67. Shell Script Introduction, shell script structure and execution, date command usage, variables in shell script
First, Shell script introduction
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
Define the purpose of the function: In order to simplify, in order to reduce duplication of code.
The shell is a collection of system commands
Shell scripts enable automated operations, which can greatly increase our operational efficiency
Second, shell script structure and execution
The first need to add #!/bin/bash, the script in the current machine execution can recognize the inside of the command, the other machine may not recognize the execution, so need to add this line. The following command is written by/bin/bash the interpreter to parse the execution, and it is the function of this.
The line starting with # in the second line is the explanatory note
The name of the script ends with. SH and is used to differentiate between this is a shell script
There are two methods of execution:
# mkdir Shell
# CD shell/
# sh 01.sh
# chmod A+x 01.sh
View the script execution process bash-x 1.sh
See if the script is syntactically incorrect, but can't check out the non-existent command bash-n 1.sh
Iii. use of the date command
Date +%y-%m-%d = Date +%f Month Day
Date +%y-%m-%d Month Day
y:2018, Y:18. Year two-bit or four-bit
M: Month, M: minutes. M:05,h:5 Month
D: Sun, D:05/30/18 (May 30, 18)
Date +%h:%m:%s = Date +%t time
S: seconds, S: timestamp, how many seconds elapsed from January 1, 1970 0:0.
Date +%s Timestamp
Cal: Look at the calendar for the entire month.
Date-d @1504620492 @ back with timestamp
Date-d "+1day" a day later
Date-d "-1 days" a day ago
Date-d "-1 month" month ago
Date-d "-1 month" +%f
Date-d "-1 years" a year ago
Date-d "-1 year" +%f
Date-d "-1 min" A minute ago
Date-d "-1 Hour" +%t
Date +%w, date +%w Week
W: Week, Monday Tuesday. W: The first few weeks of the year.
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, the variable if [$a-gt 1] is often used; Then ...; Fi
Replace n= ' Wc-l 1.txt ' with a variable when referencing the result of a command
When writing and user interaction scripts, variables are also essential for read-p "Input a number:" N; Echo $n If you don't write this n, you can use $reply directly.
Built-in variables $, $ $, $ ... $ $ represents the script itself, the first parameter, the $ A second ... $ #表示参数个数
Mathematical Operation a=1;b=2; c=$ (($a + $b)) or $[$a + $b]
67. Shell script Introduction, shell script structure and execution, date command usage, variables in shell script