Shell Learning Notes (i)

1.

1) Integer calculation:

(1)

$ (()): for mathematical calculations

echo $ ((3+3))

(2)

Expr: There must be spaces on either side of the operator, if $[] is included, you do not have to consider whitespace issues

Expr 2 + 2

2) floating point calculation:

BC for calculating floating-point numbers

Bc-q

Echo ' "3.44*5" |BC '

2. Defining arrays

x= (1 2 4 100 5)

X[3] = 20

(1) Output all echo ${x[*]}

(2) Number of output arrays:

${#x [*]}

${#x [@]}

(3) array element substitution:

Echo ${X[@]/100/3}

3.

(Variable name = variable name + constant/variable)

(variable name **n): The n-th-square of a variable

unset variable name: Delete variable

Unset X[0]

4. Generate random numbers, use $$ as placeholders

Random = $$

Echo $Random

5. Time Performance Comparison

Time echo {1,100}

Time Echo SEQ 100

Time SEQ 100

6.

No spaces on either side of the pipe

If there are more than one statement in quotation marks, separate them with semicolons

This article is from the "Wang Nimei Adult Road" blog, so be sure to keep this source http://8335914.blog.51cto.com/8325914/1611121

Shell Learning Notes (i)