[[

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.

• 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 [eq]ual/[n]ot [e]qual/[g]reater [t]han/[l]ess [t]han/[g]reater than or [e]qual/[l]ess than or [e]qual to the specified number:
  [[ ${{variable}} -{{eq|ne|gt|lt|ge|le}} {{integer}} ]]
• Test if the specified variable has a [n]on-empty value:
  [[ -n ${{variable}} ]]
• Test if the specified variable has an empty value:
  [[ -z ${{variable}} ]]
• Test if the specified [f]ile exists:
  [[ -f {{path/to/file}} ]]
• Test if the specified [d]irectory exists:
  [[ -d {{path/to/directory}} ]]
• Test if the specified file or directory [e]xists:
  [[ -e {{path/to/file_or_directory}} ]]