Linux shell arithmetic operations detailed

This article is mainly to share with you the Linux shell arithmetic operation detailed, There are four ways to summarize the arithmetic operations of the Bash Shell and hope to help everyone.

1. Using Expr external program

Addition R= ' Expr 4 + 5 '
Echo $r

Attention! ' 4 ' + ' 5 ' there should be a space between the three

R= ' Expr 4 * 5 ' # error
Multiplication r= ' expr 4 \* 5 '

2. Use $ (())

r=$ ((4 + 5))
Echo $r

3. Use $[]

R=$[4 + 5]
Echo $r

Multiplication
R= ' Expr 4 \* 5 '
r=$ ((4 * 5))
r=$[4 * 5]
Echo $r

Division
r= ' Expr 40/5 '
r=$ ((40/5))
r=$[40/5]
Echo $r

Subtraction
r= ' Expr 40-5 '
r=$ ((40-5))
r=$[40-5]
Echo $r

Find remainder
r=$[100% 43]
Echo $r

(e.g. 2 of 3)
r=$ ((2 * * 3))
r=$[2 * * 3]
Echo $r
Note: Expr does not have a

4. Using the Let command

Addition:
n=10
Let N=n+1
echo $n #n =11

Multiplication:
Let m=n*10
Echo $m

Division:
Let R=M/10
Echo $r

To find the remainder:
Let R=m%7
Echo $r

By emerges:
Let R=m**2
Echo $r

Although the bash shell has four arithmetic operations, not each of which is cross-platform, it is recommended that expr be used.
In addition, we often have 1 operations in script, the following four methods are available:
m=$[m + 1]
m= ' expr $m + 1 '
m=$ (($m + 1))
Let M=m+1

Shell awk Loop summation

1. Simple summation

$ cat Test.txt 1122334455$ awk ' {sum + = $}; End{print sum} ' test.txt  165

2. Summation of specific columns

$ cat test.txt aa      11bb      22cc      33aa      44dd      55$ awk '/aa/{sum + = $ $}; END {print sum} ' test.txt 55

3. Sum, mean, maximum, minimum

$ cat test.txt aa      11bb      22cc      33aa      44dd      55$ cat test.txt | awk ' {sum + = $}; END {print sum} ' 165$ cat Test.txt | awk ' {sum + = $ '; END {print Sum/nr} ' 33$ cat Test.txt | awk ' BEGIN {max=0} {if ($2>max) max=$2 fi}; END {print Max} ' 55$ cat Test.txt | awk ' BEGIN {min=999999999} {if ($2<min) min=$2 fi}; END {print min} '

awk floating-point arithmetic:

Operation expression: awk ' begin{printf '%.6f\n ', (10/3)} '

Operation Result: 3.333333

PS: The internal arithmetic operators of the shell cannot handle floating-point numbers, so when you need to process floating-point numbers, use an external tool (such as awk)