Numbers and Arithmetic in bash: Difference between revisions

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Line 5: Line 5:
=How to Tell if a Variable has an Integer Value=
=How to Tell if a Variable has an Integer Value=


<pre>
<syntaxhighlight lang='bash'>
v=10
v=10


Line 17: Line 17:
     #
     #
fi
fi
</pre>
</syntaxhighlight>
 
More details: {{Internal|expr|expr}}
 
=Integral Number Operations=
 
==$((...))==
 
<syntaxhighlight lang='bash'>
op1=4
op2=2
echo $((op1 + op2))
echo $((op1 - op2))
echo $((op1 * op2))
echo $((op1 / op2)) # integral division
echo $((op1 % op2)) # modulo
</syntaxhighlight>
displays:
<syntaxhighlight lang='bash'>
6
2
8
2
</syntaxhighlight>
<syntaxhighlight lang='bash'>
echo $(($(date '+%s') % 2))
</syntaxhighlight> also works.


More about {{Internal|expr|expr}}
==expr==
{{Internal|expr|expr}}
 
==bc==
<syntaxhighlight lang='bash'>
local t0="$(date -u +%s)"
local t1="$(date -u +%s)"
local delta="$(bc <<<"${t1}-${t0}")"
</syntaxhighlight>


=Floating Point Operations=
=Floating Point Operations=
Line 25: Line 59:
Multiplication:
Multiplication:


<pre>
<syntaxhighlight lang='bash'>
local operand1=10.1
local operand1=10.1
local operand2=20.2
local operand2=20.2


result=$(echo ${operand1} ${operand2} | awk '{printf "%5.1f\n",$1*$2}') || exit 1
result=$(echo ${operand1} ${operand2} | awk '{printf "%5.1f\n",$1*$2}') || exit 1
</pre>
result=$(echo ${operand1} ${operand2} | awk '{printf "%.1f\n",$1*$2}') || exit 1
</syntaxhighlight>


Division:
Division:


<pre>
<syntaxhighlight lang='bash'>
local operand1=10.1
local operand1=10.1
local operand2=20.2
local operand2=20.2


result=$(echo ${operand1} ${operand2} | awk '{printf "%5.1f\n",$1/$2}') || exit 1
result=$(echo ${operand1} ${operand2} | awk '{printf "%5.1f\n",$1/$2}') || exit 1
</pre>
</syntaxhighlight>


=Increment an Integer=
=Increment an Integer=
{{Internal|((...))#Increment_an_Integer|Increment an Integer with ((...)) operator}}
{{Internal|((...))#Increment_an_Integer|Increment an Integer with ((...)) Operator}}


=Decrement an Integer=
=Decrement an Integer=
Line 52: Line 87:
a=1
a=1
b=2
b=2
if [[ $((a - b)) -lt 0 ]]; then
  ...
fi
if [[ $(expr ${a} - ${b}) < 0 ]]; then
if [[ $(expr ${a} - ${b}) < 0 ]]; then
   ...
   ...

Revision as of 04:56, 1 July 2021

Internal

How to Tell if a Variable has an Integer Value

v=10

if expr ${v} + 1 >/dev/null 2>&1; then
    #
    # the value contained by v is an integer
    #
else
    #
    # the value contained by v is NOT an integer
    #
fi

More details:

expr

Integral Number Operations

$((...))

op1=4
op2=2
echo $((op1 + op2))
echo $((op1 - op2))
echo $((op1 * op2)) 
echo $((op1 / op2)) # integral division
echo $((op1 % op2)) # modulo

displays:

6
2
8
2
echo $(($(date '+%s') % 2))

also works.

expr

expr

bc

local t0="$(date -u +%s)"
local t1="$(date -u +%s)"
local delta="$(bc <<<"${t1}-${t0}")"

Floating Point Operations

Multiplication:

local operand1=10.1
local operand2=20.2

result=$(echo ${operand1} ${operand2} | awk '{printf "%5.1f\n",$1*$2}') || exit 1
result=$(echo ${operand1} ${operand2} | awk '{printf "%.1f\n",$1*$2}') || exit 1

Division:

local operand1=10.1
local operand2=20.2

result=$(echo ${operand1} ${operand2} | awk '{printf "%5.1f\n",$1/$2}') || exit 1

Increment an Integer

Increment an Integer with ((...)) Operator

Decrement an Integer

Decrement an Integer with ((...)) Operator

Numeric Evaluation in a Condition

a=1
b=2

if [[ $((a - b)) -lt 0 ]]; then
  ...
fi

if [[ $(expr ${a} - ${b}) < 0 ]]; then
  ...
fi

Random Numbers

Bash script that generates a random MAC address