Linux Shell script strategy (1.5), linuxshell

Linux Shell script strategy (1.5), linuxshell
1.5 use shell for mathematical operations

In any programming language, arithmetic operations are essential, and shell is no exception.

1.5.1 Use let, (), and [] for arithmetic operations

• You can use the normal variable value assignment method to define a value.String. We can use let, (), [], and other operators to perform arithmetic operations on these variables. For example:

#! /Bin/bashno1 = 4 # Here, the no1 string is stored in the form of no2 = 5 # Here, the no2 string is stored in the form of let result = no1 + no2 echo $ result # The output result is 9let no1 ++ # equivalent to let no1 = no1 + 1 echo $ no1 # The output result is 5let no2 -- # equivalent to let no2 = no2-1echo $ no2 # The output result is 4let no1 + = 5 # equivalent let no1 = no1 + 5 echo $ no1 # The output result is 10let no1-= 5 # equivalent to let no1 = no1-5echo $ no1 # The output result is 5 no1 = 4 # Here the no1 literal string format storage no2 = 5 # Here, the result is stored in the form of a no2 string = $[no1 + no2] echo $ result # The output result is 9 result = $ [$ no1 + 5] # In ubuntu cannot run normally, no1 not foundecho $ result # The output result is 9 result = $(no1 + 50) # The $ before the brackets cannot be lost. Otherwise, an error is returned. echo $ result # The output result is 54.

1.5.2 use expr for arithmetic operations

• Expr is a more advanced operator than the preceding three operators, so you can watch for advanced operations. For example:

#! /Bin/bashresult = 'expr 3 + 4' # It is not a single quotation mark, echo $ result # The output result is 7 result = 'expr 3 + 4' # echo $ result every space between 3 and + # The output result is 3. + 4

• Note: Methods in 1.5.1 and 1.5.2 can only calculate integers, but cannot calculate floating point numbers.

1.5.3 perform arithmetic operations using bc

• Bc is an advanced tool for mathematical operations. This precision calculator contains a large number of options. parameters are usually placed before the specific operation to be executed, and the semicolon is used as the delimiter, pass bc through sdtin. For example:

Echo "4*0.56" | bc # output result is 2.24no = 54 result = 'echo "$ no * 1.5" | bc 'echo $ result # output result is 81.0 echo "scale = 2; 3/8 "# The output result is 0.37no = 100 echo" obase = 2; $ no "Based on the scale decimal precision. | bc # converts the target to binary, the default Operating System is 10 no = 1100100 echo "obase = 10; ibase = 2; $ no" | bc # obase = 10, ibase = 2 echo "sqrt (100) "| bc # Calculate the square root echo" 10 ^ 10 "| bc # Calculate the square

-Note: The obase is the target base, and the ibase is the original base. By default, the original base is 10.

1.5.4 reference

Introduction to Linux Shell scripts