How to realize the Mathematical Operation of Linux Shell script
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Arithmetic operations are essential in any programming language, and shell is no exception.
First, use let, (()) and [] for arithmetic operations
You can use the normal variable assignment method to define a numeric value, which is, it is saved as a string. We can make these variables arithmetic by using operators such as let, (), [], and so on. For example:
The code is as follows:
#! / bin/bash
No1=4 # here no1 is stored as a semantic string
No2=5 # here no2 is stored as a semantic string
Let result=no1+no2
The output of echo $result # is 9
Let no1++ # is equivalent to let no1=no1+1
The output of echo $no1 # is 5
Let no2-- # is equivalent to let no2=no2-1
The output of echo $no2 # is 4
Let no1+=5 # is equivalent to let no1=no1+5
The output of echo $no1 # is 10
Let no1-=5 # is equivalent to let no1=no1-5
The output of echo $no1 # is 5
No1=4 # here no1 is stored as a semantic string
No2=5 # here no2 is stored as a semantic string
Result=$ [no1 + no2]
The output of echo $result # is 9
Result=$ [$no1 + 5] # ubuntu does not work properly, no1 not found
The output of echo $result # is 9
Result=$ ((no1 + 50)) # the $before parentheses cannot be lost, otherwise an error will be reported.
The output of echo $result # is 54
Third, use expr for arithmetic operations
The code is as follows:
Expr is a more advanced operator than the above three operators, which can alert you to advanced operations. For example:
#! / bin/bash
Result= `expr 3 + 4` # instead of using single quotation marks, it is the symbol of the key above the tab key
The output of echo $result # is 7
Every space between result= `expr 3 + 4` # 3 and + sign
The output of echo $result # is 3x4
Note: the methods in 1.5.1 and 1.5.2 can only calculate integers, not floating-point numbers.
Third, use bc for arithmetic operations
Bc is an advanced tool for mathematical operations. This precision calculator contains a large number of options, parameters are usually placed before the specific operation to be performed, and a semicolon is used as a delimiter to pass a bc through sdtin. For example:
Echo "4 * 0.56" | the output result of bc # is 2.24
The code is as follows:
No=54
Result= `echo "$no * 1.5" | bc`
The output of echo $result # is 81.0
Echo "scale=2;3/8" # passes the precision of scale tongue decimal, and the output result is 0.37
No=100
Echo "obase=2;$no" | bc # binary conversion. Target binary is binary, default primitive is 10.
No=1100100
Echo "obase=10;ibase=2;$no" | bc # obase=10,ibase=2
Echo "sqrt (100)" | bc # calculates square root
Echo "10 ^ 10" | bc # squared
-Note: obase is the target base, ibase is the primitive, and by default the primitive is 10. 0.
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