[[
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://gnu.org/software/bash/manual/bash.html#index-_005b_005b.
- Test if a given variable is equal/not equal to the specified string:
[[ $variable ==|!= "string" ]]
- Test if a given string conforms the specified glob/regex:
[[ $variable ==|=~ pattern ]]
- Test if a given variable is equal/not equal/greater than/less than/greater than or equal/less than or equal to the specified number:
[[ $variable -eq|ne|gt|lt|ge|le integer ]]
- Test if the specified variable has a non-empty value:
[[ -n $variable ]]
- Test if the specified variable has an empty value:
[[ -z $variable ]]
- Test if the specified file exists:
[[ -f path/to/file ]]
- Test if the specified directory exists:
[[ -d path/to/directory ]]
- Test if the specified file or directory exists:
[[ -e path/to/file_or_directory ]]