4 Editing files and Emacs

1. 4 Editing files and Emacs Editing files The Emacs editor

2. Editors • Editors are used to create files of text and to modify their contents • You need an editor for sending email, writing programs and many other tasks • There are many different editors - vi, ed and emacs are common UNIX examples • There are different styles of editor - e.g. line editors and text editors • They are not the same as word processors which are concerned with printed documents (fonts, sizes, etc.)

3. The Emacs Editor • A powerful editor, available on most UNIX systems • It’s a text editor • Complex and extensible - we will only explore a fraction - see tutorial and on-line help facilities for more

4. Emacs conventions • Frequent use of the control and meta keys • control key usually marked control or ctrl • the meta key is usually marked alt • The notation C-x means hold down the control key and simultaneously press the x key (was ^X in previous lectures) • M-y means hold down the meta (alt) key and simultaneously press the y key • If the alt-y combination is taken by the host operating system (for example Windows), you can press the escape (esc) key, release it, and then press the y key

5. Edit window Status line Mini-buffer

6. Starting and quitting • From the UNIX prompt type emacs or emacs filename • The emacs screen is divided into three parts • edit window - large part where the contents of the file are displayed • status line - name of file, how far through you are and whether it needs saving • minibuffer - where commands are entered • C-x C-c to quit (of course). You may be prompted to save files

7. Moving around the file • Your current position in the file is shown by the cursor • Most basic movement is one character or line at a time • use the arrow keys or • C-b backward (left) one character • C-f forward (right) one character • C-p previous line (up one character) • C-n next line (down one character) • Scrolling happens as necessary

8. Can also move in steps of a word, sentence, paragraphs and screen • M-f forwards one word • M-b backwards one word • C-a start of current line • C-e end of current line • M-a start of current sentence • M-e end of current sentence • C-v scroll down one screen • M-v scroll up one screen • M-< move to start of file • M-> move to end of file • C-l refreshes the screen and centers the cursor.

9. Inserting and deleting text • To insert text, position the cursor and type • Type RETURN to enter a new line, otherwise the line will wrap around • DEL deletes the character before the cursor and C-d the character after the cursor. Hold down for repeated operation • M-del and M-d deletes whole words

10. C-k deletes from cursor to end of line. A further C-k deletes the new line character • Mark and then delete a whole area: • C-SPACE at start and move cursor to end. • Make sure you have “Active Region Highlighting” ticked to see the marked region in color! • C-w to delete the marked out region • M-w copies the area without deleting it. • Commands that remove more than one character at a time save the text. It can be yanked back with C-y • Another C-y to yank back another copy • M-y to yank back next previously deleted text • Can use C-w and C-y to move text around

11. File handling • Need to be able to load and save files • C-x C-f finds and loads a file • Prompts for the pathname in the minibuffer • Type the name and press RETURN • Use TAB for filename completion • File is either loaded or created

12. Changes made on screen are not immediately made to the file, they are made to a copy called the buffer • Have to explicitly write them back by saving, C-x s (all files) C-x C-s (current file) (answer y and n to prompts) • Can have more than one file open at a time. C-x C-f also switches between buffers if we give the name of an open buffer. • C-x b swaps to the previous buffer • Save frequently - work will be lost if emacs or the system crashes • Previous version may be backed up in filename~

13. Undoing mistakes • C-x u, C-_, and C-/ undo the previous command • Repeating the undo command takes you further back through the editing history

14. Searching • Need to search for text in a large file • Incremental search • type C-s to search forward. • Type C-r to search backwards • Or enter command M-xisearch-forward or M-xisearch-backwards in the minibuffer (use TAB for command completion) • you can delete the last character in the search string • C-g to quit at any time (this works for any command!)

15. Replacing strings • Change all occurrences of one string of text with another • type M-x and enter query-replace • Or type M-% • enter search and target strings • type y or n at each prompt. ! to replace all • use replace-string to avoid the prompting • M-x then spell-buffer for the spell checker

16. Windows • Can divide the edit window into smaller sub-windows, each with a different document • C-x 2 split horizontally • C-x 3 split vertically • C-x 1 make current window the full window • C-x o move cursor to the next window

17. Modes • Modes configure emacs for different kinds of editing, controlling wrap-around and indenting • M-x then mode name • fundamental-mode • text-mode (gives automatic text wrapping) • c++-mode • May guess mode from the filename suffix • Use TAB for autocompletion

18. Help and the tutorial • C-h for top level help menu • C-h C-h to find out what each menu option means • C-h t for the on-line tutorial • A cheatsheet with most of the key combinations in this lecture is in the module folder

19. Coursework 1 • Deadline: 10th April 4PM. • Covers the first three lectures (and the revision lecture) • It mentions one simple command we haven’t seen. You’ll have to find out how it works.

20. Next Lecture • UNIX processes • How to list them • How to prioritise them • How to schedule them • Parent and Child processes • Signals • What are they for? • Types of signal