Path Environment Variable – How It Works in Linux

The simple stuff

PATH=$PATH:~/opt/bin

or

PATH=~/opt/bin:$PATH

depending on whether you want to add ~/opt/bin at the end (to be searched after all other directories, in case there is a program by the same name in multiple directories) or at the beginning (to be searched before all other directories).

You can add multiple entries at the same time. PATH=$PATH:~/opt/bin:~/opt/node/bin or variations on the ordering work just fine. Don't put export at the beginning of the line as it has additional complications (see below under “Notes on shells other than bash”).

If your PATH gets built by many different components, you might end up with duplicate entries. See How to add home directory path to be discovered by Unix which command? and Remove duplicate $PATH entries with awk command to avoid adding duplicates or remove them.

Some distributions automatically put ~/bin in your PATH if it exists, by the way.

Where to put it

Put the line to modify PATH in ~/.profile, or in ~/.bash_profile if that's what you have.

Note that ~/.bash_rc is not read by any program, and ~/.bashrc is the configuration file of interactive instances of bash. You should not define environment variables in ~/.bashrc. The right place to define environment variables such as PATH is ~/.profile (or ~/.bash_profile if you don't care about shells other than bash). See What's the difference between them and which one should I use?

Don't put it in /etc/environment or ~/.pam_environment: these are not shell files, you can't use substitutions like $PATH in there. In these files, you can only override a variable, not add to it.

Potential complications in some system scripts

You don't need export if the variable is already in the environment: any change of the value of the variable is reflected in the environment.¹ PATH is pretty much always in the environment; all unix systems set it very early on (usually in the very first process, in fact).

At login time, you can rely on PATH being already in the environment, and already containing some system directories. If you're writing a script that may be executed early while setting up some kind of virtual environment, you may need to ensure that PATH is non-empty and exported: if PATH is still unset, then something like PATH=$PATH:/some/directory would set PATH to :/some/directory, and the empty component at the beginning means the current directory (like .:/some/directory).

if [ -z "${PATH-}" ]; then export PATH=/usr/local/bin:/usr/bin:/bin; fi

Notes on shells other than bash

In bash, ksh and zsh, export is special syntax, and both PATH=~/opt/bin:$PATH and export PATH=~/opt/bin:$PATH do the right thing even. In other Bourne/POSIX-style shells such as dash (which is /bin/sh on many systems), export is parsed as an ordinary command, which implies two differences:

• ~ is only parsed at the beginning of a word, except in assignments (see How to add home directory path to be discovered by Unix which command? for details);
• $PATH outside double quotes breaks if PATH contains whitespace or \[*?.

So in shells like dash, export PATH=~/opt/bin:$PATH sets PATH to the literal string ~/opt/bin/: followed by the value of PATH up to the first space. PATH=~/opt/bin:$PATH (a bare assignment) doesn't require quotes and does the right thing. If you want to use export in a portable script, you need to write export PATH="$HOME/opt/bin:$PATH", or PATH=~/opt/bin:$PATH; export PATH (or PATH=$HOME/opt/bin:$PATH; export PATH for portability to even the Bourne shell that didn't accept export var=value and didn't do tilde expansion).

¹ _{This wasn't true in Bourne shells (as in the actual Bourne shell, not modern POSIX-style shells), but you're highly unlikely to encounter such old shells these days.}

Adding a directory to PATH only makes the executables in this directory available as bare command names. This does not extend to subdirectories.

You can put a loop in your .profile (not .bashrc) to add multiple directories, for example:

for d in ~/tools/*/bin; do
  PATH="$PATH:$d"
done

(You don't need to repeat export: when a variable is exported, it stays exported, and modifications are reflected in the environment).

If you create new directories under tools, this will not be reflected in your ongoing session, only the next time .profile is read. If this is not satisfactory, you can use a different approach: put a single directory such as ~/bin in your PATH, and when you install software, create symbolic links in ~/bin. Stow (or its alternative XStow) is a good way of doing this; see Keeping track of programs for an overview of how this works.