and other binary operators such as

• = and != (string)
• -le and -gt, and so forth (arithmetic)

if [ ! "$var" -eq 1 ]; then :; fi
if ! [ "$var" = foo ]; then :; fi

if [ "$var" -ne 1 ]; then :; fi
if [ "$var" != foo ]; then :; fi

Double negation of such binary operators is unnecessary.

This is a stylistic issue that does not affect correctness. If you prefer the original expression, you can Ignore it with a directive or flag.

This rule is not applied to the followings:

• < and > (lexicographical)
• -nt and -ot (file timestamp)
• =~ (regular expression)

• Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!
• SC2236 and SC2237 for unary operators -n and -z