file system in unix

Files and Directories in UNIX

The first file in UNIX file system is “root” or “/”

... A lice abuzneid

a.doc c.doc

D ocum ents

inbox sendm ail

personal M em os

sbenayed ali m ahm ood

/ (R OO T)

Files and Directories in UNIX (continue.)

Home directory (could be named differently) has subdirectory per user called “User Home Directory”

Directories can have more subdirectory and files A file or a directory can be referred to by

Relative path name [a.doc if you are at Documents] Absolute path name

[/home/abuzneid/UNIX/Documents/a.doc}\] File and directory names are case sensitive

To display working directory$ pwd

/home/abuzneid/UNIX

$ ls -l

total 8

drwxr-xr-x 2 abuzneid 534 512 Oct 8 13:40 Documents

drwxr-xr-x 2 abuzneid 534 512 Oct 8 13:43 mail

drwxr-xr-x 2 abuzneid 534 512 Oct 8 13:53 memos

drwxr-xr-x 2 abuzneid 534 512 Oct 8 13:53 personal

$ cd Documents

/home/abuzneid/UNIX/Documents

cd command to change directory

/home/abuzneid/UNIX

$ ls -l

total 8

$ cd Documents

$ cd ..

/home/abuzneid/UNIX

$ cd /

$ cd /home/abuzneid/UNIX/Documents

$ cd ../..

/home/abuzneid

List Files ls command is used to list files and directories ls –l displays more information about every file

and directory file type

d for directory - for file b, c, p for special file

access made for the owner, group and others number of links owner of the file Size last modification file name

List Files (continue.)

a.doc c.doc

$ ls -l

total 4

-rw-r--r-- 1 abuzneid 534 14 Oct 8 13:37 a.doc

-rw-r--r-- 1 abuzneid 534 14 Oct 8 13:38 c.doc

/home/abuneid

$ ls UNIX

Documents mail memos personal

List Files (continue.)

$ ls -a

. .. Documents mail Memos personal

Creating a Directory: the mkdir command

mkdir command$ pwd

/home/abuzneid/UNIX

$ mkdir test

Documents mail Memos personal test

$ cd test

/home/abuzneid/UNIX/test

Copying file from directory to another

$ cp UNIX/personal/p1 UNIX/Documents/p11

$ ls UNIX/Documents

a.doc c.doc p11

$ cp UNIX/personal/p1 UNIX/Documents

$ ls UNIX/Documents

a.doc c.doc p1 p11

$ cd UNIX/personal

/home/abuzneid/UNIX/personal

$ cp p1 p2 /home/abuzneid/UNIX/mail

Moving Files between Directories

$ cd /home/abuzneid/UNIX/personal

$ ls -l

total 4

-rw-r--r-- 1 abuzneid 534 11 Oct 10 21:46 p1

$ mv p1 p2 /home/abuzneid/UNIX/Memos

$ cd /home/abuzneid/UNIX/Memos

Rename File or Directory

mv is used to rename a file of a directory$ ls -l

total 14

drwxr-xr-x 2 abuzneid 534 512 Oct 10 21:54 Memos

drwxr-xr-x 2 abuzneid 534 512 Oct 8 23:42 TEST

drwxr-xr-x 2 abuzneid 534 512 Oct 10 21:39 test

$ mv Memos memos

Rename File or Directory (continue.)

Memos renamed to

$ ls -l

total 12

Removing a directory: the rmdir command

To remove a directory: rmdir <directory name> if the directory is

empty rm –r <directory name> if it’s not empty

Removing a directory: the rmdir command (continue.)

$ rmdir /home/abuzneid/UNIX/memos

rmdir: directory "/home/abuzneid/UNIX/memos": Directory not empty

ALL SUBDIRECTORIES AND FILES IN memos MUST BE DELETED FIRST

$ cd /home/abuzneid/UNIX/memos

$ ls -l

total 4

$ rm *

$ cd ..

$ rmdir memos

$ ls -l

total 10

Linking Files: the ln command

To have two copies of any file, you can use: cp to copy it to another file, or ln to link the file to another file

The disadvantages of cp Consumes twice as much disk space Both files always has to be changed if any of them is updated

to keep them identical Number of links to a file is, normally 1 for non-linked,

non-directory files More than one link to a file is possible Most often, ln is used to link files between directories

Linking Files: the ln command (continue.) There is two types of links

Hard disk Soft link

ln <form to> ln <–s from to>

“to” can be file or directory “to” can be file or directory

“to” and “from” must resides on the same file system

“to” and “from” may resides on different file system

“to” and “from” will have the same size

“to” will have a size of link (pointer) to “from”

If “to” is deleted “from” will work fine and vice versa

If “from” is deleted, “to” will not work

Linking Files: the ln command (continue.)

$ cat aaa

Bridgeport

Massashusets

New Hampshire

Vermont

$ ls -l

total 12

-rw-r--r-- 1 abuzneid 534 46 Oct 10 23:14 aaa

-rw-r--r-- 1 abuzneid 534 34 Oct 10 23:12 bbb

$ ln aaa bbb

$ ls -l

total 14

-rw-r--r-- 2 abuzneid 534 46 Oct 10 23:14 aaa

$ cat bbb

Bridgeport

Massashusets

New Hampshire

Vermont

$ echo one more line >> aaa

$ cat aaa

Bridgeport

Massashusets

New Hampshire

Vermont

one more line

$ cat bbb

Bridgeport

Massashusets

New Hampshire

Vermont

one more line

$ rm aaa

$ cat bbb

Bridgeport

Massashusets

New Hampshire

Vermont

one more line

$ cp bbb ccc

$ ln -s ccc ddd

$ ls -l

total 16

-rw-r--r-- 1 abuzneid 534 60 Oct 10 23:25 ccc

lrwxrwxrwx 1 abuzneid 534 3 Oct 10 23:26 ddd -> ccc

$ rm ccc

$ cat ddd

cat: cannot open ddd

File Name Substitution

$ lsbbb ddd Documents mail personal TEST

$ echo *Documents TEST bbb ddd mail personal test

$ echo *.**.*

$ echo a*a*

$ echo m*mail

$ echo *a*mail personal

•The asterisk ”*”: substitutes zero or more characters

File Name Substitution (continue.)

“?” matches single character

bbb ddd Documents mail personal TEST test

$ echo ???

bbb ddd

File Name Substitution (continue.)

Matching a single character using square brackets []

[abc] matches one letter [!a-z] matches any character except a lower

case letter *[!X] matches any file that doesn't end with

the upper case X

Standard Input/Output

Standard input is the terminal (keyboard) Standard output is the terminal (display)

commandstandard input standard output

Standard Input/Output (continue.)

If a sort command is executed without a file name argument, then the command will take its input from standard input

whoskan tty01 Jan 07 07:56wiem tty52 Jan 07 06:15samir tty03 Jan 07 09:26

Example:

$ sort

sortskanwiemsamir

skanwiemsamir

Output Redirection

Output directed to a file instead of standard output command > ofile directs output to the file ofile command >> ofile appends output to the file

ofile > ofile creates an empty file

“ofile”

Output Redirection (continue.)

Example:$ who > users

$ cat users

bgeorge pts/16 Oct 5 15:01 (216.87.102.204)

abakshi pts/7 Oct 10 22:56 (216.87.102.210)

abuzneid pts/9 Oct 10 19:29 (avicenna.102.87.216.in-addr.arpa)

xiafeng pts/10 Oct 10 23:16 (Shiva-RAS-Pool-13.uhmc.sunysb.edu)

$ echo add one more line >> users

$ cat users

bgeorge pts/16 Oct 5 15:01 (216.87.102.204)

abakshi pts/7 Oct 10 22:56 (216.87.102.210)

abuzneid pts/9 Oct 10 19:29 (avicenna.102.87.216.in-addr.arpa)

add one more line

$ > users

$ cat users

Input Redirection

Input of a file is redirected from a file command < infile get the input from the file infile

Example:

$ who > users

$ wc -l users

15 users

$ wc -l < users

Connects the output of one command to the input of another command

Example:

$ who | wc -l

$ ls | wc -l

Pipes (continue.)

wc -l 5who

Filters

Any program that can take input from standard input, perform some operation on that input, and write the results to standard output

Example: cat and sort are filters

Standard Errors

Terminal is the standard error In most cases, you never know the

difference between standard output and standard error command 2> efile directs the error to the file

Standard Errors (continue.)

Examples:$ ls n*

n*: No such file or directory

$ ls n* > foo

n*: No such file or directory

$ ls 2> foo

bbb Documents mail TEST users

ddd foo personal test

$ cat foo

References UNIX SHELLS BY EXAMPLE BY ELLIE

QUIGLEY UNIX FOR PROGRAMMERS AND

USERS BY G. GLASS AND K ABLES UNIX SHELL PROGRAMMING BY S.

KOCHAN AND P. WOOD

file system in unix

cd test

cd command

cd documents

ls ltotal

cd homeabuzneidunixmemos

cd unixpersonal

cd homeabuzneidunixdocuments

cd homeabuzneidunixpersonal

Documents

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