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Introduction to Unix

by: Betty Kertzmann

Introduction to Unix CS 155

Betty Kertzmann
GPA 3.51


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This 19 page Class Notes was uploaded by Betty Kertzmann on Tuesday September 22, 2015. The Class Notes belongs to CS 155 at Colorado State University taught by Staff in Fall. Since its upload, it has received 46 views. For similar materials see /class/210197/cs-155-colorado-state-university in ComputerScienence at Colorado State University.

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Date Created: 09/22/15
CS155 Shells Lecture 10 Review Use tar and zip to group a set of files into one archive file Use gzip and bzip2 to compress files and archives Use sed to do simple editing on streams of text 5132008 08155 Shells Introduction to Shells The shell manages communication between the user and UNIX Shells also provide facilities for completing tasks more efficiently Environment Variables Shell Variables History Scripting Language 5132008 08155 Shells Environment Variables A variable is a symbol with an associated value Environment variables are special variables that are accessible globaly ie by all programs Environment variables are used to customize the behavior of the OS and many programs They are also accessible to all shells attached to the current login session 5132008 08155 Shells Environment Variables List current environment variables printenv 39 env 5132 Environment Variables List current environment variables Use to reference one of the variables Use doublequotes or no quotes 5132008 08155 Shells Environment Variables o setenv set an environment variable Note Changing PWD does not Change the current directory 5132008 08155 Shells Shell Variables Shell variables are specific to a current shell session A shell is opened when you login but also at other times such as when running typescnpt Some shell variables overlap with environment variables Their values are generally inherited from the environment 5132008 08155 Shells Setting Shell Variables o set can be used to list and Change shell variables Changing prompt immediately changes the shell prompt 5132008 08155 Shells 9 Common Variables history number of lines to keep in history home current working directory on login path list of directories in which to search for executables shell path of the shell executable prompt the text displayed on prompt 39 user the Current username 5132008 08155 Shells 10 OnOff Variables Some shell variables do not have values but affect programs by the existence or lack of existence These variables can be turned on by set var and turned off by unset var 5132008 08155 Shells 11 Quoting and Shell Variables The symbols n and are special symbols interpreted by the shell n references your login name references your current pwd 5132008 08155 Shells 12 Escape Sequences Escape sequences are special characters that stand for difficult to type character codes n new line o t tab Escape sequences are often used with echo or other output functions to format the output string 5132008 08155 Shells 13 login and cshrc files Two files exist to set shell variables upon login login Cshrc login gets execute only when a new terminal session is started Cshrc is executed every time a new shell is opened 5132008 08155 Shells 14 forward If you don t Check your mail on your CS account forward your mail forward file One line in the file email address 5132008 08155 Shells alias o alias sets a string to be equivalent to a command usually with options o unalias removes the alias from a string 5132008 08155 Shells 16 umask o umask sets the default permissions for new files Binary Table The default permissions are specified by a 3 digit number Example umask 017 0179 000 001 111 9 111 110 000 complementthe digits 9 rwx rw So the default permission is urwx gnN 5132008 08155 Shells 17 Your cshrc file A oshro file is a shell script at the beginning of a line signifies that the line is a comment and should be ignored by the shell 5132008 08155 Shells 18 Summary Shells can be customized using Environment and Shell variables To use the value of a particular variable in a command put a at the beginning of the name Shell variables are treated differently inside login and cshrc are shell scripts executed on logging in or starting a new shell 5132008 08155 Shells 19


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