68.shell Script Introduction, shell script structure and execution, date command usage, variables in shell scripts

First, what is the shell?

• The shell is a scripting language aming_linux blog.lishiming.net
• You can use logical judgments, loops, and other syntax
• Functions can be custom-defined
• The shell is a collection of system commands
• Shell scripts can be automated operations, can greatly increase our operational efficiency two, shell script structure and execution methods
• Need to add #!/bin/bash at the beginning
• Lines that begin with # are interpreted as explanatory notes
• The name of the script ends with. SH and is used to differentiate between this is a shell script
• There are two methods of executing
• chmod +x 1.sh;./1.sh
• Bash 1.sh
• View the script execution process bash-x 1.sh
• View script syntax error bash-n 1.sh Third, usage of the date command

    date +%y Four-digit year date +%y two-digit year date +%m                 Month date +%m minute date +%d           05/30/18 format Displays the current day date +%d date (number of days) dates +%y-%m-%d Month date date +%y-%m-%d month Date +%h:%m:%s               Time Division seconds Date +%t time +%s date??          Timestamp date-d @1504620492date-d "+1day" one day after date-d "-1 day" date-d "-1 month ago date-d"-1 min "                 A minute ago date-d "+1hour" an hour later date-d "+1year" a year later date +%w week several date +%w Weeks of the week Cal display Calendar  

%H hours, 24-hour (00~23)
%I Hours, 12-hour (01~12)
%k hours, 24-hour (0~23)
%l hours, 12-hour (1~12)
%M min (00~59)
%p Show AM or PM
%r display time, 12-hour system (HH:MM:SS%p)
%s from January 1, 1970 00:00:00 to the number of seconds currently experienced
%s Display seconds (00~59)
%T display time, 24-hour system (HH:MM:SS)
%x shows the format of Time (%h:%m:%s)
%Z Display time zone, date field (CST)
%a week abbreviation (SUN~SAT)
Full name of%A week (Sunday~saturday)
%h,%b month abbreviation (JAN~DEC)
Full name of%B month (January~december)
%c Date and time (Tue Nov 20 14:12:58 2012)
%d the day of the one month (01~31)
%x,%d Date (MM/DD/YY)
%j the first day of the Year (001~366)
%m Month (01~12)
%w Day of the week one (0 for Sunday)
%W Week of the year (00~53, Monday for first day)
The last two digits of the%y year (1999 is 99)

Iv. variables in shell scripts

• You should use a variable instead when you use a string more frequently in your script and the string length is long
• When using conditional statements, variables are often used?? If [$a-gt 1]; Then ...; Fi
• When referencing the result of a command, replace it with a variable?? n=wc -l 1.txt
• When writing scripts for user interaction, variables are also necessary?? Read-p "Input a number:" N; echo $n?? If you don't write this n, you can use $reply directly.
• Built-in variables, $ $, $ ...? ? $ A represents the script itself, the first parameter, the second ...? ?? ? $ #表示参数个数
• Mathematical Operation a=1;b=2; c=$ (($a + $b)) or $[$a + $b]

68.shell Script Introduction, shell script structure and execution, date command usage, variables in shell scripts