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I'm wondering where a new path has to be added to PATH environment variable. I know this is accomplished editing .bash_rc (for example), but it's not clear how to do this.

This way:

export PATH=~/opt/bin:$PATH

or this?

export PATH=$PATH:~/opt/bin

Question 2 (related). What's a workable way to append more paths on different lines? Initially I thought this could do the trick:

export PATH=$PATH:~/opt/bin
export PATH=$PATH:~/opt/node/bin

but it doesn't because the second assignment doesn't only append ~/opt/node/bin, but also the whole PATH previously assigned.

This is a possible workaround:

export PATH=$PATH:~/opt/bin:~/opt/node/bin

but for readability I'd prefer to have one assignment for one path.

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5  
+1 Very useful question! –  Noldorin Jul 16 '12 at 1:16

4 Answers 4

up vote 121 down vote accepted

The simple stuff

PATH=$PATH:~/opt/bin
PATH=~/opt/bin:$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.

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).

If your PATH gets built in a 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.

Where to put it

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?

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:

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".

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.

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In exactly which shell does export var=~ not get expanded? Certainly this is not the case in bash which is the specifically tagged shell in the question. –  mikeserv Jun 23 at 1:29

Linux determines the executable search path with the $PATH environment variable. To add directory /data/myscripts to the beginning of the $PATH environment variable, use the following:

PATH=/data/myscripts:$PATH

To add that directory to the end of the path, use the following command:

PATH=$PATH:/data/myscripts

But the preceding are not sufficient because when you set an environment variable inside a script, that change is effective only within the script. There are only two ways around this limitation:

  • If, within the script, you export the environment variable it is effective within any programs called by the script. Note that it is not effective within the program that called the script.
  • If the program that calls the script does so by inclusion instead of calling, any environment changes in the script are effective within the calling program. Such inclusion can be done with the dot command or the source command.

Examples:

$HOME/myscript.sh
source $HOME/myscript.sh

Inclusion basically incorporates the "called" script in the "calling" script. It's like a #include in C. So it's effective inside the "calling" script or program. But of course, it's not effective in any programs or scripts called by the calling program. To make it effective all the way down the call chain, you must follow the setting of the environment variable with an export command.

As an example, the bash shell program incorporates the contents of file .bash_profile by inclusion. So putting the following 2 lines in .bash_profile:

PATH=$PATH:/data/myscripts
export PATH

effectively puts those 2 lines of code in the bash program. So within bash the $PATH variable includes $HOME/myscript.sh, and because of the export statement, any programs called by bash have the altered $PATH variable. And because any programs you run from a bash prompt are called by bash, the new path is in force for anything you run from the bash prompt.

The bottom line is that to add a new directory to the path, you must append or prepend the directory to the $PATH environment variable within a script included in the shell, and you must export the $PATH environment variable.

More information here

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Guandalino, I'm confused by question 2.

If you say

PATH=~/opt/bin

that's all that will be in your PATH. PATH is just an environment variable, and if you want to add to the PATH, you have to rebuild the variable with exactly the contents you want. That is, what you give as an example to question 2 is exactly what you want to do, unless I'm totally missing the point of the question.

I use both forms in my code. I have a generic profile that I install on every machine I work on that looks like this, to accommodate for potentially-missing directories:

export PATH=/opt/bin:/usr/local/bin:/usr/contrib/bin:/bin:/usr/bin:/usr/sbin:/usr/bin/X11
# add optional items to the path
for bindir in $HOME/local/bin $HOME/bin; do
    if [ -d $bindir ]; then
        PATH=$PATH:${bindir}
    fi
done
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2  
You are right about the example of question 2, it works. Another PATH related issue on my system confused me. Sorry for that. –  Paolo Dec 5 '11 at 0:59

Either way works, but they don't do the same thing: the elements of PATHare checked left to right. In your first example, executables in ~/opt/bin will have precedence over those installed, for example, in /usr/bin, which may or may not be what you want.

In particular, from a safety point of view, it is dangerous to add paths to the front, because if someone can gain write access to your ~/opt/bin, they can put, for example, a different ls in there, which you'd then probably use instead of /bin/ls without noticing. Now imagine the same for ssh or your browser or choice... (The same goes triply for putting . in your path.)

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