bash [[ [a] == [a] ]] not true? square bracket affect compare result

Question

Anyone know why this happens? Is this a bug of bash?

x=\'mnt:[4026532411]\'

[[ $x == $x ]] && echo OK

I am expecting result OK

Answer 1

The unquoted right-hand side of == and != is treated as a pattern, not a literal string. mnt:[4026532411] will match mnt: followed by exactly one of 0, 1, 2, 3, 4, 5, or 6, since the patterns mnt:[4026532411] and mnt:[0123456] are equivalent. To match the lieral string, you need to quote the expansion.

x='mnt:[4026532411]'

[[ $x == "$x" ]] && echo OK