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(bashref.info)Pipelines

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Pipelines
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   A `pipeline' is a sequence of simple commands separated by `|'.

   The format for a pipeline is
     [`time' [`-p']] [`!'] COMMAND1 [`|' COMMAND2 ...]

The output of each command in the pipeline is connected via a pipe to
the input of the next command.  That is, each command reads the
previous command's output.

   The reserved word `time' causes timing statistics to be printed for
the pipeline once it finishes.  The statistics currently consist of
elapsed (wall-clock) time and user and system time consumed by the
command's execution.  The `-p' option changes the output format to that
specified by POSIX.  The `TIMEFORMAT' variable may be set to a format
string that specifies how the timing information should be displayed.
Note: Bash Variables, for a description of the available formats.
The use of `time' as a reserved word permits the timing of shell
builtins, shell functions, and pipelines.  An external `time' command
cannot time these easily.

   If the pipeline is not executed asynchronously (Note: Lists), the
shell waits for all commands in the pipeline to complete.

   Each command in a pipeline is executed in its own subshell (Note:
Command Execution Environment).  The exit status of a pipeline is the
exit status of the last command in the pipeline.  If the reserved word
`!' precedes the pipeline, the exit status is the logical negation of
the exit status of the last command.