Linux命令运行时间测试

其实在工作中，还有很多情况下需要测试一个脚本或者程序运行多少时间，特别是对于时间性要求比较高的系统更是如此。对于时间的测试，我们可以用到一个命令：time 。下面我们就详细看看如何使用 time 命令来对脚本/命令进行测时。

time 命令最基本的用法，就是 time + 命令 ，比如：

$ time ping baidu.com 
PING baidu.com (123.125.114.144) 56(84) bytes of data. 
64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=1 ttl=56 time=2.83 ms 
64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=2 ttl=56 time=2.77 ms 
………… 
^C 
--- baidu.com ping statistics --- 
8 packets transmitted, 8 received, 0% packet loss, time 10818ms 
rtt min/avg/max/mdev = 2.765/2.808/2.862/0.039 ms 
 
real    0m11.173s 
user    0m0.004s 
sys     0m0.002s 

在结果里，real 表示从我们执行 ping 命令到最终按 ctrl+c 终止这段时间所耗费的时间;user 及 sys 分别表示 ping 命令在用户空间及内核空间所运行的时间。

如果我们想把时间信息直接写入到文件，而不是显示在屏幕上，那么我们可以使用 -o 选项，并指定写入的文件路径。

$ /usr/bin/time -o /home/alvin/time-output.txt ping baidu.com

执行这个命令后，ping 命令的输出结果依然会在终端里，而 time 命令的结果就写入到我们所指定的 time-output.txt 文件里。

-o 选项表示输出文件不存在就创建，如果存在的话就直接覆盖重写。如果我们不想覆盖重写，而是想追加在文件后面，我们可以使用 -a 选项。

$ /usr/bin/time -a /home/smart/time-output.txt ping linoxide.com

time 命令不带选项的话，显示的信息量比较少，如果我们想获得更详细的信息，那么我们可以使用 -v 选项。

$ /usr/bin/time -v ping baidu.com 
PING baidu.com (123.125.114.144) 56(84) bytes of data. 
64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=1 ttl=56 time=2.75 ms 
64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=2 ttl=56 time=2.76 ms 
64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=3 ttl=56 time=2.85 ms 
64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=4 ttl=56 time=2.77 ms 
^C 
--- baidu.com ping statistics --- 
4 packets transmitted, 4 received, 0% packet loss, time 3300ms 
rtt min/avg/max/mdev = 2.751/2.785/2.851/0.075 ms 
        Command being timed: "ping baidu.com" 
        User time (seconds): 0.00 
        System time (seconds): 0.00 
        Percent of CPU this job got: 0% 
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.64 
        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): 2140 
        Average resident set size (kbytes): 0 
        Major (requiring I/O) page faults: 0 
        Minor (reclaiming a frame) page faults: 626 
        Voluntary context switches: 10 
        Involuntary context switches: 0 
        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 

这个结果信息就相当详细了，我们可以获取到足够多我们所需要的信息。

默认情况下，time 命令只输出 real，usr，sys 三个内容，如果我们想要个性化一些，算定义它的输出格式，time 命令也是支持的。time 命令支持的格式有很多，如下所示：

C - Name and command line arguments used 
D - Average size of the process's unshared data area in kilobytes 
E - Elapsed time in a clock format 
F - Number of page faults 
I - Number of file system inputs by the process 
K - Average total memory use of the process in kilobytes 
M - Maximum resident set the size of the process during the lifetime in Kilobytes 
O - Number of file system outputs by the process 
P - Percentage of CPU that the job received 
R - Number of minor or recoverable page faults 
S - Total number of CPU seconds used by the system in kernel mode 
U - Total number of CPU seconds used by user mode 
W - Number of times the process was swapped out of main memory 
X - Average amount of shared text in the process 
Z - System's page size in kilobytes 
c - Number of times the process was context-switched 
e - Elapsed real time used by the process in seconds 
k - Number of signals delivered to the process 
p - Average unshared stack size of the process in kilobytes 
r - Number of socket messages received by the process 
s - Number of socket messages sent by the process 
t - Average resident set size of the process in kilobytes 
w - Number of time the process was context-switched voluntarily 
x - Exit status of the command 

如果我们想要输出以下这样的格式：

Elapsed Time = 0:01:00, Inputs 2, Outputs 1

我们可以这样自定义：

$ /usr/bin/time -f "Elapsed Time = %E, Inputs %I, Outputs %O" ping baidu.com 
PING baidu.com (220.181.38.148) 56(84) bytes of data. 
64 bytes from 220.181.38.148 (220.181.38.148): icmp_seq=1 ttl=54 time=1.82 ms 
64 bytes from 220.181.38.148 (220.181.38.148): icmp_seq=2 ttl=54 time=1.86 ms 
^C 
--- baidu.com ping statistics --- 
4 packets transmitted, 4 received, 0% packet loss, time 3003ms 
rtt min/avg/max/mdev = 1.825/1.859/1.879/0.056 ms 
Elapsed Time = 0:03.92, Inputs 0, Outputs 0

如果你想让输出的结果有换行，可以在对应的地方添加 /n ，比如：

$ /usr/bin/time -f "Elapsed Time = %E /n Inputs %I /n Outputs %O" ping baidu.com

这样输出的结果就类似于这样：

Elapsed Time = 0:03.92 
Inputs 0 
Outputs 0