外部命令“时间”和保留字“时间”时间可以是什么？

我的答案是关于Linux的。

1. 哪个规则阻止它计时其他内容？

我猜它只获取进程的时间信息，因为它实际上使用wait4系统调用来获取此时间信息。的第一个参数wait4是进程的pid。因此，请/usr/bin/time务必先致电execve，然后再等待4。

顺便一提：

execve（）执行文件名指向的程序。filename必须是二进制可执行文件，或者是以以下形式的行开头的脚本：＃！解释器[optional-arg]

所以/ usr / bin / time需要一些可以由 execve

2. Bash的保留字时间可以计时所有可以运行的内容吗？

我猜是。它被实现为两组呼叫：

10:06:03 getrusage(RUSAGE_SELF, {ru_utime={0, 152976}, ru_stime={0, 465929}, ru_maxrss=4052, ru_ixrss=0, ru_idrss=0, ru_isrss=0, ru_minflt=6214, ru_majflt=1, ru_nswap=0, ru_inblock=368, ru_oublock=0, ru_msgsnd=0, ru_msgrcv=0, ru_nsignals=0, ru_nvcsw=6349, ru_nivcsw=12}) = 0
10:06:03 getrusage(RUSAGE_CHILDREN, {ru_utime={2, 259656}, ru_stime={1, 888712}, ru_maxrss=21176, ru_ixrss=0, ru_idrss=0, ru_isrss=0, ru_minflt=64297, ru_majflt=4, ru_nswap=0, ru_inblock=272, ru_oublock=368, ru_msgsnd=0, ru_msgrcv=0, ru_nsignals=0, ru_nvcsw=56077, ru_nivcsw=386}) = 0

运行命令或内置

10:06:04 getrusage(RUSAGE_SELF, {ru_utime={0, 152976}, ru_stime={0, 476927}, ru_maxrss=4052, ru_ixrss=0, ru_idrss=0, ru_isrss=0, ru_minflt=6243, ru_majflt=1, ru_nswap=0, ru_inblock=368, ru_oublock=0, ru_msgsnd=0, ru_msgrcv=0, ru_nsignals=0, ru_nvcsw=6399, ru_nivcsw=13}) = 0
10:06:04 getrusage(RUSAGE_CHILDREN, {ru_utime={2, 271654}, ru_stime={1, 903710}, ru_maxrss=21176, ru_ixrss=0, ru_idrss=0, ru_isrss=0, ru_minflt=64514, ru_majflt=4, ru_nswap=0, ru_inblock=272, ru_oublock=368, ru_msgsnd=0, ru_msgrcv=0, ru_nsignals=0, ru_nvcsw=56079, ru_nivcsw=406}) = 0

所以我想bash只是计算出一个差异并打印出来。通过这种方式，它可以测量任何东西，例如自己的内置文件或子进程

3. 外部时间可以计时但保留字时间不能计时的是什么？

实际上，这两个系统调用getrusage，并wait4从内核获得结构rusage使用。但是bash time，从此结构中打印有限数量的字段。这是从man 1 time：

注意：某些外壳程序（例如bash（1））具有内置的time命令，该命令提供的功能少于此处描述的命令。

$/usr/bin/time -v  seq 10000
    Command being timed: "seq 10000"
    User time (seconds): 0.01
    System time (seconds): 0.01
    Percent of CPU this job got: 24%
    Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.12
    Average shared text size (kbytes): 0
    Average unshared data size (kbytes): 0
    Average stack size (kbytes): 0
    Average total size (kbytes): 0
    Maximum resident set size (kbytes): 2640
    Average resident set size (kbytes): 0
    Major (requiring I/O) page faults: 0
    Minor (reclaiming a frame) page faults: 199
    Voluntary context switches: 8
    Involuntary context switches: 24
    Swaps: 0
    File system inputs: 0
    File system outputs: 8
    Socket messages sent: 0
    Socket messages received: 0
    Signals delivered: 0
    Page size (bytes): 4096
    Exit status: 0