Na% man_de% manpage:
((expression))
The expression is evaluated according to the rules described below under ARITHMETIC EVALUATION. If the value of the expression is
non-zero, the return status is 0; otherwise the return status is 1. This is exactly equivalent to let "expression".
[[ expression ]]
Return a status of 0 or 1 depending on the evaluation of the conditional expression expression. Expressions are composed of the
primaries described below under CONDITIONAL EXPRESSIONS. Word splitting and pathname expansion are not performed on the words
between the [[ and ]]; tilde expansion, parameter and variable expansion, arithmetic expansion, command substitution, process sub‐
stitution, and quote removal are performed. Conditional operators such as -f must be unquoted to be recognized as primaries.
Você usa bash para realizar comparações matemáticas e bit a bit e (( )) para realizar comparações mais abstratas (para [[ ]] ), por exemplo
touch test;
if [ -e test ]; then
echo test exists
else
echo test does not exist
fi