CODEWITHSUNDEEP
bash
Adrian Cornish
Adrian Cornish

Reputation: 23858

How to write a decimal for loop in bash

How can I write a decimal for loop in bash

I get an error like

((: upgradver=1.00: syntax error: invalid arithmetic operator (error token is ".00")

I am trying something like

upgradever=1.00
newver=1.06
for (($ver=$upgradever; $ver<$newver; $ver+=0.01))
do
    echo "Upgrade to $ver"
done

Upvotes: 3

Views: 1644

Answers (3)

osdreams
osdreams

Reputation: 9

Bash doesn't support floating point numbers, but there is a program BC (Best Calculator) that supports decimal arithmetic. 

upgradever="1.00"
newver="1.06"

for (( i=$(bc<<<"($upgradever*100)/1"); $i<$(bc<<<"$newver/0.01"); i++ )); do
      echo $(bc<<<"0.01 * $i")
done

Upvotes: 1

John1024
John1024

Reputation: 113834

Two approaches:

Using bc

The shell does not do floats but the standard utility bc does. This will do your loop:

upgradever=1.00
newver=1.06

ver=$upgradever
while [ 1 = "$(echo "$ver < $newver" | bc -l)" ]
do
    echo "Upgrade to $ver"
    ver=$(echo "$ver + 0.01" | bc -l)
done

Sample output:

$ bash script.sh
Upgrade to 1.00
Upgrade to 1.01
Upgrade to 1.02
Upgrade to 1.03
Upgrade to 1.04
Upgrade to 1.05

Pure bash solution via switching to hundredths

upgradever=100
newver=106
for ((ver=$upgradever; $ver<$newver; ver+=1))
do
    printf -v version '%s.%02i' "$((ver/100))" "$((ver%100))"
    echo "Upgrade to $version"
done

Output:

$ bash  sscript.sh
Upgrade to 1.00
Upgrade to 1.01
Upgrade to 1.02
Upgrade to 1.03
Upgrade to 1.04
Upgrade to 1.05

Upvotes: 6

BRPocock
BRPocock

Reputation: 13914

In short, you "can't," in the sense that the Bourne shell doesn't "do" floating-point math.

You can, however, use another scriptable tool, like Perl, to do it for you:

 $ver = $(perl -e "print $ver + .01")

see also bc, awk, or other tools.

Upvotes: 2

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