Use Shell to write a simple calculator, you can implement add, subtract, multiply, divide operations, if the script name is 1.sh, execute example:./1.

Use Shell to write a simple calculator, you can implement add, subtract, multiply, divide operation, if the script name is 1.sh, execute example:./1.sh 1 + 2

#!/bin/bashif [ $# -ne 3 ]then   echo  "The number of parameters should be 3, for example: $0 1  + 2 "   echo " when using multiplication, you need to add the caret, for example: $0 1 \* 2 "   exit  1;finum1= ' echo $1|sed  ' s/[0-9. G ' if [ -n  "$num 1"  ]then    echo  "$ not number"      exit 1finum3= ' echo $3|sed  ' s/[0-9. G ' if [ -n  "$num 3"  ]then    echo  "$ $ not a number"      exit 1ficase $2 in   +)     echo  "Scale=2;$1+$3"  | bc    ;;    -)     echo  "Scale=2;$1-$3"  | bc    ;;    \*)     echo  "Scale=2;$1*$3"  | bc    ;;    /)     echo  "Scale=2;$1/$3"  | bc    ;;    *)     echo  "$2  not operator"      ;; Esac

Analytical:

Number of $# parameters

The currently executing process name

Num1-ne num2 Not equal to [3-ne $mynum]

-N String if string length is nonzero, true [-n ' $myvar ']

Sed ' "n1,n2" "[0-9a-za-z]" s/source string/target string/g ' filename
Here n1,n2 refers to the interval N1 to N2 line, "s" is the command to replace, "G" for the bank in the global replacement, if not add ' g ', then only the first occurrence of the row. In addition to the use of "/" as a delimiter, you can also use other special words such as "#" or "@".

The BC command is a calculator language that supports interactive execution of arbitrary precision. Bash has built-in support for integer arithmetic, but it does not support floating-point operations, and the BC Command makes it easy to do floating-point arithmetic. The parameter scale=2 is set to 2 bits for the decimal digits of the BC output

Use case, if $ +, output echo "scale=2;$1+$3" | Bc

In turn on pushing

Output echo "$ not operator" If the subtraction is not in either case

Use Shell to write a simple calculator, you can implement add, subtract, multiply, divide operations, if the script name is 1.sh, execute example:./1.