Using Emacs for Fun & Profit. Part 0 : align-regexp

Summary
Column alignment of text in emacs is discussed briefly.

If you're a neat freak about your code then you probably prefer related items to line up so that they can be read easily.  For example the C declarations

RGBA zx_plane_color = {RED,    0.1};     
RGBA zy_plane_color = {GREEN,  0.1};      
RGBA xy_plane_color = {BLUE,   0.1};      
RGBA plane_grid_color = {GREY,   0.5};
RGBA background_color = {WHITE,  1};

are a lot easier to read as when aligned up on the "=" sign

RGBA zx_plane_color   = {RED,    0.1};     
RGBA zy_plane_color   = {GREEN,  0.1};      
RGBA xy_plane_color   = {BLUE,   0.1};      
RGBA plane_grid_color = {GREY,   0.5};
RGBA background_color = {WHITE,  1};

The Emacs command align-regexp can handle situations like this and more. The alignment above is accomplished with the sequence of commands below (assuming that the region covers the declarations to align)

Keystrokes	Action
M-x align-regexp	Emacs responds with "Align regexp:" in the minibuffer.
=	Declarations are aligned

To align the after the commas, repeat the same commands but type "," when prompted for a regexp.

Unfortunately, the default is to align on the first occurrence of the regexp.  In many cases, you want to format a table of data such as

12, 34, 23123,     3939
2343, 344,
343, 33, 232,          2323,  zzzz

The sequence of commands then is

Keystrokes	Action
C-u M-x align-regexp	Emacs responds with "Complex align using regexp: \(\s-*\)" in the minibuffer.
Erase the "\(\s-*\)" and replace with "\(\s-+\)"	Emacs responds with "Parenthesis group to modify (justify if negative) : 1"
Press ENTER	Emacs responds with "Amount of spacing (or column if negative): 1"
Press ENTER	Emacs responds with "Repeat throughout line? (y or n) "
Type "Y" then press ENTER	Text is aligned.

The result is

12,   34,  23123, 3939
2343, 344, 
343,  33,  232,   2323, zzzz

Notice that the number of items in each row can differ.
align-regexp can handle much more complex situations than the ones covered here but I believe that these describe the two most common cases in general.