Gnu time and formatting output

问题

I wanted to use gnu time to measure running time of some little .c programs. In the man it is written that:

-f FORMAT, --format FORMAT
Use FORMAT as the format string that controls the output of time.  See the below more information.

Then in examples we have:

To run the command `ls -Fs' and show just the user, system, and total time:
time -f "%E real,%U user,%S sys" ls -Fs

But when I try to issue this command from example i get:

time -f '%E real,%U user,%S sys' ls -Fs
-f: command not found

real    0m0.134s
user    0m0.084s
sys     0m0.044s

I am wondering where is the problem, where am I making a mistake? I just want to show the user time, that is why I am toying with time output format.

回答1:

Bash for one has a shell builtin named time. One way to get past it is to type command time - command will ignore the builtins and run the time program from your $PATH. Another way is alias time=/usr/bin/time. On the other hand the bash builtin respects environment variable TIMEFORMAT.

来源：https://stackoverflow.com/questions/9715570/gnu-time-and-formatting-output