time — time a command
When a specified
prints the elapsed time during the command or utility,
the time spent in the system,
and the time spent executing the command or utility.
Times are reported in seconds.
Execution time can depend on the performance of the memory
in which the program is running.
The times are printed to standard error.
Note that the shell also has a keyword
that times an entire pipeline if used anywhere in the pipeline.
This action is different than the
command which times a particular command if used in a pipeline.
recognizes the following options:
The command to be executed and timed.
Writes the timing statistics to standard error.
The name of a utility to be invoked and timed.
If the utility operand names any of the shell special built-in utilities,
the time results are undefined.
for information about special built-in utilities.
Any string that is an argument to the
time: SVID2, XPG2, XPG3, XPG4, POSIX.2