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[fakename]$ help time
time: time [-p] pipeline
    Report time consumed by pipeline's execution...

From this, it seems that time is a Bash builtin. However, I cannot find a description of it on this page: https://www.gnu.org/software/bash/manual/html_node/Shell-Builtin-Commands.html#Shell-Builtin-Commands. Why is this the case?

  • 1
    Use type time to see what it is. – muru Aug 1 '18 at 22:55
  • man bash and then just type /time – George Vasiliou Aug 1 '18 at 23:09
  • and don't forget /usr/bin/time which is similar to bash's time but different.... – ivanivan Aug 2 '18 at 13:20
22

It is described in the "Shell Grammar/Pipelines" subsection of the bash manpage. It is also described in the link that you provided in the Pipelines section, where it is indexed under "Reserved Words".

Pipelines

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 [ | or |& 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. 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 below.

Each command in a pipeline is executed as a separate process (i.e., in a subshell).

5

The Bash Reference Manual may be viewed on the console using info. Then, a user can search a keyword in indexes pressing the key i, typing the keyword and pressing the key Enter. info will jumps to the first location, in the manual, associated to the keyword. Press , to reach other locations. For more information, read the GNU Info manual, online, or on the console using info info. Indeed, the most important thing to quickly find a keyword, in a manual, is to use an existing index.

The essential fact about the issue is that time is not a builtin but a Bash reserved word or keyword.

# See Also

  • Ahhh, thanks. Yes, I am seeing that now with type time. See, this is interesting though. help help yields "Display information about builtin commands," and yet help also has help information for keywords? – extremeaxe5 Aug 2 '18 at 16:31

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