[[

Check file types and compare values. Returns a status of 0 if the condition evaluates to true, 1 if it evaluates to false. More information: https://www.gnu.org/software/bash/manual/bash.html#index-_005b_005b.

[[ $variable ==|!= "string" ]]

[[ $variable ==|=~ pattern ]]

[[ $variable -eq|ne|gt|lt|ge|le integer ]]

[[ -n $variable ]]

[[ -z $variable ]]

[[ -f path/to/file ]]

[[ -d path/to/directory ]]

[[ -e path/to/file_or_directory ]]