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Unix Introduction
¯ These notes partly based on
– CS 211 lecture notes
– UWO CS department Unix introduction
1
Unix: Power to the Expert
¯ Unix: intended for expert computer users
– Steep learning curve
– Difficult for first-time computer users
– Easy and powerful, once learned
¯ Terse, “cute” command names
¯ When not running an editor or an application, you will spend most of your time on Unix
– Interacting with a “shell” (command interpreter program)
– Running “utility commands”
¯ In X window system (Cygwin), select “shell” from menu to get a shell window
2
Shells
¯ Several different versions of shell: sh, csh, tcsh, bash, . . .
¯ As soon as you log in, you will be interacting with an instance of your default shell
– To find what your default shell is:
– Issue command finger username
where username is your username
– What is listed after Shell: is your default shell
¯ You may have a different default shell on GAUL and RENT
¯ To run a different shell instance on top of your current shell instance, type its name (e.g.
bash)
¯ To exit a shell, type exit or logout
¯ For the rest of this tutorial, we will assume bash
3
Editing Files: pico
¯ Easiest editor to use: pico
¯ To start editing new or existing file: pico fname
¯ File name at top of screen
¯ Some commands described at bottom of screen
¯ Type letters to enter them into the file
¯ Use arrow keys to navigate around the file
¯ Control-X to exit and save changes
¯ Google pico editor for help on the Web
4
Getting Help: man
¯ man command
– Gives “manual page” (help information) about command
¯ man -k keyword
– Prints list of all manual pages that contain keyword in title or brief description
5
Basic Unix Commands
¯ Available in all shells
¯ Simple commands
¯ Displaying files
¯ Copying, renaming, removing files
¯ Directories
¯ Moving around and creating directories
¯ Listing directory contents
¯ More copying, renaming, removing
6
Some Simple Commands
¯ echo text
– Just displays text on window
¯ ls
– Lists files in current directory
¯ touch fname
– If fname did not exist, creates it as empty file
– If fname did exist, leaves it the same
¯ history
– Gives history of all past commands since shell created
7
Displaying Files
¯ cat fname
– Types the file on the window containing the shell
¯ cat fname1 fname2 . . . fnameN
– Types all those files on the window containing the shell
(cat is short for “concatenate”)
¯ more fname
– Displays as much of the file as can fit in the window
– If more of the file exists, says “more”
– Type space to get next “page” of the file
– Type q to quit
¯ more fname1 fname2 . . . fnameN
– Displays those files one by one
8
Copying, Renaming, Removing Files
¯ cp fname1 fname2
– Copies entire contents of file fname1 to fname2
– If fname2 did not exist, creates it
– If fname2 did exist, replaces it with new contents
¯ mv oldfname newfname
– Renames file oldfname to newfname
– If newfname existed before, replaces it
¯ rm fname
– Removes file completely
9
Directories
¯ Files organized into tree of directories
¯ Root directory of entire file system: “/”
¯ Every file has an full path name: complete unique identification relative to root directory
– e.g. /csd/faculty/einstein/courses/unixIntro/unixA.txt
¯ You are always in a current working directory
– e.g. /csd/faculty/einstein/courses/unixIntro/
¯ You can refer to files in working directory without giving full path name
– e.g. unixA.txt
¯ You have a default “home directory”
– Your working directory when you first log in
¯ /tmp
– Directory for temporary files; everyone can create files there
– All files deleted when system reboots
10
Moving Around and Creating Directories
¯ pwd
– Prints working directory
¯ cd dirname
– Changes your working directory to dirname
¯ cd
– Changes your working directory to your home directory
¯ mkdir dirname
– Makes new directory in the working directory
¯.
– Single dot: always same as working directory
¯ ..
– Double dot: always same as parent directory of working directory
– Thus, cd .. takes you to parent directory
11
Listing Directory Contents: ls
¯ ls
– Lists files and directories inside working directory
¯ ls fname
– Lists just that file name, if file exists
¯ ls fname1 fname2 . . . fname3
– Lists all those file names, if files exist
¯ ls dirname
– Lists contents of that directory
¯ ls -l
– Lists details of files and directories inside working directory
¯ ls -l fname1 fname2 . . . fname3
– Lists details of those files
¯ ls -l dirname
– Lists details of all files in that directory
12
Listing Directory Contents: ls
¯ ls -a . . .
– Lists all files, including those whose names start with “.”
¯ ls -F . . .
– Indicates what kind of file each file is: directory, executable, etc.
¯ ls -R . . .
– Lists contents recursively down to leaf nodes
¯ ls -t . . .
– Sorts files by last modification time instead of name
13
More Copying, Renaming, Removing
¯ cp fname dirname
– Copies that file into that directory
¯ cp fname1 fname2 . . . fnameN dirname
– Copies all those files into that directory
¯ mv fname dirname
– Moves that file into that directory
¯ mv fname1 fname2 . . . fnameN dirname
– Moves all those files into that directory
¯ rm -r dirname
– Removes that directory and everything in it
14
Searching: grep
¯ grep string fname
– Searches for string in file fname
¯ grep string fname1 fname2 . . . fnameN
– Searches for string in all files
¯ grep -i string fname
– Ignores the case (uppercase / lowercase) of the string
¯ grep -w string fname
– Searches for string standing alone as a word
¯ Many more options (see man grep for details)
¯ grep is short for “get regular expression and print”
15
Shell Input Processing
¯ Every command you give to the shell is processed first
– If you use certain special characters, parts of your command will be replaced by other
things
¯ Most non-alphanumerics are “special”! Including:
! # $ % & * | ~ ‘ ; " ’ < > ?
– Not a good idea to use these or spaces in any file name
– Safe to use the following in file names:
_ - + = .
16
Star Character
¯ * character: for accessing patterns of file names
¯ Examples:
– *.java
– Shell replaces this with a space-separated list of all file names in working directory
that end in “.java”
– myapp*
– Shell replaces this with a space-separated list of all file names in working directory
that start with “myapp”
¯ Thus:
– ls myapp*
– Lists all files in working directory that start with “myapp”
– mv *.java src
– Moves all files in working directory that end with “.java” to directory src (if it
exists)
17
Bang (Exclamation Mark) Character
¯ ! character: for accessing patterns of previous commands
¯ Examples:
– !!
– Shell replaces this by the last command issued
– !cd
– Shell replaces this by the last cd command issued
– !javac
– Shell replaces this by the last javac command issued
18
Tilde Character
¯ ~ character: for accessing users’ home directories
Examples:
– ~einstein
– Shell replaces this by name of home directory of user einstein
– ~curie
– Shell replaces this by name of home directory of user curie
–~
– Shell replaces this by name of your home directory
¯ Thus:
– ~/bin
– Name of directory bin inside your home directory
19
Dollar Sign and Shell Variables
¯ Shell has arbitrary number of untyped variables
– Don’t have to declare them
– They always have values that are sequences of characters
¯ Assign a shell variable a value e.g. with
UNIVERSITY=Western
¯ Then, shell replaces string $UNIVERSITY in commands by Western
¯ If you use e.g. $UNIVERSITY without variable UNIVERSITY being given a value, then
shell complains
¯ export varname
– After you do this, programs that you run will be able to find value you set for varname
20
Echo Revisited
¯ echo any text
– Just prints the words it is given as parameters
– Shell processes that command just like any other command
¯ Try these commands:
echo *.java
echo myapp*
echo !!
echo !cd
echo $PATH
21
Running Programs
¯ First sequence of nonblank characters you type in a command: command name
¯ If command name is a shell command, shell executes that command
¯ If not, then the shell:
– Looks for a file with that name
– Interprets it as an executable file
– Tries to execute that file
¯ Where does it look?
– On each directory listed on your “path”
– Your “path” contained in shell variable $PATH
– Colon-separated list of directory names
¯ Typical PATH:
/usr/local/bin:/usr/ucb:/usr/bin:/bin:/usr/X11/bin:.
22
Breaking Programs
¯ If it looks like a program is hanging, type control-C in the shell window where you
launched it
– May cause program to terminate
23
Unix I/O
¯ Standard input and output
¯ Default standard input and output
¯ Redirecting standard input and output
¯ Behaviour of Unix commands
¯ Piping output from command to command
24
Standard Input and Output
Standard Input Standard Output
Unix
(stdin) (stdout)
Program
¯ Here “Unix program” can be a built-in command, system program or program written by
user
¯ Standard output (stdout): where printf for C programs goes
– Most Unix utilities write something to stdout
¯ Standard input (stdin): where data for scanf, gets, etc. for C programs comes from
– Some Unix utilities read from stdin in some cases
25
Default Standard Input and Output
Keyboard
Displayed
(typed into Unix
on shell window
shell window) Program
¯ By default, reading from stdin causes program to read whatever user types
– User can type control-D to signal end of file
¯ By default, writing to stdout causes program to display information on shell window
26
Redirecting Standard Output: Greater-Than Symbol
Unix Output
Program File
¯ To redirect standard output to fname, put >fname at end of command; e.g.
ls >filelist.txt
will put list of files on file filelist.txt
– If file did not exist, command creates file
– If file did exist, contents replaced
27
Redirecting Standard Input: Less-Than Symbol
Input Unix
File Program
¯ To redirect standard input to come from fname, put <fname at end of command; e.g.
myapp <input.txt
will cause program myapp to read from file input.txt
28
Redirecting Standard Input And Output
Input Unix Output
File Program File
¯ Of course you can redirect both stdin and stdout, e.g.
myapp <input.txt >output.txt
will cause myapp to read from input.txt and write output on output.txt
29
Behaviour of Some Unix Commands
¯ If cat is given no file name argument, it reads from standard input
– cat
will cause whatever the user types (until control-D) to be echoed
– cat >newfile.txt
will cause whatever the user types (until control-D) to be put on newfile.txt
¯ If more is given no file name argument:
– If standard input is a shell window, it complains
– Otherwise, it reads from standard input
– Shows one screenful at a time, as usual
30
Piping Output from Command to Command: Bar Symbol
Unix Unix Unix
Program 1 Program 2 Program 3
¯ We can connect stdout of one command with stdin of another command with “|”
character
¯ Examples:
– ls | more
– If there are a lot of files, shows one screenful at a time
– cat file1.txt file2.txt file3.txt | more
– Concatenates all the files together and shows one screenful at a time
31
Ownership and “Mode” (Access Permission Status)
¯ Every file and directory has
– An owner (userid)
– A “mode” (access permission status)
¯ Generally, you can only create a file on a directory if you are the owner of that directory
– ls -l will tell you about which files you own
¯ By default:
– You can read, write, create, remove files and directories that you own
– You can’t read, write, create, remove files or directories that you don’t own
32
Useful Mode Changing Operations
¯ chmod a+rX fname
– Changes permissions so everyone can read fname
¯ chmod -R a+rX dirname
– Changes permissions so everyone can read every file in dirname directory tree, recur-
sively down to leaf nodes
¯ chmod u+x fname
– Allows you to “execute” fname (treat it as a runnable program)
33
Compiling and Running Programs
¯ Compiling C code
¯ Compiling Java code
¯ Running Java code
34
gcc: Compiling C Code
¯ gcc myapp.c
– Compiles main program myapp.c
– Creates executable file a.out
– Changes mode of a.out so it is executable
¯ gcc -o myapp myapp.c
– Compiles main program myapp.c
– Creates executable file myapp
– Changes mode of myapp so it is executable
– After this, if . is on PATH, issuing command myapp will run that executable file
¯ gcc -c mymodule.c
– Compiles C code in mymodule.c
– Creates object code file mymodule.o
¯ gcc -o myapp.c mymodule.o
– Compiles main program myapp.c
– Links object code in mymodule.o
– Creates executable file myapp, etc.
35
javac: Compiling Java Code
¯ javac MyApp.java
– Compiles Java code in MyApp.java
– Creates MyApp.class
¯ javac -classpath component1:component2:. . . :componentN MyApp.java
For instance:
javac -classpath ~andrews/abbot/abbot.jar:. MyApp.java
– Treats given colon-separated list of components as the classpath
– Each component can be either
– A directory (looks in there for .class files)
– A .jar file
– Note, components separated by colons; no spaces
¯ To avoid having to type in classpath every time, set shell variable CLASSPATH to a path
of that form and export it; e.g.
CLASSPATH=~andrews/abbot/abbot.jar:.
export CLASSPATH
javac MyApp.java
36
java: Running Java Code
¯ java MyApp
– Looks for MyApp.class in CLASSPATH
– Looks for main method in that file
– Runs it
¯ java -classpath classpath MyApp
– Takes that as the classpath
¯ java -jar jarfile MyApp
– Runs main method in indicated class in jarfile
37
bash Shell Scripts
¯ bash shell script = sequence of bash shell commands
¯ Like Windows .bat files
¯ Edit them with normal text editors
38
Contents of Shell Script
¯ Find out where bash lives on the system by typing
which bash
¯ Whatever it says should appear after “#!” on first line of script
¯ Examples:
– If which bash says /usr/local/bin/bash, then first line of shell script should
be
#!/usr/local/bin/bash
– If which bash says /usr/bin/bash, then first line of shell script should be
#!/usr/bin/bash
¯ After first line, just enter normal shell commands into the script
39
Bash Features Useful in Shells
¯ Variables
¯ Arithmetic expressions, inside $(( ... ))
¯ Conditionals, e.g.
if [ $i -eq 5 ]
then
echo Equal to 5
else
echo Not equal to 5
fi
¯ Loops, e.g.
i=0
while [ $i -le 10 ]
do
echo $i
i=$(( i+1 ))
done
¯ Comparison operators: -eq, -ne, -lt, -gt, -le, -ge
40
Permitting and Running Your Shell Script
¯ Change your shell script so it is executable by saying
chmod u+x scriptname
¯ Now run your shell script as if it were an executable file, i.e. by giving the file name as a
command
41
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