Emacs has an interactive regex mode that shows matches as you type.

To go into the mode, M-x regexp-builder.  Type C-c C-q to exit the mode.

Watch out for escape characters.  Emacs requires you to escape \, so type \b for \b

Copy the following text into emacs and then M-x regexp-builder

Lots of Grey things
50 shades of Grey
Earl Grey Tea
Lady Grey
Graybeard the pirate
Greyhound buses
"You're looking grey," he said.
"That's the greyest greyhound I ever saw," said Earl Grey.
Grey1: Dark Gray
Grey35: Mid grey
Grey44: Battleship grey
Grey100: The colour of TV tuned to a dead channel

In regexp-builder, type…

Grey to find all the Greys
Gray to find all the Grays
Gr[ae]y to find all the Greys and Grays
\\bGray\\b to find Gray on its on and not part of another word
^Gray to find lines beginning with Gray
grey$ to find lines ending in grey
grey\\(hound\\)? to find all appearances of grey and greyhound
grey[0-9] to find all the shades of grey ending with a digit
grey[0-9]\\{2\\} to find all the shades of grey with exactly two digits

Follow the link for some Regexp Exercises to try out

Read more about Regexps at the Emacs Wiki

I never use the rectangle commands as often as I should.

Here’s my shopping list:

• Bread
• Cheese
• Milk
• Yoghurt

I want to make the above into a list. There are all sorts of ways I could so this, one way is to use the string-rectangle command. Set (or highlight) the region to zero width in front of the list and then C-x r t – to insert a dash before each of the words.

You can use the kill-rectangle command to remove unwanted bullet points (particularly useful when importing text from PDFs)

Set the region to cover the bullet symbols and then C-x r k to kill the rectangle. Don’t forget you can C-x r y yank that rectangle back.

C-x r o or open-rectangle is a quick way to indent a block of text to where you want it, especially if you can’t remember the other commands.

And lastly C-x r c will clear a rectangular space. I can’t remember ever using that one, to be honest…

If you find pressing C-x r a keystroke too far, read this post on remapping C-x r  to C-`

Summary of Commands

C-x r k    Kill rectangle
C-x r y     yank last killed rectangle
C-x r c     Clear rectangle
C-x r o     open rectangle and shift text right
C-x r t spoons  fill rectangle with spoons
C-x r r q   Copy rectangle to register q
C-x r i q   Insert rectangle from register q

Many people say that once you get the hang of Dired, you never use anything else. How true is this?

From a personal perspective I’d say that was true, but the key is in the first part of the sentence once you’ve got used to using Dired…

Here’s real world use for Dired.

C-x d to start Dired and navigate to a directory.

Here’s a directory into which a CD has been ripped. The track names haven’t been recognised.

/home/*****/Music/Ludwig van Beethoven/Beethoven- Symphonies Nos. 1 & 2:
total used in directory 108088 available 32870008
drwxrwxrwx 2 ***** ***** 4096 Jun 8 2009 .
drwxrwxrwx 4 ***** ***** 4096 Jan 10 2009 ..
-rwxr--r-- 1 ***** ***** 19510080 Sep 21 2010 01 Track 1.mp3
-rwxr--r-- 1 ***** ***** 12268125 Sep 21 2010 02 Track 2.mp3
-rwxr--r-- 1 ***** ***** 7567075 Sep 21 2010 03 Track 3.mp3
-rwxr--r-- 1 ***** ***** 11410580 Sep 21 2010 04 Track 4.mp3
-rwxr--r-- 1 ***** ***** 20195615 Sep 21 2010 05 Track 5.mp3
-rwxr--r-- 1 ***** ***** 19836565 Sep 21 2010 06 Track 6.mp3
-rwxr--r-- 1 ***** ***** 7501945 Sep 21 2010 07 Track 7.mp3
-rwxr--r-- 1 ***** ***** 12329080 Sep 21 2010 08 Track 8.mp3

I could rename each track using a GUI by right clicking on each one and changing the name. Dired mode is faster

C-x C-q to toggle read only. Now simply type the new names of the tracks directly into the buffer. C-c C-c when you’ve finished.

If you want to be more efficient, move the point to the T in Track 1 and press M-z 1 to zap-to-char 1, deleting everything up to including the 1, leaving the .mp3 intact. Now type in the new track name.

If you want to be really efficient, of course, you could use search and replace…

Related Posts

Dired Tricks #2

The key to snooker isn’t where the coloured balls go, it’s where your white ball stops. You should always be thinking about setting up your next shot. Something similar holds when using Emacs. Where will the point (cursor) be when you’ve completed your current operation?

Consider the following commands:
M-u Convert to uppercase to the end of the word
M-l Convert to lowercase to the end of the word
M-c Capitalize word

Note that the point jumps to the end of the word when each command is called. This makes it easy to jump through a string of words, changing case or capitalizing as you wish.

Now consider the following

M– M-u Convert previous word to uppercase
M– M-l Convert previous word to lowercase
M– M-c Capitalize previous word
M– means (Alt) and –

Note that the point remains where it is, at the end of the word you’ve just converted. You can’t jump back through a series of words converting as you go.

It’s like the difference between hitting C-o and hitting Enter. At first glance they both appear to do the same thing, but look at the point…
(image: www.freeimages.co.uk)