-- TOC --
time命令主要用来观察某个程序的执行时间，使用此命令很简单，理解其输出稍微费点劲。
显示系统时间，使用date命令。
bash builin了一个time命令，一般用这个就可以：
$ time python3 pingscan.py 192.168.16.1/24
Pingscan network 192.168.16.1/24 with 128 workers (mt_ping):
192.168.16.1 4/4
192.168.16.100 4/4
Hosts: 2/254
real 0m5.554s
user 0m0.623s
sys 0m0.731s
网络中只有我的主机和网管。
time命令的输出有3个时间：
在uniprocessor环境下，基本上 real >= user + sys
在multiprocessor环境下就不一定了，当程序可以充分利用多核的时候，很可能得到的结果是 real < user + sys 。
这是另一个time程序，它的输出要稍微复杂一点：
$ \time python3 pingscan.py 192.168.16.1/24
Pingscan network 192.168.16.1/24 with 128 workers (mt_ping):
192.168.16.1 4/4
192.168.16.100 4/4
Hosts: 2/254
0.58user 0.80system 0:05.58elapsed 24%CPU (0avgtext+0avgdata 18288maxresident)k
0inputs+0outputs (0major+153517minor)pagefaults 0swaps
用
\escape的方式，阻止bash调用它内置的time程序。
一般要加上-v参数，结果看起来会方便一些：
$ \time -v python3 pingscan.py 192.222.0.0/20
Pingscan network 192.222.0.0/20 with 128 workers (mt_ping):
192.222.0.12 4/4
192.222.0.11 4/4
192.222.0.15 4/4
192.222.0.16 4/4
192.222.0.10 3/4
192.222.0.18 3/4
192.222.0.19 3/4
192.222.0.21 3/4
192.222.0.211 4/4
192.222.0.213 4/4
192.222.0.212 4/4
192.222.0.219 4/4
192.222.0.254 4/4
192.222.1.6 4/4
192.222.1.7 4/4
192.222.1.8 4/4
192.222.1.9 4/4
192.222.1.13 4/4
192.222.1.17 4/4
192.222.1.19 4/4
192.222.1.20 4/4
192.222.1.30 4/4
192.222.1.26 4/4
192.222.1.31 4/4
192.222.1.32 4/4
192.222.1.34 4/4
192.222.1.35 4/4
192.222.1.36 4/4
192.222.1.39 4/4
192.222.1.42 4/4
192.222.1.60 4/4
192.222.1.57 4/4
192.222.1.78 4/4
192.222.1.145 4/4
192.222.1.149 4/4
192.222.1.150 4/4
192.222.1.151 4/4
192.222.1.155 3/4
192.222.1.157 4/4
192.222.1.158 4/4
192.222.1.159 4/4
192.222.1.160 4/4
192.222.1.190 4/4
192.222.1.207 4/4
192.222.1.254 4/4
192.222.2.8 4/4
192.222.2.9 4/4
192.222.2.6 4/4
192.222.2.7 4/4
192.222.1.253 4/4
192.222.2.17 4/4
192.222.2.19 4/4
192.222.2.31 4/4
192.222.2.35 4/4
192.222.2.39 4/4
192.222.2.30 3/4
192.222.2.34 3/4
192.222.2.36 3/4
192.222.2.42 4/4
192.222.2.57 4/4
192.222.2.60 3/4
192.222.2.78 3/4
192.222.2.151 4/4
192.222.3.6 4/4
192.222.3.7 4/4
192.222.3.9 4/4
192.222.3.8 4/4
192.222.3.17 4/4
192.222.3.19 3/4
192.222.3.30 4/4
192.222.3.31 4/4
192.222.3.35 4/4
192.222.3.34 4/4
192.222.3.36 4/4
192.222.3.39 4/4
192.222.3.42 4/4
192.222.3.57 4/4
192.222.3.60 4/4
192.222.3.78 4/4
192.222.3.151 4/4
192.222.5.1 4/4
192.222.5.2 4/4
192.222.5.5 4/4
192.222.5.8 4/4
192.222.5.7 4/4
192.222.5.9 4/4
192.222.5.13 4/4
192.222.5.12 4/4
192.222.5.14 4/4
192.222.5.20 4/4
192.222.5.19 4/4
192.222.5.22 4/4
192.222.5.21 4/4
192.222.5.23 4/4
192.222.5.24 4/4
192.222.5.28 4/4
192.222.5.32 4/4
192.222.5.16 3/4
192.222.5.64 4/4
192.222.5.73 4/4
192.222.5.69 3/4
192.222.5.81 4/4
192.222.5.83 4/4
192.222.5.84 4/4
192.222.5.99 4/4
192.222.5.100 4/4
192.222.5.110 4/4
192.222.5.116 4/4
192.222.5.118 4/4
192.222.5.143 4/4
192.222.5.146 4/4
192.222.5.147 4/4
192.222.5.148 4/4
192.222.5.174 4/4
192.222.5.176 3/4
192.222.5.177 3/4
192.222.6.18 4/4
192.222.8.14 4/4
192.222.8.13 4/4
192.222.8.15 4/4
192.222.8.22 4/4
192.222.8.23 4/4
192.222.8.41 4/4
192.222.8.42 4/4
192.222.8.46 4/4
192.222.8.61 4/4
192.222.8.62 4/4
192.222.8.65 4/4
192.222.8.66 4/4
192.222.8.88 4/4
192.222.8.89 4/4
192.222.8.90 2/4
192.222.8.106 4/4
192.222.8.107 4/4
192.222.8.108 3/4
192.222.8.120 1/4
192.222.8.128 3/4
192.222.8.36 3/4
192.222.8.140 4/4
192.222.8.147 4/4
192.222.8.171 4/4
192.222.8.149 3/4
192.222.8.170 3/4
192.222.8.201 3/4
192.222.8.231 4/4
192.222.8.232 4/4
192.222.8.251 4/4
192.222.8.254 4/4
192.222.9.2 4/4
192.222.8.175 1/4
192.222.9.24 4/4
192.222.9.35 4/4
192.222.9.63 3/4
192.222.9.69 4/4
192.222.9.75 4/4
192.222.9.86 4/4
192.222.9.89 4/4
192.222.9.99 4/4
192.222.9.105 4/4
192.222.9.87 2/4
192.222.9.116 4/4
192.222.9.121 4/4
192.222.9.119 4/4
192.222.9.126 3/4
192.222.9.142 4/4
192.222.9.151 4/4
192.222.9.36 2/4
192.222.9.153 4/4
192.222.9.167 4/4
192.222.9.168 4/4
192.222.9.169 4/4
192.222.9.170 4/4
192.222.9.186 4/4
192.222.9.161 3/4
192.222.9.162 3/4
192.222.9.166 3/4
192.222.9.212 4/4
192.222.9.231 4/4
192.222.9.232 4/4
192.222.9.236 4/4
192.222.9.247 3/4
192.222.10.3 4/4
192.222.10.11 4/4
192.222.10.12 4/4
192.222.10.17 4/4
192.222.10.8 3/4
192.222.10.25 4/4
192.222.10.14 3/4
192.222.10.31 4/4
192.222.10.27 3/4
192.222.10.49 4/4
192.222.10.58 4/4
192.222.10.60 4/4
192.222.10.61 4/4
192.222.10.70 4/4
192.222.10.75 4/4
192.222.10.79 4/4
192.222.10.85 4/4
192.222.10.88 4/4
192.222.10.62 3/4
192.222.10.73 3/4
192.222.10.92 4/4
192.222.10.102 4/4
192.222.10.103 4/4
192.222.10.119 4/4
192.222.10.124 4/4
192.222.10.128 4/4
192.222.10.134 4/4
192.222.10.139 4/4
192.222.10.127 2/4
192.222.10.130 3/4
192.222.10.142 3/4
192.222.10.152 4/4
192.222.10.181 4/4
192.222.10.176 3/4
192.222.10.178 3/4
192.222.10.200 4/4
192.222.10.209 4/4
192.222.10.210 4/4
192.222.10.227 4/4
192.222.10.212 3/4
192.222.10.240 4/4
192.222.10.238 3/4
192.222.15.2 4/4
192.222.15.3 4/4
192.222.15.4 4/4
192.222.15.5 4/4
192.222.15.6 4/4
192.222.15.14 4/4
192.222.15.16 4/4
192.222.15.17 4/4
192.222.15.18 4/4
192.222.15.22 4/4
192.222.15.190 4/4
192.222.15.224 4/4
Hosts: 235/4094
Command being timed: "python3 pingscan.py 192.222.0.0/20"
User time (seconds): 9.15
System time (seconds): 13.17
Percent of CPU this job got: 27%
Elapsed (wall clock) time (h:mm:ss or m:ss): 1:21.88
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): 23424
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 49
Minor (reclaiming a frame) page faults: 2826958
Voluntary context switches: 89032
Involuntary context switches: 15236
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
/usr/bin/time除了统计时间之外，还能够统计程序时间的内存情况，CPU占用等信息，只是这些统计信息还有些看不懂。
本文链接：https://cs.pynote.net/sf/linux/shell/202201041/
-- EOF --
-- MORE --