[Shell] shell operations

Arithmetic Operations

The arithmetic operations mentioned here refer to addition (+), subtraction (-), multiplication (*), Division (/), and remainder (%, you can add parentheses to change the priority and only perform operations on integers (Linux bash shell does not support floating-point calculation by default)

#! /Bin/bashval = 'expr 2 + 2' # the expr parameter must be an integer echo "total value: $ Val "A = 10b =-5C = 'expr $ A + $ B '# + an empty box, otherwise, enter a + B = 10 + 20 echo "A + B = $ C" c = 'expr $ A-$ B 'echo "a-B = $ C" c =' expr $ A \ * $ B '# You must add \ before * to realize multiplication, because * has other meanings echo "a * B = $ C" c = 'expr $ A/$ B 'echo "A/B = $ C" If [$ A = $ b] # there must be a space before and after [] and =, [] Then ECHO "A = B" fiif [$! = $ B] Then # Then needs to start another line. It cannot be in the same line as if echo "! = B "filet" sum = 3 + 6 "Echo $ sumsum = $ (7*8) echo $ sum

There are three ways to perform arithmetic operations in Linux bash shell:

1. Use the let Command

let "sum=3+5"    # sum <- 8let "sum=3*5"    # sum <- 15 let "sum=2/5"    # sum <- 0 let "sum=11/5"   # sum <- 2 let "sum=11%5"   # sum <- 1 let "sum=-6-9"   # sum <- -15let "sum=(-6-9)*5"  # sum <- -75

Note,No space is allowed on the right of the equal sign and on both sides of the operator and bracket.

Ii. Use the expr command

sum=`expr 2 - 5`     # sum <- -3sum=`expr 2 + 5`     # sum <- 7 sum=`expr 3 \* 5`    # sum <- 15sum=`expr 3 / 5`     # sum <- 0 sum=`expr 7 / 5`     # sum <- 1sum=`expr \( 2 - 3 \) \* 6`   # sum <- -6 sum=`expr 2+4`       # sum <- 2+4sum=`expr 2-4*6·     # sum <- 2-4*6sum=`expr 1-(5-8)`   # sum <- 1-(5-8)

Note: The asterisk (*) and the left parentheses (and the right parentheses) must be escaped using a backslash (\).. There must be spaces on the right side of expr and on both sides of operators and parentheses.If compact writing is used (compact format can not escape *, (,), the arithmetic expression is returned.

Iii. Use (...)

sum=$((3+5))           # sum <- 8 sum=$(( 3 - 5 ))       # sum <- -2 sum=$(( 3 * 5 ))       # sum <- 15sum=$(( 7 / 5 ))       # sum <- 1 sum=$(( 7 % 5 ))       # sum <- 2 sum=$(( (1 - 2 )  * 4 ))   # sum <- -4

This writing method is relatively free. You can use a loose or compact format without escaping operators and parentheses.

Boolean operation

#! /Bin/Sha = 10b = 200 #-O or operation or #-A and operation andif [$! = $ B] Then ECHO "$! = $ B: A is not equal to B "fiif [$ A-lt 100-A $ B-GT 15] Then ECHO" $ A-lt 100-A $ B-GT 15: returns true "fiif [$ A-lt 100-o $ B-GT 100] Then ECHO" $ A-lt 100-o $ B-GT 100: returns true "fi