Question

当bash / zsh执行以下操作时会发生什么：

~ » /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

为什么我的使用时间有所不同，为什么zsh试图执行-l ??

奇怪的是，zsh说

~ » which time                                                                                                                            
time: shell reserved word

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

Answer 1

time内置于zsh和bash中。但是，which仅内置于zsh。在bash中，当你使用which时，它运行/usr/bin/which，它不知道shell内置函数。

所以在bash中，你应该使用：

$ type time
time is a shell keyword

time -l ...不起作用的原因是time语法不包含-l标记。

在这两种情况下，说time是内置函数并不正确。将其称为“保留字”或“shell关键字”更准确，因为它适用于整个管道;它不能作为函数或外部命令实现。从这个意义上说，它类似于if和while等其他句法元素。

Answer 2

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的信息（以及支持的命令行参数。）

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.

对于非内置命令，help表示它不知道它。

bash$ help ls
bash: help: no help topics match `ls'.  Try `help help' or `man -k ls' or `info ls'.

Answer 3

时间是zsh中的内置函数。它不是在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。

也可以使用zsh中的“disable -r”命令禁用此行为。

Shell执行：时间与/ usr / bin /时间

3 个答案: