Escaping exclamation mark in shell (negation for if/then construct)?

Question

I often use this directly in a shell to test an outcome for scripting, and it works fine:

$ if [ -d mydirectory ] ; then echo YES ; fi
YES

However, if I want to use the negation using exclamation mark, it fails (well, not really fails, but goes into multiline mode waiting for keyboard input, and I have to escape using Ctrl-C):

$ if [ ! -d makehuman ] ; then echo YES ; if
> 
> ^C
$ if [ \! -d makehuman ] ; then echo YES ; if
> 
> ^C

How can I use the negation exclamation mark directly in a shell?

Answer 1

At the Bash command line, the exclamation point can be escaped with a backslash, just like all special characters. Don't forget the correct if syntax, though!

$ if [ \! -d mydirectory ]; then echo Yay; else echo Nay; fi

Answer 2

It was a syntax error, the above commands should finish with fi not if

$ if [ ! -d mydirectoryNO ] ; then echo YES ; fi
YES

Anyway, I also found this nice related link: The classic test command [Bash Hackers Wiki]