Capturing return code with test []

Question

If I run this:

#!/usr/bin/env bash

simple_return_zero(){
  return 0;
}

simple_return_one(){
  return 1;
}

if [ simple_return_zero ]; then
   echo "we have 0000";
fi

if [ ! simple_return_zero ]; then
   echo "we have not 00000";
fi

if [ simple_return_one ]; then
   echo "we have 11111";
fi

if [ ! simple_return_one ]; then
   echo "we have not 11111";
fi

I get:

we have 0000
we have 11111

I know the above is the wrong code to use, I think this is the right way to do it:

if simple_return_zero; then
   echo "we have 0000";
fi

if ! simple_return_zero; then
   echo "we have not 00000";
fi

if simple_return_one; then
   echo "we have 11111";
fi

if ! simple_return_one; then
   echo "we have not 11111";
fi

and now we get something more expected:

we have 0000
we have not 11111

My question is - why doesn't the test command ( [ ] ) work in this case? Doesn't the test command check for exit codes / return codes???

Answer 1

Doesn't the test command check for exit codes / return codes???

Absolutely not. It performs the test as defined by the text within the brackets, whose syntax can be viewed via help test.

if on its own checks the return code of the command executed.