> 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: