Как в bash сравнить две строки?

sasha@as255:~$ aa='fdfs'
sasha@as255:~$ bb='ghjkl'
sasha@as255:~$ cc='sfsf'
sasha@as255:~$ dd='fdfs'
sasha@as255:~$ [[ $aa == $bb ]] && echo "true" || echo "false"
false
sasha@as255:~$ [[ $aa == $dd ]] && echo "true" || echo "false"
true
sasha@as255:~$ [[ $aa == $cc ]] && echo "true" || echo "false"
false

man test

man bash

if [ $str1 == $str2 ];
then
echo "Match"
else
echo "Not match"
fi

Thanks Ж:)

> man bash

ls -l `which [`