" below, so -M will be considered identical to Z and so on.

So both are valid commands but they are not showing the same information.