COMP1070/2002/lec4/H.Melikian COMP1070 Lecture #5 Files and directories in UNIX Various types of...

COMP1070/2002/lec4/H.Melikian

COMP1070Lecture #5

Files and directories in UNIXVarious types of filesFile attributesNotion of pathnameCommands manipulating files and directories


Files and Deroctories

File related operations create, read, write, modify and executeFile – sequence of bytes.Directories , network cards, disk drives, a

keyboard, a printer also are filesTypes of files simple./ ordinary directory symbolic(soft) links special files(device) named Pipe (FIFO)


Directory

File names 14 – 256 characters (System v )Extensions - name.extension like prog.c, letter.doc, pine.exe A Directory contains the names of other files

and/or directories ( subdirectories)- folder


File system Organization

The UNIX file system is structured hierarchically ( upside down treelike). It starts at root directory ( / ) and goes down .

When you login the unix puts you in a specidic dir, called home or login directory ( specified in c shell by ~ )

Pwd – present working directory or current directory


Pathnames

Files are specified by pathname. There are three ways to specify pathname1. Starting with the root directory( absolute)2. Starting with the pwd3. Starting users home directory (relative )Standard directories and filesRoot ( /), /bin ( binary executables), /dev, /etc (for

systemadmin) /lib, /tmp, /users, /usr ( UNIX utilities,

manuals) /var ( mails ..) /etc/passwd file contains one

line foeevery user.


Navigating the file systemCommand to browse file system:

cd[directory], ls[option][pathname-list], pwd

Hidden files ., .., addressbook, .cshrc, .login, .pinerc, .profile . . .


Creating and removing files (Directories)

You can create file using various editors containing

plane text or specific application tools (compilers)to create

nontext file. To create directory we use mkdir commandmkdir [option]dirnameTo remove directory we use rmdir commandrmdir[options]dirnameOptions: –r and -p


Determining file AttributesTtype % ls -l (l for long listing!)You will see long listing of

files with various options.


Access rights on files

r (or -), indicates read permission (or otherwise), that is, the presence or absence of permission to read and copy the file

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

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

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; x means the right to access files in the directory. This implies

that you may read files in the directory provided you have read permission on the individual files.


Changing access rightschmod (changing a file mode)Only the owner of a file can use chmod to change the permissionsof a file. The options of chmod are as follows Symbol Meaningu user , g group, o other a allr read, w write (and delete) x execute (and access dir) +add permission - take away permissionFor example, to remove read write and execute permissions on thefile biglist for the group and others, type % chmod go-rwx letter.txt This will leave the other permissions unaffected. To give read and write permissions on the file letter.txt to all, % chmod a+rw letter.txt


Default File Access Privileges

Octal representation of file privileges r – 4, w –2 , x – 1 wre = 4+2+1=7 or Example: % chmode 755 letter.txtumask[ mask]- sets access permission bit on newly

created files and directories.File access permition = 777 – mask where mask is octal number Commonly use mask is 022Hence default access permission is set to 755To display the current value of mask% unmask022%


Copying Files

cp (copy)

% cp file1 file2

is the command which makes a copy of file1 in the current

working directory and calls it file2 What we are going to do

now, is to take a file stored in an open access area of the file

system, and use the cp command to copy it to your unixstuff

directory. First, cd to your unixstuff directory.

% cd ~/unixstuff


Moving files

mv (move)mv file1 file2 moves (or renames) file1 to file2 To move a file from one place to another, use the mv command.This has the effect of moving rather than copying the file, so you end up with only one file rather than two. It can also be used torename a file, by "moving" the file to the same directory, butgiving it a different name. We are now going to move the filescience.bak to your backup directory. First, change directories toyour unixstuff directory (can you remember how?). Then, insidethe unixstuff directory, type% mv science.bak backups/.Type ls and ls backups to see if it has worked.


Removing files and directories

rm (remove),rmdir (remove directory)To delete (remove) a file, use the rm command. As an example,we are going to create a copy of the science.txt file then delete it. Inside your unixstuff directory, type% cp science.txt tempfile.txt% ls (to check if it has created the file)% rm tempfile.txt % ls (to check if it has deleted the file) You can use the rmdir command to remove a directory (make sureit is empty first). Try to remove the backups directory. You willnot be able to since UNIX will not let you remove a non-emptydirectory.


Simple searching using less

Using less, you can search though a text file for a keyword

(pattern). For example, to search through science.txt for the word

science, type

% less science.txt

then, still in less (i.e. don't press q to quit), type a slash followed by

the word to search

/science

As you can see, less finds and highlights the keyword. Type n to

search for the next occurrence of the word.


Simple searching using grep

grep is one of many standard UNIX utilities. It searches files for specified words or

patterns. First clear the screen, then type % grep science science.txt As you can see, grep has printed out each line containing the word science% grep Science science.txt The grep command is "case sensitive"; it distinguishes between Science andscience. To ignore upper/lower case distinctions, use the -i option, i.e. type % grep -i science science.txt To search for a phrase or pattern, you must enclose it in single quotes (theapostrophe symbol). For example to search for spinning top, type % grep -i 'spinning top' science.txt 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 % grep -ivc science science.txt


Summarycp file1 file2 copy file1 and call it file2

mv file1 file2 move or rename file1 to file2

rm file remove a file

rmdir directory remove a directory

cat file display a file

more file display a file a page at a time

head file display the first few lines of a file

tail file display the last few lines of a file

grep 'keyword' file search a file for keywords

wc file count number of lines/words/characters in file


HW #21. Write a short description of the following UNIX

commands using man utility then send it to me.

chmod , grep, , rm, cat.

2. Use script program on UNIX, to write your unix

season into the file called typrscript( by default).

You working season must include implementation of all the

listed command with their most common options

Assigned 09/16/02 Due 09/23/02 by midnight 12:00 (p.m.)

PS. To submit you have to use the fallowing command % mail melikian< typescript


A typical UNIX file system structure

COMP1070/2002/lec4/H.Melikian COMP1070 Lecture #5 Files and directories in UNIX Various types of...

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