time option doesn't work

Question

I tried to measure execution time and format it with this command:

time -f "%e" ./1 1000 1
-f: command not found

real    0m0.066s
user    0m0.044s
sys 0m0.023s

But such command works:

/usr/bin/time -f "%e" ./1 1000 1
31245 212 443
0.00

I tried to determine where another time is located, but all showes to /usr/bin/time

which time
/usr/bin/time

or

whereis time
time: /usr/bin/time /usr/bin/X11/time /usr/include/time.h /usr/share/man/man7/time.7.gz /usr/share/man/man2/time.2.gz /usr/share/man/man1/time.1.gz

or

type -a time
time is a shell keyword
time is /usr/bin/time

How to define where another time is located?

Answer 1

Users of the bash shell need to use an explicit path in order to run the external time command and not the shell builtin variant. On system where time is installed in /usr/bin, the first example would become

   /usr/bin/time wc /etc/hosts

OR

Note: some shells (eg, bash(1)) have a built-in time command that provides less functionality than the command described here. To access the real command, you may need to specify its pathname (something like /usr/bin/time).

http://man7.org/linux/man-pages/man1/time.1.html