The difference in the output format of the time command in your examples is due to how time is being invoked and which version of time is being used in each case.

1. time echo -n

In this case, time is a shell builtin (likely from bash). The output format is:

text
Copy
real    0m0.000s
user    0m0.000s
sys     0m0.000s

This is the default format for the bash builtin time command.

2. echo | time echo -n

Here, time is not a shell builtin but the external /usr/bin/time command. The output format is more detailed:

text
Copy
0.00user 0.00system 0:00.00elapsed 100%CPU (0avgtext+0avgdata 1804maxresident)k
0inputs+0outputs (0major+99minor)pagefaults 0swaps

This is the output of the GNU time command (/usr/bin/time), which provides additional metrics like memory usage, I/O, and page faults.

Why the Difference?

• Shell Builtin vs. External Command:

  • When you run time echo -n, bash uses its builtin time command.
  • When you run echo | time echo -n, the shell interprets time as the external /usr/bin/time command because the pipe (|) forces the shell to look for an external executable.

• Different Implementations:

  • The bash builtin time is simpler and only reports real, user, and sys times.
  • The external /usr/bin/time (GNU time) provides a more detailed breakdown of resource usage.

How to Force the Same Behavior

If you want to use the external /usr/bin/time explicitly, you can call it directly:

bash
Copy
/usr/bin/time echo -n

This will give you the detailed output even without a pipe.

Alternatively, if you want to use the bash builtin time in the second case, you can use:

bash
Copy
echo | bash -c "time echo -n"

Summary Table