4 Editing files and Emacs Editing files The Emacs editor

Editors  Editors are used to create files of text and to modify their contents  You need an editor for sending , 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.)

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

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

Mini-buffer Status line Edit window

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

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-bbackward (left) one character  C-fforward (right) one character  C-pprevious line (up one character)  C-nnext line (down one character)  Scrolling happens as necessary

 Can also move in steps of a word, sentence, paragraphs and screen  M-fforwards one word  M-bbackwards one word  C-astart of current line  C-eend of current line  M-astart of current sentence  M-eend of current sentence  C-v scroll down one screen  M-vscroll up one screen  M-<move to start of file  M->move to end of file  C-l refreshes the screen and centers the cursor.

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

 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

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

 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~

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

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-x isearch-forward or M-x isearch-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!)

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

Windows  Can divide the edit window into smaller sub-windows, each with a different document  C-x 2 split horizontally  C-x 3split vertically  C-x 1make current window the full window  C-x omove cursor to the next window

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

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

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.

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