time is a bash reserved word to print the time statistics (elapsed (wall-clock) time and user and system time. The use of time as a reserved word permits the timing of:
An external time command cannot time these easily.
The value of the TIMEFORMAT shell variable is used as a format string specifying how the timing information for pipelines should be displayed.
The % character introduces an escape sequence that is expanded to a time value or other information. The escape sequences and their meanings are as follows; the braces denote optional portions.
where:
A trailing newline is added when the format string is displayed.