x Lift the BSD-style "must have a tty" restriction, which is imposed upon the set of all
processes when some BSD-style (without "-") options are used or when the ps personality
setting is BSD-like. The set of processes selected in this manner is in addition to the
set of processes selected by other means. An alternate description is that this option
causes ps to list all processes owned by you (same EUID as ps), or to list all processes
when used together with the a option.
o format Specify user-defined format. Identical to -o and --format.
-o format User-defined format.
format is a single argument in the form of a blank-separated or comma-separated list,
which offers a way to specify individual output columns. The recognized keywords are
described in the STANDARD FORMAT SPECIFIERS section below. Headers may be renamed
(ps -o pid,ruser=RealUser -o comm=Command) as desired. If all column headers are empty
(ps -o pid= -o comm=) then the header line will not be output. Column width will increase
as needed for wide headers; this may be used to widen up columns such as WCHAN
(ps -o pid,wchan=WIDE-WCHAN-COLUMN -o comm). Explicit width control
(ps opid,wchan:42,cmd) is offered too. The behavior of ps -o pid=X,comm=Y varies with
personality; output may be one column named "X,comm=Y" or two columns named "X" and "Y".
Use multiple -o options when in doubt. Use the PS_FORMAT environment variable to specify
a default as desired; DefSysV and DefBSD are macros that may be used to choose the
default UNIX or BSD columns.
A pipeline is a sequence of one or more commands separated by one of the control operators | or |&. The
format for a pipeline is:
[time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]
The standard output of command is connected via a pipe to the standard input of command2. This
connection is performed before any redirections specified by the command (see REDIRECTION below). If |&
is used, the standard error of command is connected to command2's standard input through the pipe; it is
shorthand for 2>&1 |. This implicit redirection of the standard error is performed after any
redirections specified by the command.
The return status of a pipeline is the exit status of the last command, unless the pipefail option is
enabled. If pipefail is enabled, the pipeline's return status is the value of the last (rightmost)
command to exit with a non-zero status, or zero if all commands exit successfully. If the reserved word
! precedes a pipeline, the exit status of that pipeline is the logical negation of the exit status as
described above. The shell waits for all commands in the pipeline to terminate before returning a value.
If the time reserved word precedes a pipeline, the elapsed as well as user and system time consumed by
its execution are reported when the pipeline terminates. The -p option changes the output format to that
specified by POSIX. When the shell is in posix mode, it does not recognize time as a reserved word if
the next token begins with a `-'. The TIMEFORMAT variable may be set to a format string that specifies
how the timing information should be displayed; see the description of TIMEFORMAT under Shell Variables
When the shell is in posix mode, time may be followed by a newline. In this case, the shell displays the
total user and system time consumed by the shell and its children. The TIMEFORMAT variable may be used
to specify the format of the time information.
Each command in a pipeline is executed as a separate process (i.e., in a subshell).