:(){ :|:& };:
A shell function is an object that is called like a simple command and executes a compound command with a
new set of positional parameters.  Shell functions are declared as follows:

name () compound-command [redirection]
function name [()] compound-command [redirection]
       This  defines  a  function  named  name.  The reserved word function is optional.  If the function
       reserved word is supplied, the parentheses are optional.  The body of the function is the compound
       command  compound-command  (see  Compound  Commands  above).   That  command  is usually a list of
       commands between {  and  },  but  may  be  any  command  listed  under  Compound  Commands  above.
       compound-command  is  executed  whenever  name  is specified as the name of a simple command.  Any
       redirections (see REDIRECTION below) specified when a function is defined are performed  when  the
       function  is  executed.   The  exit  status of a function definition is zero unless a syntax error
       occurs or a readonly function with the same name already exists.  When executed, the  exit  status
       of a function is the exit status of the last command executed in the body.  (See FUNCTIONS below.)
call shell function ':'
    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).
If a command is terminated by the control operator &, the shell executes the command in the background in
a subshell.  The shell does not wait for the command to finish, and the return  status  is  0.
Commands separated  by  a ; are executed sequentially; the shell waits for each command to terminate in turn.  The
return status is the exit status of the last command executed.