bash - Add directory to $PATH if it's not already there

Has anybody written a bash function to add a directory to $PATH only if it's not already there?

I typically add to PATH using something like:

export PATH=/usr/local/mysql/bin:$PATH

If I construct my PATH in .bash_profile, then it's not read unless the session I'm in is a login session -- which isn't always true. If I construct my PATH in .bashrc, then it runs with each subshell. So if I launch a Terminal window and then run screen and then run a shell script, I get:

$ echo $PATH
/usr/local/mysql/bin:/usr/local/mysql/bin:/usr/local/mysql/bin:....

I'm going to try building a bash function called add_to_path() which only adds the directory if it's not there. But, if anybody has already written (or found) such a thing, I won't spend the time on it.

Answer

From my .bashrc:

pathadd() {
    if [ -d "$1" ] && [[ ":$PATH:" != *":$1:"* ]]; then
        PATH="${PATH:+"$PATH:"}$1"
    fi
}

Note that PATH should already be marked as exported, so reexporting is not needed. This checks whether the directory exists & is a directory before adding it, which you may not care about.

Also, this adds the new directory to the end of the path; to put at the beginning, use PATH="$1${PATH:+":$PATH"}" instead of the above PATH= line.