Should I use "test" or "[" "]" in POSIX shell?

Question

I believe both of the following code snippets are valid in POSIX compliant shell:

Option 1:

if [ "$var" = "dude" ]
then
  echo "Dude, your var equals dude."
fi

Option 2:

if test "$var" = "dude"
then
  echo "Dude, your var equals dude."
fi

Which syntax is preferred and why? Is there a reason to use one over the other in certain situations?

Answer 1

There is no functional difference, making this a purely stylistic choice with no widely accepted guidelines. The bash-hackers wiki has an extended section on classic (POSIX-compliant) test, with a great deal of attention to best practices and pitfalls, and takes no position on which to prefer.

Moreover, the POSIX specification for test -- while it does mark a great deal of functionality obsolescent¹ -- specifies neither form as preferred over the other.

That said, one advantage to test is that it's less conducive to folks bringing in expectations from other languages which result in broken or buggy code. For instance, it's a common error to write [$foo=1] rather than the correct [ "$foo" = 1 ], but folks aren't widely seen to write test$foo=1: It's more visually obvious that test "$foo" = 1 is following the same parsing rules as other shell commands, and thus requires the same care regarding quoting and whitespace.

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^[1] Such as -a, -o, ( and ), and any usage with more than four arguments (excluding the trailing ] on an instance started under the name [).