Why doesn't the `time` command work with any option?

Question

I tried to use time command with -f option to format the output of time, but I get the following error:

-f: command not found

Then I tried to use other options -a, -o, etc and I get the same error. Not even time --version doesn't work (--version: command not found).

Don't tell me to read the man because I already do it by many times... All these options are specified there. So, where could be the problem?

Does sudo apt-get install --reinstall time help? – jobin Mar 14 '14 at 17:53 — jobin, Mar 14 '14 at 17:53
Or maybe the internal shell time with /usr/bin/time – Rmano Mar 14 '14 at 17:53 — Rmano, Mar 14 '14 at 17:53

score 130 · Accepted Answer · edited Sep 23 '22 at 12:37

130

Well, even if you don't like it, I will put you to read again with more attention man time. At the end of EXAMPLES section you will find:

  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

So, I'm assuming that you use bash shell which uses an internal version of time, provided as a shell keyword. You can check this using the following command:

type time

and the output will probably be:

time is a shell keyword

If this is the case, then it is clear that to use the real time command you must use its explicit path: /usr/bin/time.

Further, if you don't want to use anymore the shell keyword time, you can create a permanent alias as follow:

alias time='/usr/bin/time'

This will overwrite the shell keyword time because the command:

type time

will give the following output now:

time is aliased to `/usr/bin/time'

edited Sep 23 '22 at 12:37

user7440787

123

answered Mar 14 '14 at 17:56

Radu Rădeanu

169,590

7

for the shell built commands: {info time} and {type time}. For the binary commands: {which time} and {man time} – Michael Martinez Mar 14 '14 at 19:09
1

@Michael info time is about the binary. help time is about the builtin. – wjandrea Dec 23 '18 at 04:26
yep, sorry I was thinking "help" but out came "info" – Michael Martinez Jan 07 '19 at 17:15
1

I skimmed the man page three times and still missed the bash caveat. I guess the adage is RTFM and not SkimTFM for a reason... – SO_fix_the_vote_sorting_bug May 27 '21 at 16:22
3

Rather than write out the full path to the binary, you can escape a command (i.e. \time) to avoid it being interpreted as a shell builtin or alias. – Jivan Pal Jul 27 '21 at 20:46

score 28 · Answer 2 · edited Sep 01 '19 at 04:02

28

Since, as the other answers explain, time is a shell keyword, the only option available to you is -p:

terdon@oregano ~ $ help time
time: time [-p] pipeline
    Report time consumed by pipeline's execution.

Execute PIPELINE and print a summary of the real time, user CPU time,
and system CPU time spent executing PIPELINE when it terminates.

Options:
  -p    print the timing summary in the portable Posix format

So, you need to run the time that's in /usr/bin. Here are a few ways to do so:

Use the time executable instead:
```
/usr/bin/time -f %Uuser ls >/dev/null
```
Use \ which causes your shell to ignore aliases and keywords and instead search your $PATH for a matching executable:
```
\time -f %Uuser ls >/dev/null 
```
Use the command builtin which has a similar effect:
```
command time -f %Uuser ls >/dev/null
```
Use a different shell, one that has no such keyword. For example sh (which is actually dash on Ubuntu):
```
sh -c "time -f %Uuser ls >/dev/null"
```
Use which, which will search through your $PATH (OK, this one is silly):
```
$(which time) -f %Uuser ls >/dev/null
```

edited Sep 01 '19 at 04:02

Eliah Kagan

117,780

answered Mar 14 '14 at 18:10

terdon

100,812

Is there a way to do the opposite - replicate built-in time with regular /usr/bin/time? I.e. to translate bash script into dash. – Dan M. Sep 26 '19 at 12:06
@DanM. I don't understand. If you want the builtin time, run time. If you want the standalone executable, run /usr/bin/time. – terdon Sep 26 '19 at 12:10
there is no built-in time on Ubuntu's default shell as far as I'm aware. I want to translate script using built-in into standalone with the same behavior. – Dan M. Sep 26 '19 at 12:13
@DanM. then just use time. It will call whichever one is available. That will be the builtin for bash and the standalone for dash. If you use /usr/bin/time, then it will always call the standalone, both in bash and in dash. But it sounds like you should probably be asking a new question, explaining the behavior you need. Let me know if you do and I'll try and help. – terdon Sep 26 '19 at 12:18
yeah, but built-in and standalone have drastically different syntax/semantics. Anyway, thanks. I'll ask a new question if I won't figure out how to deal with it myself. – Dan M. Sep 26 '19 at 12:31
@DanM. if you write your script so it always uses /usr/bin/time, then you don't need to worry about if it is being run by dash or bash. – terdon Sep 26 '19 at 12:32

score 17 · Answer 3 · answered Mar 14 '14 at 17:54

17

The bash and zsh shells have their internal time command. You have to use

/usr/bin/time -f ...

BTW, I discovered that using (from zsh):

~% which  time
time: shell reserved word

answered Mar 14 '14 at 17:54

Rmano

31,947

Why doesn't the `time` command work with any option?

3 Answers3

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