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products:ict:linux:shell_scripting:arithmetic

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products:ict:linux:shell_scripting:arithmetic [2023/05/04 17:02] – created wikiadminproducts:ict:linux:shell_scripting:arithmetic [2023/05/04 17:13] (current) – wikiadmin
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 +
 +====== Shell Scripting Arithmetic ======
  
  
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 #!/bin/bash #!/bin/bash
 +
 # Basic arithmetic using let # Basic arithmetic using let
 +
 let a=5+4 let a=5+4
 +
 echo $a # 9 echo $a # 9
 +
 let "a = 5 + 4" let "a = 5 + 4"
 +
 echo $a # 9 echo $a # 9
 +
 let a++ let a++
 +
 echo $a # 10 echo $a # 10
 +
 let "a = 4 * 5" let "a = 4 * 5"
 +
 echo $a # 20 echo $a # 20
 +
 let "a = $1 + 30" let "a = $1 + 30"
 +
 echo $a # 30 + first command line argument echo $a # 30 + first command line argument
  
Line 48: Line 61:
  
 9 9
 +
 9 9
 +
 10 10
 +
 20 20
 +
 45 45
  
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 #!/bin/bash #!/bin/bash
 +
 # Basic arithmetic using expr # Basic arithmetic using expr
 +
 expr 5 + 4 expr 5 + 4
 +
 expr "5 + 4" expr "5 + 4"
 +
 expr 5+4 expr 5+4
 +
 expr 5 \* $1 expr 5 \* $1
 +
 expr 11 % 2 expr 11 % 2
 +
 a=$( expr 10 - 3 ) a=$( expr 10 - 3 )
 +
 echo $a # 7 echo $a # 7
  
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 ./expr_example.sh 12 ./expr_example.sh 12
 +
 9 9
 +
 5 + 4 5 + 4
 +
 5+4 5+4
 +
 60 60
 +
 1 1
 +
 7 7
  
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 In the section on Variables we saw that we could save the output of a command easily to a variable. It turns out that this mechanism is also able to do basic arithmetic for us if we tweak the syntax a little. We do so by using double brackets like so: In the section on Variables we saw that we could save the output of a command easily to a variable. It turns out that this mechanism is also able to do basic arithmetic for us if we tweak the syntax a little. We do so by using double brackets like so:
  
 +<nowiki>
 $(( expression )) $(( expression ))
 +</nowiki>
  
 Here's an example to illustrate: Here's an example to illustrate:
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 #!/bin/bash #!/bin/bash
 +
 # Basic arithmetic using double parentheses # Basic arithmetic using double parentheses
 +
 +<nowiki>
 a=$(( 4 + 5 )) a=$(( 4 + 5 ))
 +</nowiki>
 +
 echo $a # 9 echo $a # 9
 +
 +<nowiki>
 a=$((3+5)) a=$((3+5))
 +</nowiki>
 +
 echo $a # 8 echo $a # 8
 +
 +<nowiki>
 b=$(( a + 3 )) b=$(( a + 3 ))
 +</nowiki>
 +
 echo $b # 11 echo $b # 11
 +
 +<nowiki>
 b=$(( $a + 4 )) b=$(( $a + 4 ))
 +</nowiki>
 +
 echo $b # 12 echo $b # 12
 +
 +<nowiki>
 (( b++ )) (( b++ ))
 +</nowiki>
 +
 echo $b # 13 echo $b # 13
 +
 +<nowiki>
 (( b += 3 )) (( b += 3 ))
 +</nowiki>
 +
 echo $b # 16 echo $b # 16
 +
 +<nowiki>
 a=$(( 4 * 5 )) a=$(( 4 * 5 ))
 +</nowiki>
 +
 echo $a # 20 echo $a # 20
  
 Let's break it down: Let's break it down:
  
 +<nowiki>
 a=$(( 4 + 5 )) a=$(( 4 + 5 ))
 +</nowiki>
  
 This is the basic format. As you can see we may space it out nicely for readability without the need for quotes. This is the basic format. As you can see we may space it out nicely for readability without the need for quotes.
  
 +<nowiki>
 a=$((3+5)) a=$((3+5))
 +</nowiki>
  
 As you can see, it works just the same if we take spacing out. As you can see, it works just the same if we take spacing out.
  
 +<nowiki>
 b=$(( a + 3 )) b=$(( a + 3 ))
 +</nowiki>
  
 We may include variables without the preceding $ sign. We may include variables without the preceding $ sign.
  
 +<nowiki>
 b=$(( $a + 4 )) b=$(( $a + 4 ))
 +</nowiki>
  
 Variables can be included with the $ sign if you prefer. Variables can be included with the $ sign if you prefer.
  
 +<nowiki>
 (( b++ )) (( b++ ))
 +</nowiki>
  
 This is a slightly different form. Here the value of the variable b is incremented by 1 (using the same mechanism illustrated under let). When we do this we don't need the $ sign preceding the brackets. This is a slightly different form. Here the value of the variable b is incremented by 1 (using the same mechanism illustrated under let). When we do this we don't need the $ sign preceding the brackets.
  
 +<nowiki>
 (( b += 3 )) (( b += 3 ))
 +</nowiki>
  
 This is a slightly different form of the previous example. Here the value of the variable b is incremented by 3. It is a shorthand for b = b + 3. This is a slightly different form of the previous example. Here the value of the variable b is incremented by 3. It is a shorthand for b = b + 3.
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 ./expansion_example.sh ./expansion_example.sh
 +
 9 9
 +
 8 8
 +
 11 11
 +
 12 12
 +
 13 13
 +
 16 16
 +
 20 20
  
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 #!/bin/bash #!/bin/bash
 +
 # Show the length of a variable. # Show the length of a variable.
 +
 a='Hello World' a='Hello World'
 +
 echo ${#a} # 11 echo ${#a} # 11
 +
 b=4953 b=4953
 +
 echo ${#b} # 4 echo ${#b} # 4
  
 ./length_example.sh ./length_example.sh
 +
 11 11
 +
 4 4
  
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 print out the result of the expression. print out the result of the expression.
  
 +<nowiki>
 $(( expression )) $(( expression ))
 +</nowiki>
  
 Return the result of the expression. Return the result of the expression.
products/ict/linux/shell_scripting/arithmetic.1683201772.txt.gz · Last modified: 2023/05/04 17:02 by wikiadmin