MacOS – Changing the command prompt of Terminal

You should surround your non-printing characters (in this case, your ANSI escape sequences) with bash escape sequences: \[ and \]. That way bash will know the enclosed characters are not visible, ie. they do not take space, ie. they should not be included in the word-length calculation used by the line-wrapper.

in other words change your PS1 definition:

export PS1="\e[31m\u\e[0m@\e[34m\h\e[33m\w\n \$ \e[0m "

… to:

export PS1="\[\e[31m\]\u\[\e[0m\]@\[\e[34m\]\h\[\e[33m\]\w\n \$ \[\e[0m\] "

And here's the same PS1 value, for human–reading only, with perhaps improved readability (ANSI-escapes in the lower row, bash escapes in the middle and printing characters in the upper row.)

          \u          @          \h          \w\n \$
\[      \]  \[     \] \[      \]  \[      \]        \[     \] 
  \e[31m      \e[0m     \e[34m      \e[33m            \e[0m    

Further reading:

• Bash Prompt HOWTO § 6.1. Colours
• Funtoo: Prompt Magic
• SuperUser: Do I need to enclose ANSI escape sequences in \[ and \] in a bash prompt?

Typically on Mac OS X, only .bash_profile is executing when starting a new terminal. A common solution is to source one file into the other, for example in ~/.bashrc:

[ -r ~/.bash_profile ] && source ~/.bash_profile

Apart from that, your example works perfectly fine for me when put in .bash_profile. If you still experience problems, maybe you are overlooking something else?