100 Useful Command-Line Utilities

by Oliver; 2014

103. Bonus: Global Variables

To see all global variables, type:

$ set

Where bash looks for commands and scripts:

$PATH

Add a directory path to the back of the path:

$ PATH=$PATH:/my/new/path

Add a directory path to the front of the path:

$ PATH=/my/new/path:$PATH

Now we know where to put bash commands, but what about other programs? What if you've installed a package or a module in a local directory and you want the program to have access to it? In that case, the following global variables come into play.

Where matlab looks for commands and scripts:

$MATLABPATH

Where R looks for packages:

$R_LIBS

Where awk looks for commands and scripts:

$AWKPATH

Where Python looks for modules:

$PYTHONPATH

Where Cpp looks for libraries:

$LD_LIBRARY_PATH

Where Perl looks for modules:

$PERL5LIB

This will come into play when you've locally installed a module and have to make sure Perl sees it. Then you'll probably have to export it. E.g.:

$ export PERL5LIB=/some/path/lib64/perl5

Text editor:

$EDITOR

You can set this by typing, e.g.:

export EDITOR=/usr/bin/nano

Then Control-x-e will invoke the text editor.

The specially designated temporary directory:

$TMPDIR

A shell variable that stores a random number for you:

$RANDOM

For example:

$ echo $RANDOM
1284
$ echo $RANDOM
27837

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