Shell执行:时间与/usr/bin/time [英] Shell execution: time vs. /usr/bin/time

问题描述

bash/zsh执行以下操作时会发生什么:

What is going on when bash/zsh does the following:

~ » /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

为什么它会改变我的时间使用方式，为什么zsh会尝试执行-l?

Why does it make a difference how I use time, and why is zsh trying to execute -l??

奇怪的是，zsh说

~ » which time                                                                                                                            
time: shell reserved word

bash却没有:

~ » 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

推荐答案

time内置在zsh和bash中.但是，which仅内置于zsh.在bash中，当您使用which时，它将运行/usr/bin/which，而对外壳程序内置组件一无所知.

time is builtin in both zsh and bash. However, which is only built-in to zsh. In bash, when you use which it runs /usr/bin/which which has no idea about shell built-ins.

因此在bash中，您应该使用:

So in bash, you should use:

$ type time
time is a shell keyword

time -l ...不起作用的原因是time语法不包含-l标志.

The reason time -l ... doesn't work is that the time syntax doesn't include the -l flag.

在两种情况下，都说time是内置函数并不正确.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.它不能实现为功能或外部命令.从这个意义上讲，它类似于if和while之类的其他语法元素.

In both cases, it's not really correct to say that time is 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 if and while.

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