Bsic Unix commands

Cat: - it is used to create new files (or) to Open existing files (Or) Append data to the existing files

Syntax: - Cat > File Name

                Ctrld [save & close]

How to open a file

Cat < filename (or) cat filename

Appending data to the file

Cat>> filename

          Ctrl D

It append data at the end of the file

How to open multiple files

Cat file1 file2------file N

Ex: - cat emp1 emp2 emp3

Touch: - it is used to create empty file [0 byte file]

Syntax: - Touch filename

Creating multiple files

Syntax: - Touch file1 file2 file3

By using cat>> we can enter data into the files which were created by touch

How to delete files

Syntax: - rm filename

Rm –I file name [it deletes files with conformation message] delete file Y/N

Rm –f filename [it delete file F-forcibly]

Deleting multiple files

Syntax: rm file1 file2 file3 ----- file N

Working with directories

Syntax:- Mkdir dirname    [it is used to create a new directory

PWD [present working directories]

CD: - to change the directory

Syntax:- cd dirname

Cd abc

    Pwd

Cd..

To come out from current directory

Cut: - it is used to retrieve specific fields and specific characters in a given file

Cut –f 2, 4 filename [it displays 2^nd field to 5^th field file details

Cut –d “,” –f 2, 4 filename [here ‘,’ is the delimiter, it display 2 and 4 fields from file]

Cut –c 1-5 filename [c means character to character, it displays every line first character to fifth character]

Paste:-It is used to join two (or) more files horizontally by using delimiter

Syntax: - Paste filename1 filename2

Grep :- it is used to search a string (or) regular expression in a file

Syntax: - Grep techno file    [ grep pattern filename(s)]

Grep sachin file1 file2 file3

Grep sachin* [it searches in current directory all files]

Note: - if string contains more than one word it must enclosed with in double quotes, otherwise second word becomes file name

Ex: - “sachin sehwag” filename

Grep command options:-

1) Grep –i Sachin filename [to ignore case sensitive]

2) Grep –c Filename

3) Grep –n Sachin filename [it prints lines with line numbers containing the given pattern]

4) Grep-l Sachin* [it gives only filename containing given pattern

5) Grep –V “Sachin Sehwag” filename [it prints the line do not containing the given pattern

6) Grep –O Sachin filename [print only the pattern]

Any String contains wildcard character known as regular expression (or) pattern

The Patterns are classified into 3 types

1. Character pattern

The default pattern is character pattern

1)       Grep “Sachin*” filename

2)      Grep “b[aeiou]ll” sample

Output: - Ball, bell, bill, boll, bull,[this word are matched]  bfll [it is wrong]

3)      Grep “b..d” filename

Output: - band, bold, b$#d, bad

Note: - “.” Is a wild card character

2. Word Pattern

4)      Grep “\<Samsung\> filename [starting of the word]

(or)

            Grep-w “samsung” filename

5)      Grep “Samsung\> filename [ending of the word]

3. Line Pattern

^ => Start of the line

$ => end of the line

1). Grep “^d” filename                                 3). Grep “[bkt]” filename

Output: - do, dog, doing                               Output: - b - -, k- -, t- -

2). Grep “^the” filename             4). Grep “^ [^bkt]” filename [if ^ is inside then it means as not]

Output: - the, then, there            Output: - a--, c--, u--

5). Grep “t$” filename [it shows lines ending with ‘T’]

6). Grep “[0-9] $” filename [it shows lines ending with “digit”]

7). Grep “^…$” filename [line having 3 characters]

8) Grep “\$$” filename [displays line ending with $]

9) Grep “^$” filename [it prints no of empty lines

How to delete empty lines from file

10) Grep –v “^$” filename >temp

                Mv temp filename

F Grep [faster Grep]:-

*It is used to search multiple strings but it doesn’t used to search regular expression

*it searches the strings faster than the grep command.

11) Fgrep “unix

                     Perl

                   Oracle Filename

*Every string must separated by enter key

E Grep [extended Grep]:-

It is a combination of grep and f grep plus additional some regular expressions.

Additional Regular Expressions:-

*[;] :- it matches any one string in the given list

E Grep “(unix:oracle:perl)” filename

*{M} :- it matches exact occurrence of it’s proceeding character

Ex: - ab{3}c

Output: - abbbc

Sed [Stream editor]

It is used to replace a string and it is used for multipurpose filter command

1)      Sed “s/oldstring/newstring/g” filename

2)      Sed “s|^$|I like unix|” filename [it will replace all empty lines with “I like unix”

3)      Sed “s|unix||gi” filename [ it delete “unix” word from file]

4)      Sed –n ‘3p’ filename [How to print 3^rd row/record/line from file]

5)      Sed –n ‘2,5p’ filename [it prints 2^nd record to 5^th records from file]

6)      Sed –n ‘$p’ filename [it prints last record from file]

7)      Sed –n ‘1p

$p’ filename [it prints first and last record from file]

8)      Sed ‘3d’ filename [it deletes 3^rd record from file]

9)      Sed ‘2,5w file1’ file2 [ it copies 2-5 records from file2 to file1

How to add a header line say “Employee, EmpId” to this file using sed?

Sed -i ‘1a or (1i) Employee, EmpId’ empFile {‘1a’ means after it’ll insert ‘1i’ it’ll insert 1st record, like we can add any record any were}

Print lines which contain the character 'u' or 'x' 

sed -n '/[ux]/p' file

Print every alternate line:

Sed ‘n;d' file  N command prints the current line, and immediately reads the next line into pattern space. D command deletes the line present in pattern space. In this way, alternate lines get printed

To add something to the beginning of a every line in a file, say to add a word Fruit:
sed 's/^/Fruit:/’filename

Similarly, to add something to the end of the file

sed 's/$/Fruit:/’filename

To replace or substitute a particular character, say to replace 'a' with 'A'.

sed 's/a/A/' FileName

To replace only the 2nd occurrence of a character

sed 's/a/A/2g’filename

To replace 'a' only in a specific line say 3rd line, not in the entire file:

sed '3s/a/A/g’filename

To replace or substitute 'a' on a range of lines, say from 1st to 3rd line:

sed '1,3s/a/A/g’filename

Using sed, we can also do multiple substitutions. For example, say to replace all 'a' to 'A', and 'p' to 'P':

sed 's/a/A/g; s/p/P/g’ filename  (or) sed 's/a/A/g’ -e ‘s/p/P/g’ filename

Find sum of all columns / numbers in a line

1, Sed ‘s/ /+/g’ FileName | bc example:- 10 20 30 OutPut:- 60

2, Sed ‘s/,/+/g’ FileName | bc  example:- 10,20,30 OutPut:- 60

Sort:-

*It is used to sort the file contents

*By default it sorts the file contents based on ASCII values

*The default order is ascending order

1) Sort filename

2) sort –r filename (reverse ex:- descending)

3) sort –u filename [it displays unique lines in the file

Unique:-

It displays unique lines in the file but the file contents must be in sorted order

1)       Uniq filename

2)       Uniq –u filename [ it displays non duplicated lines

3)       Uniq –d filename [it displays only duplicated lines

4)       Uniq –c filename [it counts how many times each line repeated in the file]

5)       Uniq –u filename>temp

Mv temp >filename [how to delete duplicated rows fromfile]

Tee:-

It is used to write data to the file as well as to the screen

1)      Cat emp !tee file