When you run a command from a UNIX or UNIX-like shell, the shell
looks for the executable file using the directories listed in your PATH
variable as a map. For convenience, adding directories to this
environment variable means you don’t have to go hunting for a file each
time you run it. Following these directions will allow you to add a
directory to the search PATH.
To change your path, you must edit the .profile file in your home
directory. If you are comfortable using the vi editor, you probably
don’t need to read any further. If not, then you can use
TextEdit to edit your .profile.
The default .profile is fairly short. The .profile is read when you
open a Terminal window and each line is executed just like typing a
command into the Terminal window. While this is handy because you can
make any available command run whenever you drop to a shell, we’re
concerned with changing an environment variable, PATH.
In your editor, find the line that starts with export PATH=
and give it a look to make sure it doesn’t already contain the
directory path you’re going to add. Sometimes the PATH variable can get
lengthy, but chances are yours just has a few directories separated by
colons, perhaps something like this:
export PATH=/opt/local/bin:/opt/local/sbin:$PATH
There are a few things to note before making changes. The format of
this line is important. The use of spaces in this command, or their
lack, matters. In particular, there cannot be spaces around the equals
sign or between any of the directories. If there are spaces in the
directory name you want to add, you’ll need to escape the space by
preceeding it with a "backslash or by putting the path in quotes (export
PATH=”/path/here”).
The export= keyword in front of that line has a very
specific purpose. Defining a variable without exporting it makes it
available only to the current shell, not to any subsequent shells. You
may think to yourself that you don’t plan to make any subsequent shells,
but this happens whenever you run a shell script. If the PATH variable
was not exported, when you run a shell script, the PATH would no longer
exist and it is possible that the script would fail.
The $PATH at the end of the example above tacks the previous value of
the variable (if it exists) onto the end of the PATH. By default, this
will add ‘:/bin:/sbin:/usr/bin:/usr/sbin’ to the end of the PATH for
you which is useful because most everything you run from the command
line lives there.
So, to add a new directory to the path, simply add it to the existing
PATH line in .profile being careful to separate it from other
directories there with colons and careful not to introduce unwanted
spaces (everything after the space will be ignored). For example, to
add the directory /mightyq/bin to the PATH shown above, the line could
become any of the following examples:
export PATH=/mightyq/bin:/opt/local/bin:/opt/local/sbin:$PATH
export PATH=/opt/local/bin:/mightyq/bin:/opt/local/sbin:$PATH
export PATH=/opt/local/bin:/opt/local/sbin:$PATH:/mightyq/bin
Note that in the third example the new directory is added to the end
of the PATH. You have the ability to optimize the searches your shell
will do on your behalf each time you run a command by organizing your
PATH logically. Putting less frequently used or really massive
directories later in the path may give you a little performance boost
(although these days things are pretty fast, so you have to be a little
anal to really enjoy this).
If you don’t need a directory in your path, you can reverse the
process by deleting the unwanted directory still taking care to preserve
the no spaces, colon separation rules.
One last note, to test the change you made, you can use the echo
command, but you need to make the shell reload the .profile first.
Assuming you are in your home directory (if not, running ‘cd’ without
any options will take you there), run these commands:
. ./.profile
echo $PATH
The first is a neat little command in that it shows three uses or
interpretations of the period in a single line. The first . is a
shortcut to cause the shell to ’source’ or load the contents of the
subsequent file as itself, in the manner that the shell uses when you
login to a system or start a Terminal window. If you simply executed
these commands like a shell script (bash .profile, for example) you
would start a new shell, that shell would get the variable set, and at
the end of running the .profile script, that new shell would cease to
exist and the newly defined variables would be relegated to the missing
sock universe.
The second period means the current working directory. It’s not
compulsory in any way in this command, but it’s habit from explaining
the dots to folks, so I type it all the time now. In this context, you
could also use ~/.profile as ~ explicitly means your home directory.
The last dot causes the .profile to be hidden from view in a normal
directory listing or Finder view. It doesn’t change the file in any
other way, it just make it invisible and de-clutters your directories.
To see hidden files, you can use ‘ls -a’ and you might be surprised by
what you find.