Date, sleep, and usleep commands, datesleepusleep
1.1 date command
Date is used to obtain and set the Operating System Time, And hwclock is used to obtain the hardware time.
Date has an option "-d", which can be used to describe when to obtain the time. The description method is very open, but the keyword "now" cannot be used, others include 3 days ago, 3 days ago, 3 days ago, yesterday, And next Monday.
Set the display format of the date command in Linux: date [+ format], where"+"Obtains the format from the previous time.For example, date-d "yesterday" + "% Y" obtains the year of yesterday.
The format is as follows.
|
Symbol |
Meaning |
Description |
Year |
% Y |
Year (last two) |
Last two digits of year (00 .. 99) |
% Y |
Year |
Year |
Month |
% M |
Month |
Month (01 .. 12) |
Day |
% J |
Zhongtian |
Day of year (001. 366) |
% D |
Yuzhong |
Day of month (for example, 01) |
% W |
Zhou Zhongtian |
Day of week (0 .. 6); 0 is Sunday |
% U |
Zhou Zhongtian |
Day of week (1 .. 7); 1 is Monday |
Week |
% U |
Mid-week (00-53) |
Week number of year with Sunday as first day |
% W |
Mid-week (00-53) |
Week number of year with Monday as first day |
Hour |
% H |
Hour (24 hour) |
Hour (00 .. 23) |
% I |
Hour (12 hour) |
Hour (01 .. 12) |
Minute |
% M |
Minute |
Minute (00 .. 59) |
Seconds |
% S |
Seconds |
Second (00 .. 60) |
% N |
Nanoseconds |
Ns of current minute |
% S |
Seconds |
Total number of seconds from to the current time |
Complete Format |
% T |
Full time |
Time; same as % H: % M: % S |
% D |
Complete Date Format |
Date; same as % m/% d/% y |
% F |
Complete Date Format |
Date; same as % Y-% m-% d |
Special Format |
% N |
Line feed |
A newline |
% T |
Tab key |
A tab |
[Root @ xuexi ~] # Date + % F2016-09-25 [root @ xuexi ~] # Date + "% F % T" # Use double quotation marks or quotation marks to separate spaces on 10:48:34 [root @ xuexi ~] # Date + "% Y-% m-% d % H: % M: % S" 10:47:49
The date command can be used to calculate the latency (time difference between two time points ). If you want to calculate latency in seconds, you can use % s. However, if you want to calculate latency in milliseconds, microseconds, or even nanoseconds, the date result must be calculated and converted. The following is the second-level time difference calculation method. For details about the second-level time difference calculation method, see: millisecond-level time difference calculation and microsecond-level time difference calculation.
#!/bin/bashstart_time=$(date +"%s")find / -type f -name "*.db" &>/dev/nullend_time=$(date +"%s")time_diff=$(( start_time - end_time ))echo $time_diff
1.2 sleep and usleep
In shell, the sleep command is often used to specify the sleep time. sleep means that the current process enters sleep state. For example:
sleep 5
Sleep is measured in seconds by default. Therefore, sleep is used for 5 seconds. To sleep in milliseconds or microseconds, you can use decimal places. For example:
sleep 0.5
Sleep for half a second.
In addition, there is a dedicated microsecond-level sleep command usleep. For example:
usleep 1000
Sleep is 1000 microseconds, that is, 1 ms.
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