'[' is a Bash builtin. See https://www.computerhope.com/unix/bash/index.htm https://www.computerhope.com/unix/bash/index.htm. It is usually also a symlink to

'[' is a Bash builtin. See https://www.computerhope.com/unix/bash/index.htm https://www.computerhope.com/unix/bash/index.htm. It is usually also a symlink to the 'test' executable but not in all Unix-like systems.