Tag: element represents article string output shard for form ber
The role of variables
Forbidden spaces on both sides of the equals sign
For loop
#语法一 for variable in value 1 value 2 value 3 : Do block done # #语法二 the for variable ' command ' do block done # #语法三 for (initial value; loop control ; Variable) do program block done
e.g. Output 3 times Uptime
#!/bin/bash for i in 1 2 3 4 5 does echo "$i-->$ (uptime)" done
e.g. bulk unzip all. tar.gz files under the current folder
#!/bin/bash for i in ' ls./*.tar.gz ' does tar-zxvf $i >/dev/null Done
e.g. seeking 1~100 and
#!/bin/bash #注意变量赋值的时候, = There is absolutely no space on either side sum=0 for ((i=1; i<=100; i++)) do sum=$ (($sum + $i) ) Done echo "1+2+3+...+100= $sum"
Array
The attribute of an array is a set of identical data types
Let's look at two types of data: One is a numeric type, the other is a string type, and although the shell itself is a weak type, it can be so distinguished.
array of numeric types: A pair of parentheses represents an array, and the elements in the array are separated by a "space".
As an example:
Arr_number= (1 2 3 4 5);
array of string types: Similarly, use a pair of parentheses to represent the array, where the elements in the array are enclosed in double or single quotation marks, and also with "spaces."
arr_string= ("abc" "EDF" "SSS"); or arr_string= (' abc ' EDF ' SSS ');
We use the numeric type array arr_number= (1 2 3 4 5) as the source array for the relevant explanation: Get the array length, read the value of a subscript, assign a value to a subscript, delete, assign and replace, and traverse.
The shell looks to get the value of a variable, starting with the $ character, such as: $a or ${a}.
Get array length
arr_length=${#arr_number [*]} or ${#arr_number [@]}, i.e. form: ${#数组名 [@/*]} to get the length of the array.
Reads a value of a subscript
ARR_INDEX2=${ARR_NUMBER[2]}, i.e. form: ${array name [subscript]}
Assign a value to a subscript
Here are two questions to ask:
The first question is , what happens if the subscript element already exists?
A : the underlying value is modified to be the new specified value.
For example: arr_number[2]=100, the array is modified to (1 2 100 4 5)
The second question is , if the specified subscript already exceeds the size of the current array, such as the size of the arr_number above is 5, specify an subscript of 10 or 11 or greater than 5 of any value?
A : the newly assigned value is appended to the end of the array.
For example: arr_number[13]=13, the array is modified to (1 2 100 4 5 13)
Delete operation
Clear an element: unset arr_number[1], this clears the array labeled 1;
Empties the entire array: unset arr_number;
Shard Access
The Shard Access form is: ${array name [@ or *]: start subscript: End subscript}, note that the value of the end subscript element is not included.
For example: ${arr_number[@]:1:4}, where Shard Access starts with subscript 1 and the number of elements is 4.
Mode substitution
Form: ${array name [@ or *]/mode/new Value}
For example: ${arr_number[@]/2/98}
Traversal of an array
Array traversal We use the FOR statement to demonstrate:
For V in ${arr_number[@]}; Do
Echo $v;
Done
Shell Programming-Basic syntax