bash Shell 执行：时间 vs. /usr/bin/time
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/19236448/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Shell execution: time vs. /usr/bin/time
提问by emish
What is going on when bash/zsh does the following:
当 bash/zsh 执行以下操作时发生了什么：
~ ? /usr/bin/time -l sleep 1
1.00 real 0.00 user 0.00 sys
516096 maximum resident set size
0 average shared memory size
0 average unshared data size
0 average unshared stack size
145 page reclaims
0 page faults
0 swaps
0 block input operations
0 block output operations
0 messages sent
0 messages received
0 signals received
0 voluntary context switches
2 involuntary context switches
------------------------------------------------------------
~ ? time -l sleep 1
zsh: command not found: -l
-l sleep 1 0.00s user 0.00s system 52% cpu 0.001 total
------------------------------------------------------------
~ ? /usr/bin/time foo
foo: No such file or directory
0.00 real 0.00 user 0.00 sys
------------------------------------------------------------
~ ? time foo
zsh: command not found: foo
foo 0.00s user 0.00s system 52% cpu 0.001 total
Why does it make a difference how I use time, and why is zsh trying to execute -l??
为什么我如何使用时间会有所不同，为什么 zsh 试图执行-l？
Curiously, zsh says
奇怪的是，zsh 说
~ ? which time
time: shell reserved word
While bash doesn't:
虽然 bash 没有：
~ ? bash
bash-3.2$ which time
/usr/bin/time
bash-3.2$ time foo
bash: foo: command not found
real 0m0.006s
user 0m0.000s
sys 0m0.003s
bash-3.2$ /usr/bin/time foo
foo: No such file or directory
0.00 real 0.00 user 0.00 sys
bash-3.2$ time -l sleep 1
bash: -l: command not found
real 0m0.001s
user 0m0.000s
sys 0m0.001s
bash-3.2$ /usr/bin/time -l sleep 1
1.00 real 0.00 user 0.00 sys
516096 maximum resident set size
0 average shared memory size
0 average unshared data size
0 average unshared stack size
144 page reclaims
0 page faults
0 swaps
0 block input operations
1 block output operations
0 messages sent
0 messages received
0 signals received
2 voluntary context switches
2 involuntary context switches
采纳答案by rici
timeis builtin in both zsh and bash. However, whichis only built-in to zsh. In bash, when you use whichit runs /usr/bin/whichwhich has no idea about shell built-ins.
time内置于 zsh 和 bash 中。但是，which仅内置于 zsh 中。在 bash 中，当您使用which它时，它运行时/usr/bin/which不知道 shell 内置函数。
So in bash, you should use:
所以在 bash 中，你应该使用：
$ type time
time is a shell keyword
The reason time -l ...doesn't work is that the timesyntax doesn't include the -lflag.
原因time -l ...不起作用是time语法不包含-l标志。
In both cases, it's not really correct to say that timeis a built-in function. Calling it a "reserved word" or "shell keyword" is more accurate, because it applies to an entire pipeline; it cannot be implemented as a function or external command. In that sense, it is similar to other syntactic elements like ifand while.
在这两种情况下，说这time是一个内置函数是不正确的。称其为“保留字”或“shell 关键字”更为准确，因为它适用于整个管道；它不能作为函数或外部命令来实现。从这个意义上说，它类似于其他句法元素，如ifand while。
回答by Alexis Wilke
Another way to know whether a command is a bash builtin command is to use the helpbuiltin command. The side effect is to get the information about said command (and supported command line arguments.)
了解命令是否为 bash 内置命令的另一种方法是使用help内置命令。副作用是获取有关所述命令（以及支持的命令行参数）的信息。
bash$ help time
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
The value of the TIMEFORMAT variable is used as the output format.
Exit Status:
The return status is the return status of PIPELINE.
For non-builtin commands, helpsays it does not know about it.
对于非内置命令，help表示它不知道。
bash$ help ls
bash: help: no help topics match `ls'. Try `help help' or `man -k ls' or `info ls'.
回答by Dean Povey
time is a builtin function in zsh. It is not in bash. If you want to use the /usr/bin/time version you need to supply the full path when using zsh.
time 是 zsh 中的内置函数。它不在 bash 中。如果要使用 /usr/bin/time 版本，则需要在使用 zsh 时提供完整路径。
It is also possible to disable this behavior using the "disable -r" command in zsh.
也可以使用 zsh 中的“disable -r”命令禁用此行为。
