EX.NO:1b UNIX COMMANDS

(I)GENERAL PURPOSE COMMANDS

  1. date

The date command is used to display the current date with day of week, month, time and the year.

Syntax: $ date

             $date  +[%format]

Example:

a) $ date

     Fri Mar  4 09:13:05 IST 2011

b) $ date +%m –  Displays only the current month (1..12)

     03

c) $ date +%M – Displays only the minutes (00…59)

    18

d) $ date +%d – Displays only the day of month (1…31)

     04

e) $ date +%D – Displays the date in mm/dd/yy format

     03/04/11

f) $ date +%h – Displays current abbreviated month name

    Mar

g) $ date +%H – Displays the hour (00…23)

     09

h) $ date +%Y – Displays the year

     2011

i) $ date + %y – Displays the last two digits of the year

   11

  1. cal

The cal command displays the specified month or year calendar

Syntax : $ cal [options]

              $cal [month][year]

i)$ cal – Displays the current month calendar

ii) cal -3 – Displays the prev/current/next month calendar.

iii)$ cal 06 2011 – Displays the calendar for June 2011

iv) $ cal 2011 –Displays the calendar for the entire year 2011 

  1. bc

Unix offers an online calculator and it can be invoked by the bc command.

Syntax:  $ bc

When u type bc at the $ prompt, you are in the calculator mode and the $ prompt disappears. Type the input and press enter and observe the output. To quit calculator mode press ctrl d.

Example:

$ bc

3 + 4 * 5

23

  1. who

The who command displays the details about all the users who have currently logged into the system.

Syntax: $ who

Example : $ who

root            tty1          2011-03-04 08:30

  1. who am i

The who am I command displays the details about the current user.

Syntax : who am i

Example : $ who am i

punitha   pts/0    2011-03-04 09:04 (10.0.5.32)

  1. finger

The finger command displays the details about all the users who have currently logged into the system

Syntax: $ finger

Example : $finger

Login          Name         Tty      Idle    Login  Time       Office           Office Phone

punitha       punitha       pts/0             Mar   4 09:04   (10.0.5.32)

  1. echo

The echo command is used to display the specified text on the screen

Syntax: $ echo “some text”

Example : $ echo “Good day”

Good day

(II)FILE RELATED COMMANDS

  • cat

a)The cat command is used to create a file.

Syntax: $ cat > filename

Example : $ cat > sample

welcome to

unix lab

[press ctrl + d]

b)The cat command is used to view the contents of the specified file.

Syntax: $ cat filename

Example : $ cat sample

welcome to

unix lab

c)The cat command is used to append contents to an existing file.

Syntax: $ cat >> filename

Example: $ cat >> sample

This is our first program

[press ctrl + d]

$ cat sample

welcome to

unix lab

This is our first program

  1. cp

a)The cp command is used to copy the contents of one file to another file.

Syntax: $ cp sourcefile destinationfile

Example : $ cp sample test

$ cat test

welcome to

unix lab

This is our first program

b)The cp command is also used to copy a file to another directory.

Syntax: $ cp source_file destination_directory

Example : $ cp sample dir1

  1. mv

a)The mv command is used to remove a file from its current location and copy it to a new location.

Syntax: $ mv source_file destination_directory

Example: $ mv test dir1

b)The mv command is also used to rename a file.

Syntax: $ mv old_filename new_filename

Example: $ mv test test1

  1. ln

The ln command is used to establish an additional link for the same file.

Any modification made in the additional file or in the original file is reflected in both of them.

Syntax: $ ln existing_file new_file

Example : $ ln sample sample1

 

  1. rm

The rm command is used to remove the specified file.

Syntax: $ rm filename

Example: $ rm sample

  1. cmp

The cmp command is used to compare two files. It tells u whether two files differ and if they differ, it reports the position in the file where the first difference occurs.

Syntax : $ cmp filename1 filename2

Example : $ cat file1

welcome to

unix lab

$ cat file2

welcome to

linux lab

$ cmp file1 file2

file1 file2 differ : byte 12, line 2

  1. comm

The comm command compares two sorted files line by line.

It produces a three-column output.  Column one contains lines unique to file1, column two contains lines unique to file2, and column three contains lines common to both files.

Syntax: $ comm [options] filename1 filename2

Following are the different options.

a) -1 suppress lines unique to file1

b) -2 suppress lines unique to file2

c) -3 suppress lines that appear in both files

Example : $ cat  file3

one

three

$ cat  file5

one

five

i)$ comm file3 file5

one

five

three

ii)$ comm -1 file3 file5

one

five

iii)$ comm -2 file3 file5

one

three

iv)$ comm -3 file3 file5

five

three

  1. paste

The paste command joins files together line by line.

Syntax : $ paste filename1 filename2

Example : $ cat countries

India

Pakistan

Australia

$ cat capitals

Newdelhi

Islamabad

Canberra

$ paste countries capitals

India              Newdelhi

Pakistan        Islamabad

Australia       Canberra

  1. join

The join command joins two files together on the basis of a key field that contains entries common to both of them.

Syntax : $ join filename1 filename2

Example : $ cat country_cap

India              Newdelhi

Pakistan        Islamabad

Australia       Canberra

$ cat players

India           Sachin

Pakistan        Afridi

Australia       Ponting

$ join country_cap players

India            Newdelhi          Sachin

Pakistan        Islamabad          Afridi

Australia       Canberra            Ponting

(III) DIRECTORY RELATED COMMANDS

  1. pwd

The pwd command displays the path of the current working directory

Syntax: $ pwd

Example:

[[email protected] ~]$ pwd

/home/staff/punitha

  1. mkdir

The mkdir command is used to create a new directory in the current working directory.

Syntax: $ mkdir directory_name

Example:

[[email protected] ~]$ mkdir sample

  1. ls

The ls command displays the list of files in the current working directory.

Syntax: $ ls

$ ls [options]

Following are the different options.

a)ls -l  – The files are displayed with their mode, number of links, owner of the file, file

size, modification date & time and filename.

b)ls -t  – The files are displayed in the order of last modification time.

c)ls -a  – Displays all the files including the hidden files.

d)ls -s  – Displays the size of each file.

Example:

[[email protected] ~]$ ls

file1   file2  sample  new

[[email protected] ~]$  ls  -l

-rw-rw-r– 1 punitha punitha    26   2011-02-23 10:42  file1

-rw-rw-r– 1 punitha punitha    38   2011-02-22 10:40  file2

drw-rw-r– 1 punitha punitha    15   2011-02-22 10:41 sample

-rw-rw-r– 1 punitha punitha    20   2011-02-22 10:44  new

  1. cd

a)The cd command is used to change from the current working directory to the specified directory.

Syntax: $ cd directory_name

Example :

[[email protected] ~]$ cd sample

[[email protected] sample] $

b)The cd command when given without any argument takes you to the home directory.

Syntax: cd

Example:

[[email protected] example]$ cd

[[email protected] ~]$

c)The cd command when used with two dots takes you to the parent directory of the current working directory.

Syntax:  cd  ..

  1. rmdir

The rmdir command removes the specified directory. It requires the specified directory to be empty before removing it.

Syntax: $ rmdir directory_name

Example:

[[email protected] ~]$ rmdir sample

A pipe is a mechanism in which the output from one command can be redirected as input to another command.

To send the output of one command as input for another, the two commands must be joined using a pipe ( | ) character.

Example:

1. $ who | wc -l

The output of the command “who” is passed as input to the “wc -l” command.

The above example displays the number of users who have currently logged into the system.

2. $ ls | wc -l

The output of the command “ls” is passed as input to the “wc -l” command.

The above example displays the number of files present in the current working directory.

3. $ ls | grep “^f”

The above example lists all the files beginning with the character ‘f’ on the screen.

4. $ ls | tail -5

The above example displays the list of last 5 files present in the current working directory.

(IV) INPUT/OUTPUT REDIRECTION

              The standard input device is the keyboard and the standard output device is the screen.

Input can be taken from sources other than the standard input and output can be passed to any source other than the standard output. Such a process is called redirection.

INPUT REDIRECTION

         When the input for a command is taken from sources other than the standard input device, then the process is called as input redirection.

Syntax: $ command < filename

Example : $ wc < file1

In the above example, the command “wc” takes its input from the file “file1”.

OUTPUT REDIRECTION

            When the output from a command is sent to sources other than the standard output device, then the process is called as output redirection.

Syntax:  $ command > filename

Example:  who > file2

In the above example, the output of who command is sent to the file “file2” instead of being displayed on the screen.

(V) FILTERS

              A filter is a command which receives data from the standard input, processes it, and sends the results to the standard output.

  1. wc

The wc command counts the number of lines, words and characters in the specified file.

Syntax : $ wc [options] filename

Following are the different options.

a)- l counts the number of lines

b)- w counts the number of words

c)- c counts the number of characters

Example :  $ cat file1

welcome to

unix lab

i)$ wc file1

   2   4  20  file1

ii)$ wc -l file1

   2  file1

iii)$ wc -w file1

   4  file1

iv)$ wc -c file1

   20  file1

  1. sort

The sort command sorts the contents of a file.

Syntax : $ sort [options] filename

Following are the different options.

a)-n Sorts in numeric order

b)-r Sorts in reverse order

c)-u Sorts and displays only the unique output.

Example : $ cat  countries

India

Pakistan

Australia

Australia

i)$ sort countries

Australia

Australia

India

Pakistan

ii)$ sort -u countries

Australia

India

Pakistan

iii)$ sort -r countries

Pakistan

India

Australia

Australia

  1. head

The head command displays the first 10 lines of the specified file by default.

Syntax : $ head [options] filename

Following are the different options.

a)-n  Displays the first n lines of the specified file.

b)-cn  Displays the first n characters of the specified file.

Example :  $ cat countries

India

Pakistan

Australia

Australia

i)$ head -2 countries

India

Pakistan

ii)$ head -c3 countries

Ind

  1. tail

The tail command displays the last 10 lines of the specified file by default.

Syntax : $ tail [options] filename

Following are the different options.

a)-n              Displays the last n lines of the specified file.

b)-cn Displays the last n characters of the specified file.

Example :  $ cat countries

India

Pakistan

Australia

Australia

i)$ tail -2 countries

Australia

Australia

ii)$ tail –c4 countries

lia

  1. uniq

The uniq command removes repeated lines from the specified file.

Syntax : $ uniq [options] filename

Following are the different options.

a)-d Displays only the lines that are duplicated in the input file.

b)-u  Displays only the lines with single occurrences.

c)-c Precedes each line displayed by the number of times it occurs.

Example :  $ cat countries

India

Pakistan

Australia

Australia

i)$ uniq countries

India

Pakistan

Australia

ii)$ uniq –d countries

Australia

iii)$ uniq –u countries

India

Pakistan

iv)$ uniq –c countries

1 India

1 Pakistan

2 Australia

  1. grep

The grep command is used to search for a particular pattern from a file and display those lines on the standard output.

Syntax : $ grep [pattern] filename

Example : $ cat countries

India

Pakistan

Australia

Australia

i) grep “dia” countries

   India

ii) grep “^A” countries (Displays lines that start with A)

    Australia

    Australia

iii) $ grep “n$” countries (Displays lines that end with n)

    Pakistan

  1. nl

The nl command adds line numbers to a file and displays the file.

Syntax :  $ nl filename

Example : $ cat countries

India

Pakistan

Australia

Australia

$ nl countries

1  India

2  Pakistan

3  Australia

4  Australia

  1. cut

The cut command selects particular columns or fields from the specified file and prints them on the standard output.

Syntax :  $ cut  [options] filename

Following are the different options.

a)–c Selects the specified characters from the file and displays them.

b)–f Selects the specified fields from the file and displays them

Example : $ cat  state_cap

Tamilnadu       Newdelhi        Tamil

Andhra            Hyderabad       Telugu

Karnataka       Bangalore        Kannada

[Note:]  Use tab to separate fields.

i) $ cut -f1 state_cap

Tamilnadu

Andhra

Karnataka

ii) $ cut -f1,3  state_cap

Tamilnadu       Tamil

Andhra            Telugu

Karnataka        Kannada

iii) cut -c1 state_cap

T

A

K

  1. colrm

The colrm command removes selected columns from the specified file.

The colrm command,  if called with one parameter the columns of each line will be

removed starting from the specified column. If called with two parameters the columns from the first column to the last column will be removed.

Syntax : $ cut [startcol] [endcol]   <  filename

Example :  $ cat countries

India

Pakistan

Australia

Australia

i) $ colrm 3 <  countries

In

Pa

Au

Au

ii) $ colrm 2 4 < countries

Ia

Pstan

Aralia

Aralia

  1. tr

The tr command translates characters present in the standard input, and writes them to the standard output.

Syntax : $ tr  [input_characters]  [output_characters]   <  filename

Example  :   $ cat countries

India

Pakistan

Australia

Australia

i) $ tr   a   A <  countries

IndiA

PAkistAn

AustrAliA

AustrAliA

ii) $ tr ‘[a-z]’  ‘[A-Z]’ <  countries

INDIA

PAKISTAN

AUSTRALIA

AUSTRALIA

  1. more

The more command displays the contents of a file on the screen page by page. The next

screen can be viewed by pressing the space bar.

Syntax : $ more filename.

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