Shell Learning Notes

#表示该脚本以bash方式运行1. #!/bin/bash# accepts the input and assigns the value to the variable 2. Read variable name               #使用变量3. ${variable name} #此变量只读4. readonly variable name          #删除此变量, cannot delete read-only variable 5. The unset variable name # represents the Pid6 of the current shell. $$# (ESS lower key) command replacement, will execute the knot The fruit is saved 7. var= ' command ' #计算8. Var= ' expr "            #注释9.

10. String     A. ' String '                         #单引号的字符串会原样输出, and the inside of the variable is not valid, and single quotation marks can no longer appear in single quotation marks, escaped also not     B. "String"                         #双引号字的符串, can have variables, can have escape characters     C. Greeting                         #连接字符串      d. ${#string}                       #获取字符中长度     E. ${string:1}/${string1:2}         #截取字符串     f. ' Expr index ${string} str '       #查找字符串 str, return index

11. Array     A. with "()" definition, use the "space" symbol to separate element     B. array[0]= "A"                      #定义指定下标的值, subscript can be discontinuous, subscript no upper limit     C. ${array[0]}                          #获取指定 The underlying value     D. ${array[*]}/${array[@]}       #获取数组所有元素     E. ${#array [*]}/${#array [@]} #获取数组长度     d. ${#array [n]}
    #获取数组指定下标的元素的长度

If...else     A. If [Express] #1. [There must be spaces on both sides], equivalent to if Test Express then command fi then #2. [$a = $b], the judge must also have a space between the command        if     b. If [Express] then Command1        else Command2        fi     c. If [Express] then        command1        elif then        command2        else Command3        fi

Case-  in-Case Express in #表达式可以是变量或常量, followed by in keyword Match1) #匹配值后跟) Command1 #匹配成功后执行命令;;　　#跳出, equivalent to break macth2) Command2;;　　*) #默认匹配值, equivalent to default command5;; Esac #结束符

-For-    var in exp1 exp2 exp3 #表达式用 "" (space) separate do        command    done

. while Whil [Express] #表达式为 true to continue doing command done

Until                                   unitl [Express] #表达式为 false to continue doing command done

Break/continue #跳出 or continue, followed by an integer representing the first layer of the loop

18. Functions A. function Func_name () {#定义函数, function can omit command} #只能返回整数数字, if no return value is specified, the result of the last command execution is returned B. func_name  #调用函数, do not need to add (), function to define C. $ ... $9 ${10} #取参数 before the call, the number of arguments more than 10 need to add {}

19. Input/Outbound redirection A. < input redirection B. > output redirection

20. References to other files a. FileName B. SOURCE FileName

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Shell Learning Notes