Pattern: Comparing a string value with a numerical operator
Issue: -
You are comparing a string value with a numerical operator, such as -eq, -ne, -lt or -gt.
In [[ .. ]], this would automatically dereference the string, looking to see if there are variables by that name.
In [ .. ], which you are using, the string is just treated as an invalid number.
If you want to compare numbers, expand yourself (e.g. use $var instead of var). If you are trying to compare strings and not numbers, use =, != \< or \> instead.
Example of incorrect code:
read -r n
if [ n -lt 0 ]
then
echo "bad input"
fiExample of correct code:
read -r n
if [ "$n" -lt 0 ]
then
echo "bad input"
fi