Mathematical calculation summary in the shell

The assignment and operation in the shell are all string processing by default. Here are a few special methods for performing mathematical operations in the shell. You can see it later when you use it, huh, huh

1, the wrong method example a) var=1+1 echo $var output is 1+1, tragedy, huh, huh,

b) var=1 var=$var+1 echo $var output The result is 1+1, still tragedy, huh, huh

2, the correct method 1) use let var=1 let "var+=1" echo $var output is 2, this time no tragedy Note: a) After I tested let almost support all the operators, I saw an article on the Internet saying that "let does not support ++, --- and commas, (,) & rdquo;, but I tested self-add, decrement, and parentheses The priority is well supported. b) The power operation should use the "**” c) parameter to directly access the expression, without adding $ d) In general, the arithmetic expression can be without double quotes. However, if there are keywords in bash in the expression, you need to add e) the expression after the let can only perform integer operations

2) use (()) var=1 ((va r+=1)) echo $var The output is 2 Note: (()) is used exactly the same as let

3) Use $[] var=1 var=$[$var+1] echo $var output result bit 2 Note: a) $[] will use the expression in brackets as the mathematical operation to calculate the result and then output b) to access the variable in $[] before adding $ c)$[] support The operator is the same as let, but only supports integer operations

4) Use expr var=1 var=`expr $var + 1` echo $var The output is 2 Note: a) Expression after expr The symbols are separated by spaces. b) The operators supported by expr are: | , &, <, <=, =, !=, >=, >, +, -, *, /, % c) The operators supported by expr need to be escaped using \\ Have:| , &, <, <=, >=, >, * e) expr also supports only integer operations

5) use bc (can perform floating point calculation) var=1 var=` Echo "$var+1"| Bc` echo $var output is 2 Introduction: bc is a simple calculator under linux, support floating point calculation, enter bc in the command line to enter the calculator program, and we want to directly calculate the floating point number in the program Use a simple pipeline to solve the problem. Note: 1) I tested bc to support all operators except the bitwise operator. 2) bc should use scale for precision setting 3) floating point number calculation example var=3.14 var=`echo "scale=2;$var*3"| Bc` echo $var The output is 9.42

6) Use awk (which can be used for floating point calculation) var=1 var=`echo "$var 1"| Awk '{printf("%g",$1*$2)}'` echo $var The output is 2 Introduction: awk is a text processing tool and a programming language, as a programming language. Awk supports a variety of operations, and we can use awk for floating point calculations. Just like bc above, we can call awk directly in the program for floating point calculation through a simple pipeline. Note: 1) awk supports all operators except micro-operators 2) awk has built-in functions such as log, sqr, cos, sin, etc. 3) floating point number calculation example var=3.14 var=`echo "$var 2" ;| Awk '{printf("%g",sin($1/$2))}'` echo $var The output is 1 3. Summary Finally, all the materials that can be collected are read, and finally a set of their own Something, I will see similar problems later, haha~