Introduction to Unix

Introduction to Unix – CS 21 Lecture 7

Lecture Overview • Regular expressions revisited • emacs versus vi • Basic emacs and vi usage

Back To Regular Expressions • You will see regular expressions pop up over and over again • Important to understand how they work • Always important to keep in mind that syntax can change, but the meaning will be the same • grep syntax is just as good as any

Guidelines On Constructing Regular Expressions • Break it up piece by piece • If asked for a regular expression that finds two things, try to come up with regular expressions that find each individually • Combine multiple R.E.’s with “or” (|) • If I want all lines with “hello” in them, and you have two expressions that find different instances, one expression with an or will get all of them

Example • Find all instances of dog but not dogs • “dog[^s]” • finds at the beginning or middle • “dog$” • finds at the end • “(dog[^s])|(dog$)” • finds all instances

More Guidelines • Think about all cases • Beginning, middle, and end of the line • Think about what else is important on the line • If I ask for lines that start with “a” and end with “e”, also think about what could go in the middle

In-Class Exercise • Come up with regular expressions for the following: • All lines that have a phone number in it • 909-992-1101 or 123-4567 • All lines that contain the word “lean” but not the word “cleans” • All lines that start with “And” and don’t end with “of”

In-Class Exercise Discussion • “[0-9][0-9][0-9]-[0-9][0-9][0-9][0-9]” • “[0-9]{3}-[0-9]{4}” • ([^c]lean[^s])|(^lean)|(lean$) • (Ând.*[^f]$)|(Ând.*[ô]f$)

Actually Creating And Modifying Files • Good News • Multiple editors in Unix exist that allow you to create and modify text files • Bad News • You will have to get used to and memorize a whole bunch of commands in order to use them well

Editors In Unix • vi • The “visual” editor • vim = “vi improved” • emacs • “editor macros” • “A way of life”, not just an editor

“Holy War” • The choice between emacs and vi divides a large part of the Unix community • No real answer as to which is better, just which you prefer to use • Most likely what you started out with • People, will argue endlessly over why one is better than the other

Why Would You Use vi? • Quick and small • Ready to use immediately and it doesn’t consume too many resources • Simple • No hassles, but quite a few features that are helpful • Always there • vi is virtually guaranteed to be on every Unix system, emacs isn’t

Why Would You Use emacs? • Large • Specialized • Modes exist that help you out for many different types of files • Powerful • Allows you to integrate a lot of work from the shell without leaving the editor • Fast (relatively)

Which One Should You Choose? • Whichever one you feel comfortable with • Both will be introduced here and you will see the differences • Try them both and figure out which suits you best

Unix Editors Versus Windows Editors • vi knows nothing about the mouse • vi doesn’t have any menu options either • If emacs is run inside a terminal window, then the mouse is useless as well • All conveniences can be done through keystrokes, not through mouse operations

Modes Of vi • vi is a modal program • The same key means different things depending on what mode you are in • vi always begins in “command mode” • You won’t be able to type in any text until you change modes • “Esc” will get you into command mode

vi Basics • Starting vi • Usage: vi [FILE] • Quitting vi • Esc, :q

emacs Essentials • Always able to enter text • Commands are given by combinations of control keys • Cntrl • Meta • Usually “Alt” • Sometimes “Esc” (Solaris, etc.)

emacs Basics • Starting emacs • Usage: emacs [FILE] • Quitting emacs • Cntrl-x, Cntrl-c • Book specifices Cntl-x, Cntl-h, Ctnrl-h, Cntrl-h but that doesn’t work on our system

Opening A File In vi • In command mode, hit :e FILENAME • This will abandon you previous file

Opening A File In emacs • Cntrl-x, Cntrl-f • This will switch you to a new file, but will not abandon your previous file

Moving Around In vi • With vim, the arrow keys, page up, and page down work just fine • On some systems, you will need to use special keys in command mode • Cntrl-f = page down • Cntrl-b = page up • h, j, k, l = work like the arrow keys • Left, down, up, right respectively

Specific Movement Commands In vi • w = move forward one word • b = move backward one word • 0 = move to the beginning of a line • $ = move to the end of the line • Cntrl-u = move up half a page • Cntrl-b = move down half a page

Moving Around In Emacs • Arrow keys and page up, page down work fine • Special keys exist just in case • Cntrl-f = one character forward • Cntrl-b = one character backward • Cntrl-v = Page Down • Meta-v = Page up

Special Movement Commands In emacs • Meta-f = move forward one word • Meta-b = move backward one word • Cntrl-a = move to the beginning of the line • Cntrl-e = move to the end of the line • Meta-a = move to the beginning of a sentence • Meta-e = move to the end of a sentence

Simple Searching In vi • In command mode, type “/” followed by the word you are looking for • To go to the next occurrence, in command mode type “n” • Search forwards • “N” will go to previous occurrences in the file • Search backwards

Simple Searching In emacs • Cntrl-s • Type in the word you are searching for • Searches the file forwards • Cntrl-S again will move you to the next occurance • Cntrl-r • Works exactly the same way, but searches backwards through the file

Inserting In vi • First, make get into “insertion mode” • i = transfer into insertion mode • o = transfer into insertion mode in a new line below the current line • O = transfer into insertion mode in a new line above the current line • Now type as normal

Inserting In emacs • Just type as normal • I see this as the biggest advantage emacs has over vi • No special command is needed to start inserting text • Combined with the menus, emacs is a little easier for beginners to handle

Deleting In vi • x = delete one character • dw = delete one word • dd = delete one line • d10 = delete 10 more lines (11 actually)

Deleting In emacs • Cntrl-d = delete one character • Meta-d = delete next word • Cntrl-k = delete one line

Cut And Pasting In vi • Whatever was just deleted is available to be pasted • Word, character, or block of lines • In command mode, “P” will paste most recently cut object

Cut And Pasting In emacs • As long as you are deleting lines with Cntrl-k, those lines can be pasted somewhere else • Cntrl-y will paste most recently cut lines

Saving Changes In vi • In command mode, hit “:w” • If you want to quit without saving changes, you need to the command “:q!”

Saving Changes In emacs • Cntrl-x, Cntrl-s • If you want to exit without saving changes, Cntrl-x, Cntrl-c as normal and then you will be prompted on if you really want to do that

Emacs Backup Files • Emacs will automatically backup the last version of a file whenever you save new changes • Example~ • Whenever a problem occurs, another file gets created • #Example#

Next Time • We go into a lot more depth with emacs and vi • A lot of tricks that come in handy will be presented

Introduction to Unix – CS 21