Question

How do I convert a string to a number? The following Bash script does not work as expected.

#!/bin/sh

mynum="0.02"

if [[ $mynum -lt 1 ]];then
    echo "low"
else
    echo "high"
fi

Error message

stack.sh: line 5: [[: 0.02: syntax error: invalid arithmetic operator (error token is “.02”)

Answer 1

The problem is that bash normally only supports integer arithmetic; you will need to punt floating or complex math to dc or bc.

You may be able to cheat in this case:

case $mynum in
0 | 0.* | .* | -*)
    echo low
    ;;
*)
    echo high
    ;;
esac

But this obviously isn’t generally applicable.