When you enter an invalid command at a bash prompt you get the message-bash: {command}: command not foundWhat does the - at the very beginning signify?
what does the dash `-` before `bash` on 'command not found' errors mean?
bash
It means that it is a login shell.From man bash:A login shell is one whose first character of argument zero is a -, or  one         started with the --login option.(In bash terminology, the zeroth argument is the command name which, in your case, was bash.)  bash uses this as a signal to do login activities such as executing .bash_profile, etc.One way that the dash may be added automatically is if the shell is started with exec.  From the Bash manual:exec [-cl] [-a name] [command [arguments]][...] If the -l option is supplied, the  shell places a dash at  the beginning of the zeroth argument passed to command.ExampleCompare these two attempts to run the command nonexistent.  First without -l:$ exec bash$ nonexistentbash: nonexistent: command not foundAnd, second, with:$ exec -l bash$ nonexistent-bash: nonexistent: command not found