使用内置的time关键字:

$ help time

time: time [-p] PIPELINE
    Execute PIPELINE and print a summary of the real time, user CPU time,
    and system CPU time spent executing PIPELINE when it terminates.
    The return status is the return status of PIPELINE.  The `-p' option
    prints the timing summary in a slightly different format.  This uses
    the value of the TIMEFORMAT variable as the output format.

例子:

$ time sleep 2

real    0m2.009s
user    0m0.000s
sys     0m0.004s

使用内置的time关键字:

$ help time

time: time [-p] PIPELINE
    Execute PIPELINE and print a summary of the real time, user CPU time,
    and system CPU time spent executing PIPELINE when it terminates.
    The return status is the return status of PIPELINE.  The `-p' option
    prints the timing summary in a slightly different format.  This uses
    the value of the TIMEFORMAT variable as the output format.

例子:

$ time sleep 2

real    0m2.009s
user    0m0.000s
sys     0m0.004s

您可以获得比bash内置时间(即time(1)， Robert Gamble提到过)更详细的信息。通常这是/usr/bin/时间

编者按: 为了确保您调用的是外部实用程序time而不是shell的time关键字，请以/usr/bin/time来调用它 time是posix强制的实用程序，但它需要支持的唯一选项是-p。 特定的平台实现特定的、非标准的扩展:-v与GNU的time实用程序一起工作，如下所示(问题被标记为linux);BSD/macOS实现使用-l来产生类似的输出-参见man 1次。

详细输出示例:

$ /usr/bin/time -v sleep 1
       Command being timed: "sleep 1"
       User time (seconds): 0.00
       System time (seconds): 0.00
       Percent of CPU this job got: 1%
       Elapsed (wall clock) time (h:mm:ss or m:ss): 0:01.05
       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): 0
       Average resident set size (kbytes): 0
       Major (requiring I/O) page faults: 0
       Minor (reclaiming a frame) page faults: 210
       Voluntary context switches: 2
       Involuntary context switches: 1
       Swaps: 0
       File system inputs: 0
       File system outputs: 0
       Socket messages sent: 0
       Socket messages received: 0
       Signals delivered: 0
       Page size (bytes): 4096
       Exit status: 0

如果您只需要精确到秒，您可以使用内置的$SECONDS变量，该变量计算shell已经运行的秒数。

while true; do
    start=$SECONDS
    some_long_running_command
    duration=$(( SECONDS - start ))
    echo "This run took $duration seconds"
    if some_condition; then break; fi
done

如果您想要更精确，请使用%N和date(并使用bc作为diff，因为$(())只处理整数)。

以下是如何做到这一点:

start=$(date +%s.%N)
# do some stuff here
dur=$(echo "$(date +%s.%N) - $start" | bc)

printf "Execution time: %.6f seconds" $dur

例子:

start=$(date +%s.%N); \
  sleep 0.1s; \
  dur=$(echo "$(date +%s.%N) - $start" | bc); \
  printf "Execution time: %.6f seconds\n" $dur

结果:

Execution time: 0.104623 seconds

如果您打算以后使用时间来计算，请学习如何使用/usr/bin/time的-f选项来输出节省时间的代码。下面是我最近使用的一些代码，用于获取和排序整个班级的学生程序的执行时间:

fmt="run { date = '$(date)', user = '$who', test = '$test', host = '$(hostname)', times = { user = %U, system = %S, elapsed = %e } }"
/usr/bin/time -f "$fmt" -o $timefile command args...

后来我将所有$timefile文件连接起来，并将输出输出到Lua解释器中。你可以用Python或bash或任何你喜欢的语法做同样的事情。我喜欢这个技巧。