test

Test command syntax vs hard bracket syntax

Note the older format of the test command:

test EXPRESSION

That is mostly replaced by:

[ EXPRESSION ]

And in some shell flavors such as Bash and ZSH, you can use double brackets which adds some extra functionality you might want.

[[ CONDITION ]]

But note that dash (on Ubuntu) is similar to Bash does not support double brackets. Why does this matter? if you use sh command on Ubuntu, you’ll end up running dash and not bash and so will get a syntax error on double brackets.