linux commandz class 5

8/3/2019 Linux Commandz Class 5

1/26

File System

BASIC DEFINITIONS

A file is a collection of information stored on a computer system.

A directory is a special file that contains the names of other files and/orsubdirectories. Files can be organized efficiently with the use of directories. Adirectory can be used to group related files and subdirectories together.

A subdirectory is a directory within a directory.

FILE ORGANIZATION

Files can be organized into a hierarchy of directories. A typical UNIX fileorganization structure resembles an upside-down tree.


2/26

In this inverted-tree structure, any file can be accessed from anywhere in the tree.

DEFINITIONS

The home directory is a directory assigned to a user. Usually, all files created bythe user are within this directory.

The current working directory (.) is the directory in which you are currentlylocated. After you login, your current working directory is your home directory.

The parent directory (..) of a file is the directory which directly encloses the file.For example:

charles is the parent directory of .login, history, calculator, and calculator.c

The root directory (/) is the directory that encloses ALL files and directories;therefore, it has no parent directory.

PATHNAMES

Because of this hierarchy of directories, it is sometimes necessary to specify thepath to a file or directory.

Example: /home/1/charles/history/week1.notes and history/week1.notes are bothparameters to the week1.notes file

Note that / is used to separate directory names.

Absolute Pathname: A pathname that starts with / (the root). Since the path alwaysstarts at the root, it is correct regardless of what the current working directory is.

Relative Pathname: A path that starts from the current working directory. Any

pathname that does not start with / is taken to be a relative pathname.

Example: If the current working directory is /home/1/charles

then the absolute and relative pathnames to week1.notes respectively are

/home/1/charles/history/week1.notes and history/week1.notes


3/26

cal - displays a calendar

cal [[ month ] year]

Cal displays a simple calendar. If arguments are not specified, the current month

is displayed.

A single parameter specifies the year (1 - 9999) to be displayed; note the yearmust be fully specified: ``cal 89 '' will notdisplay a calendar for 1989. Twoparameters denote the month (1 - 12) and year. If no parameters are specified, thecurrent month's calendar is displayed.

Ex:

Code:

# cal 3 2001

______March 2001

Su Mo Tu We Th Fr Sa

____________01 02 03

04 05 06 07 08 09 10

11 12 13 14 15 16 17

18 19 20 21 22 23 24

25 26 27 28 29 30 31

date - print or set the system date and time

date

Display the current time .

Ex:

$ date

Sun oct 16 16:15:21 IST 2011

$ date +%m

08


4/26

$date +%h

Aug

$date +%h %m

Aug 08

Options:

d- The day of the month (1 to 31)y- The last two digits of the year.H,M and S The hour, minute and seconds respectively.

D- The date in format mm/dd/yy

T- The time in the format hh:mm:ss

who - show who is logged on

who options

H, --headingprint line of column headings

-u, --userslist users logged in

ex:

$ who

root console sep 1 07:10 (:0)kumar pts/10 Aug 1 08:56 (pc123.datastage.com)

$ who am i

kumar pts/10 Aug 1 08:56 (pc123.datastage.com)


5/26

passwd

Allows the user to change your account password. Your password should be at

least four characters in length, up to a maximum of eight. It is also desirable to

include numbers and mixed case characters within the password for additionalsecurity. Develop a habit of changing your password on a regular basis

cd path

The change directory command moves the user from the current working

directory to the directory specified. Ifpath is defined as a simple name such as

docs, then docs is located directly below the current directory and the user ismoved into it. The command cd, by itself on a line, returns the user to the login

directory. Examples of uses ofcdare

cd docs : Move down to the directory named docs.

cd .. : Move up to the parent directory of the current directory.

cd ../data : Move up to the parent directory of the current directory, then down to

the directory named

data.

cd /usr/local/bin: Move to the explicit directory location.

mkdir directory

This command is used to create a new directory within the current directory.

pwd

Thepwdcommand (print working directory) allows you to determine the path

name of the directory in which you are presently working.


6/26

rmdir directory

The rmdir(remove directory) command is used to delete a directory. You can

only delete an empty directory.

cp file1 file2

The cp (copy) command takes the contents of one file (file1 ) and duplicates it

to another file (file2 ).cp file1 file2 file3 progs Destination should be a folder.

cp file* progs Copies all the files starts with file to progs

cp i file1 file2

cp R progs newprogs

this command behaves recursively to copy an entire directory structure progs to

newprogs.

The copying depends on the existence of the destination directory.

If newprogs exists progs becomes a subdirectory under newprogs.

If newprogs doesnt exist, cp creates it along with the associated subdirectories.

mv file1 file2

Move (mv) renames and moves files. If file2 already exists, it is deleted before

file1 is renamed

mv file1 file2 file3 progs The last one should be directory.

mv progs progs1 It depends on the destination directory exists or not.


7/26

rm filename

The rm (remove) command is used to delete a file.

rm file 1 file2 file 3

rm progs/file4 progs/file4rm *

rm i file 1 file2 file3

i is for interaction.

rm r * very dangerous and removes all the files in subdirectories also.

rm rf * very very dangerous because all the files will gone though we donthave permissions to do that.

ls

Lists the contents of the current directory. ls has many parameters.

ls -a Lists all files, including invisible files (files

with a leading dot (.)).

ls A --almost-alldo not list implied . and ..

ls -FPlaces a slash (/) after directory files and an

asterisk (*) after executable files, and places

an at-sign (@) after symbolic links.

ls -R Recursively lists all files, including those in

sub-directories from the current sub-directory

to all sub-directories below.

ls -r, --reversereverse order while sorting


8/26

ls -d, --directorylist directory entries instead of contents

ls -l Lists all visible files and some attributes.

$ ls l

-rw-r- -r- - 1 kumar dstage 1954 may 11 13:45 file1

drwxr-xr-x 2 kumar dstage 512 june 15 15:45 progs1

chmod

Allows the owner of a file or directory to change the access permissions.

Use of pneumonics is preferred over the octal numbers as pneumonics are

additive and subtractive, octal numbers are absolute and may change

something that you didn't want to.

chmod go-rwx filename

chmod 600 filename Makes a file private.

chmod a+r filename

chmod 644 filename Makes a file public in read mode.

chmod go-rwx,u-wx+r filename

chmod 400 filename Makes a file private and protects it from

accidental change/deletion.

chmod u+x filename

chmod 700 filename Makes a file executable by the owner. This

file can then be executed by simply entering

its name.

chmod a+rx dirname

chmod 755 dirname Makes a directory public in read mode. Note:


9/26

Directories must be "executable" in order to

be searched.

Cat:It is used to display the contents of a file on the terminal.

$cat dept.lst

01 | accounts | 6213

02 | progs | 5423

03 | marketing | 6521

04 | personnel | 2365

05 | sales |1006$cat file1 file2

The contents of the second file are shown immediately after the first file without

any header information.

$cat n file1

The n option numbers lines.

We can also use cat to create a file.

$cat > foo

This is the first which is been created so far.

[ctrl-d]

$_

This means we entered some text into the file.

If we do

$cat foo

This is the first which is been created so far.

Cat is used for both creating a file as well as to enter some input into file


10/26

wc : Counting lines, Words and Characters

$ cat infile

I am the wc command

I count characters, words and linesWith options I can also make a selective count

$wc infile

3 20 103

A line is any group of characters not containing a new line.

A word is a group of characters not containing a space, tab or newline.

A Character is the smallest unit of information, and includes a space, tab and

newline$ wc l infile

3 infile

$ wc w infile

20 infile

$ wc c infile

103 infile

$ wc file1 file2 file3

5 16 45 file1

8 24 75 file2

7 28 86 file3

cmp: Comparing two files

$ cmp file1 file2

file1 file2 differ: char 9, line1


11/26

The two files are compared byte by byte and the location of the first mismatch will

be displayed on the screen. By default, cmp doesnt bother about the possible

subsequent mismatches.

If the two files are identical then it wont displays any message, but simply returns

the prompt.

Comm.: What is Common?

It requires two sorted files and lists the differing entries in different columns.

$cat file1

c.k. Shuklachanchal singhvi

s.n. dasgupta

sumit chakrobarty

$ cat file2

anil aggarwal

barun sengupta

c.k. shukla

lalit chowdury

s.n. dasgupta

Both files are sorted and have some differences.

When you run the comm, it displays a three-columnar output.


12/26

$ comm. file1 file2

anil aggarwal

barun sengupta

c.k. shuklachanchal singhvi

lalit chowdury

s.n.dasgupta

sumit chakrobarty

diff: Converting one file to another file

diff is the third command that can be used to display file differences. Unlike its

fellow members cmp and comm, it also tells you which lines in file one have to be

changed to make the two files identical.

$ diff file1 file2

0a1,2

> anil aggarwal

> barun sengupta

2c4

< chanchal singhvi

--

>lalit chowdury

4d5

< sumit chakrabarty

Diff uses certain symbols and instructions to indicate the changes that are required

to make two file identical.


13/26

head: Displaying the beginning of the file

$ head n 3 dept.lst


02 | progs | 542303 | marketing | 6521

It displays the first 3 lines of the file dept.lst

If we give only

$ head emp.lst

It displays first 10 lines of a file by default.

tail: Displaying the end of a file

$ tail n 3 dept.lst



05 | sales |1006

It displays the last 3 lines of the file dept.lst

If we give only

$tail dept.lst

By default, it gives last 10 lines of the file.


14/26

cut : Slitting a file vertically

$ cut c 5-10,13-16 dept.lst

accounts 6213

progs 5423marketing 6521

personnel 2365

sales 1006

If I use

cut c -3,6-9,11- dept.lst

then, It displays the first 3 columns and 6 to 9 columns an then 11th

column to tilllast.

cut d | f 2,3 dept.lst

accounts | 6213

progs | 5423

marketing | 6521

personnel | 2365

sales | 1006

If we want to know all the users who logged in then,

$ who | cut d f1

Paste: Pasting Files

$ paste emp1.lst emp2.lst

It means displays the files side by side

If we want to display the files side by side but with a delimiter then we need to

specify the delimiter.

$ paste d | emp1.lst emp2.lst


15/26

sort : Ordering a file

It is used to sort the content of a file.

$ sort dept.lst

The contents of the file are sorted.If we want to sort the contents based on a column then we need to specify the

column, as specified below.

$sort t | -k 3 dept.lst

05 | sales |1006


02 | progs | 5423

01 | accounts | 621303 | marketing | 6521

If we want to sort them in the reverse order then we need use the option -r

$sort t | -r -k 3 dept.lst



02 | progs | 5423


05 | sales |1006

If we want to sort the data based on two columns one after the other then we need

to specify both the columns.

$ sort t | k 3,3 k 2,2 dept.lst

If we want to sort a numeric file then we need to give the option n .

$sort n numfile


19/26

grep : Searching For a Pattern

If we want to search for a particular pattern then we need to give the pattern and

the file name.

If we want to know the log in details of a particular user then we need to give the

command

$ who | grep kumar

If we want to search in more than one file then we need to give the filenames as

follows.


20/26

If we are searching for a particular pattern which contains more than one word,

then we need to give the pattern in quotes.

$ grep jai sharma emp.lst

Ignoring Case (-i):

If we want to make the command case insensitive then we need to give the i

option.

$ grep i agarwal emp.lst

3546 | sudhir Agarwal | executive | personnel | 06/07/47 | 7500

Deleting Lines (-v) :

$ grep v director emp.lst > otherlist

$ wc l otherlist

11 otherlist

Displaying Line Numbers (-n):If we want to display the line number along with the lines then we need to use the

option -n

$ grep n marketing emp.lst

3:5678 | sumit chakrobarty | d.g.m | marketing | 19/04/43|6000

.

.

15:0110| v.k.agarwal | g.m. | marketing | 31/12/40 | 9000

Counting Line Containing Pattern (-c):

$ grep c director emp.lst

4


21/26

Displaying Files:

$ grep l manager *.lst

design.lst

emp.lstemp1.lst

emp2.lst

Matching Multiple Patterns (-e):

If we want to search for multiple patterns then we need to give the e option.

$ grep e Agarwal -e aggarwal -e agrawal emp.lst

Taking Patterns from a File (-f):We can store the pattern in a file and then we can give it as the input to the

command.

$ grep f pattern.lst emp.lst

Specifying Pattern Locations (^ and $):

^ - For matching at the beginning of a line.

$ - For matching at the end of a line.

$ grep ^2 emp.lst

It will display the lines which dstarts with 2 .

$ grep 7$ emp.lst

It will display the lines where the last 4 characters line between 7000 and 7999

sed : The Stream Editor

If we want to display the first 3 lines of a file then we should use


22/26

Generally, we will be using the p (print) command to display the lines. We should

use n option along with p option to suppress the duplication of lines.

To print only the last line we should use

We can also select lines from anywhere.

Selecting multiple group of lines

sed -n 1,2p 7,9p $p emp.lst

Negative Action(!):

If we dont want to print the lines from 3rd to last line then we need to use

$ sed n 3,$!p emp.lst

We can use multiple instructions in a single command as follows.

The following command will display lines 1,2 and 7-9 and then the last line.

sed n e 1,2p, -e 7,9p e $p emp.lst

we can also put these file numbers in a file and we can pass this file as the pattern.

$ cat instr.lst

1,2p

7,9p

$p

sed n f instr.lst emp.lst


23/26

We can use sed for the pattern matching also.

$ sed n /director/p emp.lst

It will display all the lines which contains the pattern director in them.

We can also use like this.$ sed n /[aA]ggarwal/p emp.lst

It will display the lines which contains either Aggarwal or aggarwal.

$ sed n /50..$/p emp.lst

Then it displays the lines which contains 50 at 6th and 7th characters from last.

Writing Selected Lines into a File(w):

Sed n /director/w dlist emp.lstThen it will write the lines which contains the pattern director in them into the

file dlist.

$ sed n 1,500w foo1 501,$w foo2 foo.12

Then it will write the first 500 lines of the foo.12 file into foo1 and the remaining

lines into foo2.

Substitution(s):

$ sed s/|/:/ emp.lst

Then 1st occurrence of | in every line will be replaced by :

If we want to make this change to the entire line, wherever it appears in the line

then we need to use the option g(global).

$sed s/|/:/g emp.lst

Then the character | will be replaced by : in the entire file wherever it appears.

$sed 1,3s/|/:/g emp.lst

Only for the first 3 lines.


24/26

Basic Shell Scripting:

Interaction with the user:

The output will be


25/26

awk: An Advance Filter:

Simple awk Filtering:

If we are searching for a pattern in a file the we can give the command as follows.

And it is equivalent to the following commands.

awk /director/ emp.lst

awk /director/ { print $0 }

Splitting A Line into Fields:

If we want to display only few fields in a file, then we can use the following

command by specifying the delimiter.

The above command prints only the fields 2nd, 3rd, 4th and 6th fields only.

We can also specify the from which line to which line we need to display by using

the NR value.

In the below example, It will display the NR value, 2nd ,3rd and 6th fields of a file.


26/26

linux commandz class 5

Documents