Quick UNIX Tutorial

CS4315 A. Berrached::CMS::UHD 1

Quick UNIX Tutorial


Outline

• Getting help while on the system• The shell• Working with files & directories• Wild card characters• Security• I/O redirection• pipes• process and job control commands


Logging in the first time

• Change your passwordpasswd

• To logout logout or exit

Note: all Unix commands are case sensitive


Getting Help from the System• All Unix commands are described online in a

collection of files called “man pages”man command

• For help on some topicman -k keyword

• For more information on using the man pagesman man


General command format

Command -options arguments

• options/flags generally identify some optional capabilities

• some parts of a command are optional. These are indicated in the man pages with [ ]

• case sensitive


The shell• The Unix process that interprets your commands is called

the “shell”• When you login, the login process, after it verifies the

user’s username and password, creates a shell process.• The shell process displays a prompt on the screen and

waits. • When the user enters a command, the shell examines it,

interprets it and either executes it or calls another program to do so.

• After the command is executed, the shell displays the command prompt and waits again.


The shell

• There are several Unix shells• The Bourne shell(sh) and the C shell(csh) are the

most popular. The TC shell (tcsh) is variation of the C shell. Bourne Again Shell (bash) is the default on gator

• To display the shell you’re usingecho$SHELL--> /bin/tcsh

• To change to another shellchsh


Files and Directories• Home directory:

– The actual path of your home directory may be something like: /home/student/username

– Note the forward slashes


Listing contents of a directory

Ls (list files and directories) ls

– The ls command lists the contents of your current working directory.

• > ls Mail courses jets.com News cs4315

g.cc junk proj3 vhdl adsrc ddm ga mail public_html bin exam2.cc misc resch


Listing contents of a directory To generate a detailed listing

ls -l• to display type of file

ls -F• May combine flags

ls -lF To generate listing of a specific directoryls -lF pathnamewhere pathname is the path of intended directory.


Aliases

alias dir = 'ls -lF'


Configuration Files• ls lists all files except those starting with a dot: "."• Generally, files that start with a dot are supposed to

be program configuration files• to list all files and directories in current directory,

including hidden files ls -a


.files• In your home directory there are two hidden files “.login” and ".cshrc"..login: login configuration file.bash_profile: the bash initialization file

• In every directory there are “.” and “..”

“.”: points to the current working directory“..”: points to the parent directory of the

current working directory.


Wildcards• The characters * will match against one or more

characters in a file or directory name. ls proj*

• The character ? Will match against any single character

• [ ]: the brackets enclose a set of characters any one of which may match a single character in that position.e.g cat proj[125]cat proj[1-7]


Wildcards• ~: a tilde at the beginning of a word expands to

the name of your home directory.e.g: ls ~

cat ~/proj1.cc• if you append ~ to a user name, it refers to that

user’s home directory.

e.g: ls ~smithlists all files in home directory of user smith


Making Directories

mkdir (make directory)mkdir name

• creates a subdirectory in current working directory

mkdir somepath/name

• creates a subdirectory in directory somepath


Changing to a different directorycd (change directory)

cd pathname• change current working directory to pathname.

• cd by itself will make your home directory the current working directory

• cd ..: cd to parent of current directory• cd ~ : cd to home directory


Pathnames • pwd (print working directory)

> pwd/home/student/smith


Copying filescp (copy)

cp file1 file2• makes a copy of file1 and calls it file2. File1 and

file2 are both in current working directory.

cp pathname1/file1 pathname2• copies file1 to pathname2e.g cp ~/tutorial/science.txt .


Moving files

mv (move)mv file1 file2

• moves (or renames) file1 to file2• use the -i option to prevent an existing file from

being destroyed mv -i file1 file2

• if file2 already exist, mv will ask if you really want to overwrite it.


Removing files and directories

rm (remove)rm file1 [file2]…

• Use the -i option for interactive remove:

rm -i proj*.*


Removing files and directories

rmdir (remove directory)rmdir path

• will not remove your current working directory• will not remove a directory that is not empty• To remove a directory and any files and

subdirectories it contains use -r (recursively)

rmdir -r pathrmdir -ir path


Displaying the contents of a file on the screen

cat (concatenate)cat myfile

displays the contents of myfile on monitorcat file1 file2 file3

more displays a file on the screen one page at a time. Use space

bar to display to next page.Head -- displays first 10 linestail -- displays last 10 lines


Searching the contents of a file• Searching using moreFor example, to search myfile for the word

science, type more myfile

then type / science

Type n to search for the next occurrence of the word


Searching the contents of a file• Searching using grep> grep music myfile • To ignore upper/lower case distinctions, use the -i

option> grep -i music myfile • To search for a phrase or pattern, you must

enclose it in single quotes. For example to search for the phrase operating systems, type

> grep -i 'operating systems' myfile

> grep -i 'operating systems' *


Searching the contents of a file

Some of the other options of grep are: -v display those lines that do NOT match

-n precede each matching line with the line number

-c print only the total count of matched lines


Other Useful Commands

wc (word count)• To do a word count on myfile, type wc -w myfile

• To find out how many lines the file has, type wc -l myfile

• To do bothwc myfile


Other Useful Commands• wholists on the screen all the users currently logged to

the system• finger usernamelists information about a user• sort takes it is input from the standard input (keyboard)

and sorts the lines in alphabetical order.


Redirecting Input and Output• In general, Unix commands use the standard input

(keyboard) and output (screen).• < : redirect input• > and >> : redirect outputExample:

who > namelistwho >> namelistsort < namelistsort < namelist > newnamelistsort < namelist > namelist


Redirecting Input and Output• Another example: search for the word mysort in

all the c source files in the current directory and write the output to file1.

• grep mysort *.c > file1


Using redirection to concatenate files

• Examples:cat file1 > file2

copies file1 into file2

• To concatenate files:cat file1 file2 > file3

• orcat file2 >> file1


Pipes• A pipe is a way to use the output from one

command as the input to another command without having to create intermediary files.

• Example: want to see who is logged in, and you want the result displayed alphabetically:

who > namelistsort namelist

• Using a pipe:who | sort


Pipes• Example: want to get a count of the users logged

in to the system:who | wc -l

• If you want to display the output of any command one screen at a time: command | more

example:ls -alF | more


Protecting files and directories• The ls -l command display detailed listing of a

file, including its protection mode:

drwxrwxrwx owner size directoryname …..-rwxrwxrwx owner size filename …

• the first character (d or -) indicates whether it is a file or directory name.

• The following 9 character indicate the protection mode.


Protecting files and directoriesrwx rwx rwx

• Each group of three characters describes the access permission: read , write and execute

• the first three settings pertain to the access

permission of the owner of the file or directory, the middle three pertain to the group to which the owner belongs, and the last three pertain to everyone else.


Access rights on files.• r (or -), indicates read permission, that is, the

presence or absence of permission to read and copy the file

w (or -), indicates write permission; that is, the permission to change a file

x (or -), indicates execution permission; that is, the permission to execute a file, where appropriate

example: -rwxrw-r--


Access rights on directories. r: allows users to list files in the directory; w: means that users may delete files from the

directory or move files into it. Never give write permission to others to your

home directory or any of its subdirectories. x: means the right to access files in the directory.

This implies that you may read files in the directory if you have read permission on the individual files.

example: drwxrw-r--


Changing file access permission

chmod (changing protection mode)• Consider each group of three to be a 3-bit number

example: you want to set permission to

rwx r-- --- 111 100 000

7 4 0

chmod 740 filename

chmod codes

Users– u – owner– g – group– o – others– a - all

Access code• r – read• w – write• x- execute


Examples:chmod g+w filenamechmod o-r filenamechmod a-x filename


Process & job control• A process is an executing program with a unique

ID (PID).• To display information about your processes with

their PID and status:ps

• to display a list of all processes on the system with full listing

ps -Af


Process & job control commands• A process may be in the foreground, in the

background, or be suspended. In general the shell does not return the UNIX prompt until the current process has finished executing.

• To run a program in the background, append a & at the end of the command

prog1 &[1] 6259

• system returns the job number and PID


Process & job control commands• To suspend a running process

CTRL Z• example: % prog

CTRL Z• To background a running processCTRL Zbg

• To bring a process to forgroundfg %job


Process & job control commands• to kill a background process

kill PID• to suspend a running background process

stop PID


Process & job control commands• Background process can not use the standard

I/O. ==> Need to redirect I/O

e.g: grep mysort *.c &

output will be lost

grep mysort *.c > file1 &

Kill Command• kill –s STOP PID --- suspend• kill –s CONT PID --- resume• kill –s TERM PID --- terminate



Compiling C programs

cc [options] file …• by the default, the resulting executable is a.out

cc prog.c

cc -o prog prog.c• names the resulting executable prog instead of a.out

• Compile a C++ programg++ prog.cpp


Editing files

Available editors:• vi • emacs• picoCheck references on web

vi commandsa – appendi – insertx – eraseEsc – return to command modeShift : - enter file command modew – writeq – quitw! – force writeq! – force quit


File transfer• WS_FTP - a GUI ftp program• ftp on command prompt

– ftp gator.uhd.edu– After login:

• put – transfer a single file from the current folder on local machine to the current directory on Gator

• mput – upload multiple files• get – transfer a single file from the current directory on Gator

to the local machine• mget – download multiple files• cd – change the current directory on Gator• lcd – change the current folder on the local machine• bye – quit ftp



Example: Writing a C program on Unix

• Write a program that counts the number of non white-space characters in a text file. Program takes as command argument the name of the input file and displays the output on the standard output.


// Character Count: Basic Algorithm#include <stdio.h>#define BLANK ' '#define NEWLINE '\n'int main(int argc, char *argv[]){ FILE *infile;

char c;int char_count=0;// count the number of charecters in infilewhile ( (c = getc(infile)) != EOF)

if ((c != BLANK) && (c != NEWLINE) )++char_count;

printf("%d characters\n", char_count);return 0;

}


Testing the # of command arguments

if (argc != 2){

fprintf(stderr, " %s: expects 1 argument but was given %d\n", argv[0], argc-1);fprintf(stderr, "Usage: %s inputfile \n", argv[0]);exit(1);

}

int printf( char *format, arg1, arg2, ….)

int fprintf( FILE * stream, char *format, arg1, arg2, ….)

Format specifiers used by printf• %c – character• %[n]s – string. n is the width of the field• %[n]d – integer• %[n.m] – floating point number

– n – the width of the field– m – the number of digits in the fractional part



Opening input fileif ( (infile = fopen(argv[1], "r")) == NULL){

fprintf(stderr,"%s: cannot open %s \n", argv[0], argv[1]);exit(1);

}

File *fopen(char *filename, char *mode);


file modes"r" : open text file for reading

" w" : for writing

"a" : for appending

"r+" : reading and writing

"w+": for reading and writing (discard existing file)

"a+": open text file for appending


Count and return # of chars

// count the number of charecters in infilewhile ( (c = getc(infile)) != EOF)

if ((c != BLANK) && (c != NEWLINE) )++char_count;

printf(" %d characters\n ", char_count);return 0;

}


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