sed examples

Ref: https://www.geeksforgeeks.org/sed-command-in-linux-unix-with-examples/

sed 's/unix/linux/' test.txt   # Replacing or substituting string (sed command replaces the first occurrence of the pattern in each line and it)

sed 's/unix/linux/2' test.txt  # Replacing the nth occurrence of a pattern in a line

sed 's/unix/linux/g' test.txt  # Replace all occurances in a line as well

sed 's/unix/linux/3g' test.txt # Replace nth till last (3rd, 4th, 5th etc.,)

echo "Welcome To The Geek Stuff" | sed 's/\(\b[A-Z]\)/\(\1\)/g'

sed '3 s/unix/linux/' test.txt # restrict the sed command to replace the string on a specific line number.

sed 's/unix/linux/p' test.txt  # The /p print flag prints the replaced line twice on the terminal. If a line does not have the search pattern and is not replaced, then the /p prints that line only once.

sed -n 's/unix/linux/p' test.txt # print only replaced lines, n option suppresses the duplicate rows generated by the /p flag and prints the replaced lines only one time.

sed '1,3 s/unix/linux/' test.txt # Replace range of lines

sed '5d' test1.txt  # delete 5th line

sed '$d' test1.txt  # delete last line

sed '3,6d' test1.txt # delete from range x to y

sed '12,$d' test1.txt # delete from nth line till last

sed '/abc/d' test1.txt # delete line which matches pattern

# Replace & update same file (-i means --in-place)

sed -i 's/ABC/ABCDEF/g' sed_test.txt

# Replace & update same file (-i means --in-place), -ibak takes original file as backup (sed_test.txtbak)

sed -ibak 's/ABC/ABCDEF/g' sed_test.txt

systemctl chkconfig - Enable/Disable service on boot

chkconfig --list httpd

chkconfig --list varnish

(or)

systemctl list-unit-files | grep httpd

systemctl list-unit-files | grep varnish



systemctl is-active httpd

systemctl is-active varnish


Enable on boot

• chkconfig httpd on

Disable on boot

• chkconfig httpd off

Find Unix Distribution Version

• cat /proc/version
• Linux version 4.14.219-164.354.amzn2.x86_64 (mockbuild@ip-10-0-1-103) (gcc version 7.3.1 20180712 (Red Hat 7.3.1-12) (GCC)) #1 SMP Mon Feb 22 21:18:39 UTC 2021 
• rpm -E %{rhel}
• 7

How to evaluate time taken for urls using curl

• Configure ~/.curlrc
• Add file ~/.curlrc & add the below
• -w "dnslookup: %{time_namelookup} | connect: %{time_connect} | appconnect: %{time_appconnect} | pretransfer: %{time_pretransfer} | starttransfer: %{time_starttransfer} | total: %{time_total} | size: %{size_download}\n"
•  How to call urls using Curl?
• curl -so /dev/null "https://www.site.com/test/video.mp4"
• dnslookup: 0.013 | connect: 0.335 | appconnect: 1.090 | pretransfer: 1.090 | starttransfer: 1.666 | total: 24.770 | size: 128750670
• curl -so /dev/null "https://cdn.site.com/test/video.mp4"
• dnslookup: 0.013 | connect: 0.051 | appconnect: 0.311 | pretransfer: 0.311 | starttransfer: 1.287 | total: 11.556 | size: 128750670

We can observe 2nd url (CDN) takes almost half the time as the first once.

Unix Cut Comamnd

CUT command has lot of advantages in grep/cut the fields/chars from the files easily in no time

We can use CUT command in the following ways:
1) Print Characters by Position (chars)
2) Print Characters by Range (range a-b)
3) Print the fields using the delimiter

Now, we discuss the above mentioned briefly. Let's have fun with some simple examples.
In all the below examples, we use same.txt as input as mentioned below :

sample.txt
Andy,100,Ney york,USA
Arjun,200,New Delhi,India
Venkatesh,300,Chennai,India
Andy,400,Boston,USA
John,500,Chicago,USA


1) Using Cut Print Characters by Position

This command prints the fourth character in each line of the file

]# cut -c4 sample.txt
y
u
k
y
n

This command prints the fourth and sixth character in each line.

]# cut -c4,6 sample.txt
y1
u,
kt
y4
n5

2) Using Cut Print Characters by Range

This command prints the characters from fourth position to the eighth position in each line

]# cut -c4-8 sample.txt
y,100
un,20
kates
y,400
n,500

This command prints the first four characters in a line

]# cut -c-4 sample.txt
Andy
Arju
Venk
Andy
John

This command prints the characters from fourth position to the end

]# cut -c4- sample.txt
y,100,Ney york,USA
un,200,New Delhi,India
katesh,300,Chennai,India
y,400,Boston,USA
n,500,Chicago,USA

This command omits the start and end positions, then the cut command prints the entire line.

]# cut -c- sample.txt
Andy,100,Ney york,USA
Arjun,200,New Delhi,India
Venkatesh,300,Chennai,India
Andy,400,Boston,USA
John,500,Chicago,USA

3) Print the fields using the delimiter
-d  option in cut command can be used to specify the delimiter 
-f  option is used to specify the field position

This command prints the first field of comma separated line

]# cut -d',' -f1 sample.txt
Andy
Arjun
Venkatesh
Andy
John

This command prints the first and second field in each comma separated line

]# cut -d',' -f1,2 sample.txt
Andy,100
Arjun,200
Venkatesh,300
Andy,400
John,500

This command prints the first, second and third field (range 1-3) in each comma separated line

]# cut -d',' -f1-3 sample.txt
Andy,100,Ney york
Arjun,200,New Delhi
Venkatesh,300,Chennai
Andy,400,Boston
John,500,Chicago

This command prints the first two fields in each comma separated line

]# cut -d',' -f-2 sample.txt
Andy,100
Arjun,200
Venkatesh,300
Andy,400
John,500

This command prints from first field to last field in each comma separated line

]# cut -d',' -f1- sample.txt
Andy,100,Ney york,USA
Arjun,200,New Delhi,India
Venkatesh,300,Chennai,India
Andy,400,Boston,USA
John,500,Chicago,USA 

Please refer to other topics on Unix like :
Unix Delete Duplicated Lines in a File
Unix Unique Lines in a File
Unix Grep Examples
Search a Directory in Unix
Unix For Loop
pushd & popd in Unix
Find Size of Directory
Word Count

Please refer to other topics on AWK like :
Awk Examples
Print First Two Columns of File
Print Last Two Columns of File

Please refer to other topics on Dict like :
Dict in Python
Dict keys and values in Python

Please refer to other topics on List like :
List in Python
Append to list in Python
Delete the last name from the list in Python
Remove an element from List in Python
Check an element exists in an list in Python
Python Filter Vs Map Vs List Comprehension

Please refer to other topics on File Concepts like :
Print File Content in Python
Print File in Reverse Order in Python

Please refer to Regular Expressions Concepts :
Brief on Regular Expressions
Greedy Operators in Regular Expressions in Perl
Modifiers in Regular Expressions in Perl
Capturing concept in Regular Expressions in Perl
Capture Pre Match ,Post Match, Exact match in Regular Expressions in Perl
Non Capturing Paranthesis in Regular Expressions in Perl
Substitute nth occurance in Regular Expressions in Perl
All Topics in Regular Expressions in Perl

You might also wish to read other topics like :
Python Class and Object Example
Inheritance in Python
Packages in Python
Exceptions in Python
How to remove duplicate lines from a file in Perl
How to remove duplicate lines from a file in Pyhton

Unix Sort, Uniq, Combine Files

We will discuss about 
1) Combining contents of two files in Unix 
2) Sort & Get the Unique Lines (delete duplicate lines)
3) How to get only the duplicate lines
4) How to get only the unique lines

Suppose we have two files a.txt and b.txt as mentioned below :

a.txt

10
20
30
40
50

b.txt

10
20
30
40
50
60
70
80

1) Combining contents of two files in Unix 
Combining contents of both a.txt & b.txt into c.txt
]# cat a.txt b.txt > c.txt 

10
20
30
40
50
10
20
30
40
50
60
70
80

2) Sort and Get the Unique Lines (delete duplicate lines)
]# cat c.txt | sort | uniq

10
20
30
40
50
60
70
80

3) How to get only the duplicate lines
]# cat c.txt | sort | uniq -u

60
70
80

4) How to get only the unique lines

10
20
30
40
50

5) How to get sort by ignore case
]# cat requirements.txt | sort --ignore-case > requirements_bak.txt 

Please refer to other topics on Unix like :
Unix Grep Examples
Search a Directory in Unix
Unix For Loop
pushd & popd in Unix
Find Size of Directory
Word Count

Please refer to other topics on AWK like :
Awk Examples
Print First Two Columns of File
Print Last Two Columns of File

Please refer to other topics on Dict like :
Dict in Python
Dict keys and values in Python

Please refer to other topics on List like :
List in Python
Append to list in Python
Delete the last name from the list in Python
Remove an element from List in Python
Check an element exists in an list in Python
Python Filter Vs Map Vs List Comprehension

Please refer to other topics on File Concepts like :
Print File Content in Python
Print File in Reverse Order in Python

Please refer to Regular Expressions Concepts :
Brief on Regular Expressions
Greedy Operators in Regular Expressions in Perl
Modifiers in Regular Expressions in Perl
Capturing concept in Regular Expressions in Perl
Capture Pre Match ,Post Match, Exact match in Regular Expressions in Perl
Non Capturing Paranthesis in Regular Expressions in Perl
Substitute nth occurance in Regular Expressions in Perl
All Topics in Regular Expressions in Perl

You might also wish to read other topics like :
Python Class and Object Example
Inheritance in Python
Packages in Python
Exceptions in Python
How to remove duplicate lines from a file in Perl
How to remove duplicate lines from a file in Pyhton

Unix Shortcuts 1

a) !!    #to run the previous command 

e.g.,
>>pwd
>>!!  #executes "pwd" command

b) Control+P #move up through history list, one command at a time. (Up arrow key) 

c) Control+N #move down (or Down arrow key). 

d) !n #run nth command in history list. where n is a number from your history list. 

e.g.,
>>history

1 ls
2 pwd
3 vim test.txt
4 vim ~/aliases
5 vim ~/.vimrc
6 history

>>!3 #runs 3rd command in the history i.e., vim test.txt
>>!-2 #runs 2nd command from the end of history i.e., vim ~/.vimrc

e) !n:p   #only preview command number n (will not execute the command). 

f) !string   #Run most recent command starting with characters in string.

e.g.,

>>vim text.txt
>>pwd
>>ls -lrt
>>mkdir test
>>!vim     press<Enter> #Runs most recent command starting with "vim"
>>!ls press<Enter> #Runs most recent command starting with "ls"

g) Move the cursor to beginning of line in Unix Terminal
Beginning of line     Ctrl+a

h) Move the cursor to end of line in Unix Terminal
End of line           Ctrl+e

Find Files Using a Wildcard in UNIX

- Find command checks recursively in all the folders present with in that path

find files ending with "py" in current directory recursively
find . -iname \*.py

find files starting with prel_log in "/" directory recursively
find / -name perl_log\* -print

- The backslash \ character is important
- It tells the shell not to treat the wildcard character as a wildcard.

Unix How to Find a Particular Directory

We know how to find a file in Unix directories using

This will search sample.txt in current directory

#]find . -iname sampe.txt


But if we want to find out a particular directory in the unix, type -d denotes search for directory

#] find / -name mysql -type d
/var/log/mysql
/var/lib/mysql
/var/lib/mysql/mysql
/etc/mysql
/usr/lib/perl5/DBD/mysql
/usr/lib/perl5/auto/DBD/mysql
/usr/share/mysql


In order to narrow down the search, you could mention exact path (/etc) where you want to search

#] find /etc -name mysql -type d
/etc/mysql

Unix For Loop

#]mkdir for_test_dir1

#]mkdir for_test_dir2

#]mkdir for_test_dir3

#]cat for_test_dir1/for_test.txt
content 1
content 1
content 1

#]cat for_test_dir2/for_test.txt
content 2
content 2
content 2

#]cat for_test_dir3/for_test.txt
content 3
content 3
content 3
...
...

#] ls
for_test_dir1 for_test_dir2 for_test_dir3 for_test_dir4 for_test_dir5
......
......


#]foreach var (`ls`)
foreach? ls -ltr $var/for_test*
foreach? end

O/P:
It will list all the for_test files present in for_test_dir's

pushd popd example

When you have  to work with navigate different directories quickly, its difficult to remember the whole path or type the whole thing again and again.

There is concept in Linux/Unix to manipulate directory stack, you can use directory stack to push directories into it and later pop directory from the stack.

1) dirs : Display the current directory stack without pushing or popping a new directory

2) pushd : Push directory into the Stack

3) popd : Pop directory from the Stack

Using pushd and popd effectively can help you get around your command-line environment quickly


E.g.,

]# mkdir /usr/local/dir1

]# mkdir /usr/local/dir2

]# mkdir /usr/local/dir3

]# dir
~

]# pushd /usr/local/dir1

]# dir
/usr/local/dir1   ~


]# pushd /usr/local/dir2


]# dir
/usr/local/dir2   /usr/local/dir1   ~

]# pushd /usr/local/dir3

]# dir
/usr/local/dir3   /usr/local/dir2   /usr/local/dir1   ~


]# popd

]# pwd
/usr/local/dir3

]# dir
/usr/local/dir2   /usr/local/dir1   ~


]# popd

]# pwd
/usr/local/dir2

 ]# dir
/usr/local/dir1   ~


]# popd


]# pwd
/usr/local/dir1

 ]# dir
~

How to find the size of a directory in linux

We all know "du" command gives the size of the files, but it not convenient to read or understand the size as "du" command gives the size in KB's

In order to  make is human readable format, please follow as mentioned below


du -lsh <directory_name>

du -lsh <file_name>

-h => display the size in human readable format

e.g.,
>> du  -lsh  prabhath_movies
5GB  prabhath_movies

>> du  -lsh  hero.avi
1GB   hero.avi


Thanks for going through this article, Have a good day :-)

Cron Job Basics - Crontab

crontab -e      Edit your crontab file, or create one if it doesn’t already exist.
crontab -l      Display your crontab file.
crontab -r      Remove your crontab file.
crontab -v      Display the last time you edited your crontab file. (This option is only available on a few systems.)


min    0-59
hour   0-23
day    1-31
mon    1-12
dow    0-6 (Sunday = 0, Saturday = 6) DOW => Day of Week


min hr day month Week
30 00 01 01,06,12 * –> 00:30 Hrs on 1st of Jan, June & Dec.
00 20 * 10 01-05 –> 8.00 PM every weekday (Mon-Fri) only in Oct
00 00 01,10,15 * * –> midnight on 1st ,10th & 15th of month
05,10 00 10 * 01 –> At 12.05,12.10 every Monday & on 10th of every month
05 00 01 01 * -> 00:05 Hrs on 1st of Januray of each year

The asterisk in the field indicates to cron that any day of the week is acceptable.
However, since an explicit month and day have been specified, the day of the week is effectively ignored.


How to create a cron job that will run on the last day of each month, considering the fact that a month could have 28, 29, 30 or 31 days ?

Ans:
Your script, however, can test for that and exit if it is not the last day.
So - you'd set it in cron to run on the 28, 29, 30 and 31. Your script decides if it really is the last day and exits if it is not.
Or you can put each month into crontab separately and just deal with February in your script.


min hr day month Week
30 20 28,29 02 * /usr/prabhath/run.pl -> 8.30 PM every 28th of Feb
30 20 30 04,06,09,11 * /usr/prabhath/run.pl -> 8.30 PM every 30th of Months having 30 days
30 20 31 01,03,05,07,08,10,12 * /usr/prabhath/run.pl -> 8.30 PM every 31th of Months having 31 days

More Examples:
################
min hr day month Week User Command
01 * * * * root echo "This command is run at one min past every hour"
17 08 * * * root echo "This command is run daily at 8:17 am"
17 20 * * * root echo "This command is run daily at 8:17 pm"
00 04 * * 0 root echo "This command is run at 4 am every Sunday"
42 04 01 * * root echo "This command is run 4:42 am every 1st of the month"
01 * 19 07 * root echo "This command is run hourly on the 19th of July"


Example:
############
min hr day month Week User Command
* 12 16 * Mon root cmd

Will run cmd at midday every Monday and every 16th, and will produce the
same result as both of these entries put together would:
* 12 16 * * root cmd
* 12 * * Mon root cmd

Example:
############

min hr day month Week User Command
59 11 * * 1,2,3,4,5 root backup.sh
equals to
59 11 * * 1-5 root backup.sh


Step Values:
#################
Cron also supports 'step' values.
*/2 in the dom field would mean the command runs every two days and likewise,
*/5 in the hours field would mean the command runs every 5 hours.

Example:
############

min hr day month Week User Command
* 12 10-16/2 * * root backup.sh
is the same as:
* 12 10,12,14,16 * * root backup.sh

E.g.,

min hr day month Week User Command
*/15 9-17 * * * root connection.test
Will run connection.test every 15 mins between the hours or 9am and 5pm


min hr day month Week User Command
* 12 1-15,17,20-25 * * root cmd
Will run cmd every midday between the 1st and the 15th as well as the 20th and 25th (inclusive) and also on the 17th of every month.


O/P from Cron:
###################

min hr day month Week User Command
*/15 9-17 * * * root connection.test | mail -s "Subject" prabhathkota@gmail.com

*/15 9-17 * * * root connection.test >/dev/null 2>&1 #It won't send mail to anyone

*/15 9-17 * * * root connection.test > log.file

*/15 9-17 * * * root connection.test > log.file 2>&1

*/15 9-17 * * * root connection.test > mail -s "logfile for cmd" <log.file

*/15 9-17 * * * root connection.test >


Disable Email in Cronjob
#########################
By default cron jobs sends a email to the user account executing the cronjob. If this is not needed put the following command At the end of the cron job line .
>/dev/null 2>&1

Word Count - Unix

>> wc test.txt

15  43 282 test.txt

ie.,

15 lines
43 words
282 chars


>>wc -l test.txt    #Lines
15 test.txt


>> wc -c test.txt    #Words
282 test.txt


>> wc -w test.txt    #Characters
43 test.txt

How to print first two columns of a file - AWK

1) It will print first line alone

>>awk 'NR==1' test.txt #1st line from the top
>>awk 'NR==7' test.txt #7th line from the top

2) How to print first line/lines of the file

>>head -8 test.txt

How to print last two columns of a file - AWK

1) How to print last two columns of a file?

NF => prints the last line

>>cat test.txt
prabhath   kota   Jan
lakshmi     muvvala   Feb
PRABHATH    KOTA   Mar
LAKSHMI       MUVVALA   Apr

>>awk '{print $(NF-1),"\t",$NF}' test.txt #RIGHT

output:
kota              Jan
muvvala         Feb
KOTA           Mar
MUVVALA  Apr

>>awk '{print $NF-1,"\t",$NF}' test.txt #WRONG


2) How to print last two columns of a command?

>> ls
-rw-r----- 1 kotaprax users 203 Nov 22 12:51 a.txt
-rw-r----- 1 kotaprax users 282 Nov 23 10:18 b.txt
-rw-r----- 1 kotaprax users  17 Nov 16 15:25 c.txt

>>ls -l | awk '{print $(NF-1),"\t",$NF}'

output:
12:51 a.txt
10:18 b.txt
15:25 c.txt


3) How to print the last line/lines of the file

>>tail -f test.txt
>>tail -4 test.txt #Prints Last 4 lines
>>tail -1 test.txt #Prints Last line of the file

Awk Examples

1) To fetch selected columns from a command using AWK

e.g.,

>> ls -l

-rw-r----- 1 kotaprax users 203 Nov 22 12:51 new.txt
-rw-r----- 1 kotaprax users 100 Nov 22 12:51 new1.txt
-rw-r----- 1 kotaprax users 126 Nov 23 12:57 output.txt
-rw-r----- 1 kotaprax users 282 Nov 23 10:18 test.txt
-rw-r----- 1 kotaprax users  17 Nov 16 15:25 test1.txt

From the abvoe command, we are deriving some columns

>> ls -l | awk '{print $3 "\t" $8 "\t" $9}'
             
kotaprax        12:51   new.txt
kotaprax        12:51   new1.txt
kotaprax        12:57   output.txt
kotaprax        10:18   test.txt
kotaprax        15:25   test1.txt



2) How to print first column from the file using AWK

e.g.,

>> cat test.txt
prabhath kota
lakshmi muvvala
PRABHATH KOTA
LAKSHMI MUVVALA


>>awk '{print $1}' test.txt
(or)
>>awk < test.txt '{ print $1 }'

o/p:
>>cat test.txt
prabhath
lakshmi
PRABHATH
LAKSHMI


3) How to copy the files using AWK

>> ls
a.txt
b.txt
c.txt

It will copy file.txt to file.txt.new for all the txt files

>>ls *.txt | awk '{print "cp "$1" "$1".new"}' | sh

o/p:

>> ls
a.txt
b.txt
c.txt
a.txt.new
b.txt.new
c.txt.new


4) How to list only directories using awk

>>ls
a.txt
b.txt
c.txt
prabhath_test

o/p:

>> ls -l | grep '^d'
#Lists only directories, since directories start with
drwxr-x--- 2 kotaprax users 1024 Nov 23 13:57 prabhath_test


>>ls -l | grep -v '^d' #Lists only files but not directories
-rw-r----- 1 kotaprax users 203 Nov 22 12:51 a.txt
-rw-r----- 1 kotaprax users 282 Nov 23 10:18 b.txt
-rw-r----- 1 kotaprax users  17 Nov 16 15:25 c.txt


5) Remove files using AWK

>>ls
a.txt
b.txt
c.txt
prabhath_test
a.tt
b.tt

>> ls -l *.tt | awk '{print "rm -r "$9}' | sh
#"rm" is a command, in order to execute, "sh" is used

o/p:

>>ls
a.txt
b.txt
c.txt
prabhath_test



6) AWK - Difference between $0 and $1

>> echo "hello1 hello2 hello3" | awk ' {print $0} ' #$0 prints the whole
hello1 hello2 hello3

>> echo "hello1 hello2 hello3" | awk ' {print $3} ' #$1 prints 1st column
hello3



7) How to print 1st column of a file into another file ?

>>cat test.txt
prabhath kota
lakshmi muvvala
PRABHATH KOTA
LAKSHMI MUVVALA

>> awk '{print $1}' test.txt > output.txt

o/p:

>>cat test.txt
prabhath
lakshmi
PRABHATH
LAKSHMI

Unix Grep Examples

Grep
######

1) How to exclude lines in a grep

syntax: grep -v <pattern> <filename>

e.g.,
>> cat test.txt
prabhath
ramesh
vamsi
lakshmi muvvala
PRABHATH
LAKSHMI MUVVALA

>> grep -v "prabhath" test.txt

It will exclude the lines which contain "prabhath"

o/p:
ramesh
vamsi
lakshmi muvvala
PRABHATH
LAKSHMI MUVVALA


2) How to exclude lines in a grep with ignore case

syntax: grep -iv <pattern> <filename>

e.g.,
>> cat test.txt
prabhath
ramesh
vamsi
lakshmi muvvala
PRABHATH
LAKSHMI MUVVALA

>> grep -iv "prabhath" test.txt

It will exclude the lines which contain "prabhath", "Prabhath", "PRABAHTAH" etc.,

o/p:
ramesh
vamsi
lakshmi muvvala
LAKSHMI MUVVALA

3) How to exclude lines which contain multiple patterns at one shot

Syntax: grep -v -e <pattern> -e <pattern> <filename>

e.g.,
>> cat test.txt
prabhath
ramesh
vamsi
lakshmi muvvala
PRABHATH
LAKSHMI MUVVALA


>>grep -v -e "prabhath" -e "lakshmi" test.txt

It will exclude the lines which contains the pattern "prabhath" & pattern "lakshmi"

o/p:
ramesh
vamsi
PRABHATH
LAKSHMI MUVVALA


>>grep -iv -e "prabhath" -e "lakshmi" test.txt

Please note "i" - ignore case
It will exclude the lines which contains the pattern "prabhath", "PRABHATH" & pattern "lakshmi", "LAKSHMI"

o/p:
ramesh
vamsi


4) Counting the number of matches using grep -c

Syntax: grep -c "pattern" filename

e.g.,
>> cat test.txt
prabhath
ramesh
vamsi
lakshmi muvvala
PRABHATH
LAKSHMI MUVVALA

>>grep -c "prabhath" test.txt
1

>>grep -ic "prabhath" test.txt
2


5) Counting the number of lines that does not match the pattern

e.g.,
>> cat test.txt
prabhath
ramesh
vamsi
lakshmi muvvala
PRABHATH
LAKSHMI MUVVALA

>>grep -vc prabhath test.txt
5

(or)

>>grep -v -c prabhath test.txt
5


6) Display N lines around match (Before & After)

Syntax: > grep -C 2 "Pattern" File

e.g.,
>> cat test.txt
prabhath
ramesh
vamsi
lakshmi muvvala
PRABHATH
LAKSHMI MUVVALA


>> grep -C 2 "lakshmi" test.txt

o/p:
ramesh
vamsi
lakshmi muvvala //Actual Match
PRABHATH
LAKSHMI MUVVALA


7) Display N lines Before Match

Syntax: > grep -B 2 "Pattern" File

e.g.,
>> cat test.txt
prabhath
ramesh
vamsi
lakshmi muvvala
PRABHATH
LAKSHMI MUVVALA

>> grep -B 2 "lakshmi" test.txt

o/p:
ramesh
vamsi
lakshmi muvvala //Actual Match


8) Display N lines After Match

Syntax: >> grep -A 2 "Pattern" File

e.g.,
>> cat test.txt
prabhath
ramesh
vamsi
lakshmi muvvala
PRABHATH
LAKSHMI MUVVALA

>> grep -A 2 "lakshmi" test.txt

o/p:
lakshmi muvvala //Actaul Match
PRABHATH
LAKSHMI MUVVALA


9)  Checking for full words, not for sub-strings using grep -w

e.g.,
>> cat test.txt
prabhath
prabhathkota
prabhath kota
ramesh
vamsi
lakshmi muvvala
PRABHATH
PRABHATHKOTA
PRABHATH KOTA
LAKSHMI MUVVALA

Syntax: >> grep -w "Pattern" File

>>grep -iw "kota" test.txt

o/p:
prabhath kota
PRABHATH KOTA


>>grep -i "kota" test.txt

o/p:
prabhathkota
prabhath kota
PRABHATHKOTA
PRABHATH KOTA


10) How to get line numbers in grep

>> cat test.txt
prabhath
prabhathkota
prabhath kota
ramesh
vamsi
lakshmi muvvala
PRABHATH
PRABHATHKOTA
PRABHATH KOTA
LAKSHMI MUVVALA


>> grep -n 'PRABHATH' test.txt

o/p:
7 PRABHATH
8 PRABHATHKOTA
9 PRABHATH KOTA

>> grep -in 'PRABHATH' test.txt

o/p:
1 prabhath
2 prabhathkota
3 prabhath kota
7 PRABHATH
8 PRABHATHKOTA
9 PRABHATH KOTA


11) Grep Pipe Examples

1) Display cpu model name

#With Pipe
]# cat /proc/cpuinfo | grep -i 'Model'

#Without Pipe
]# grep -i 'Model' /proc/cpuinfo    

2) grep dbname *.dbl | grep mysql


12) Some complex examples using Grep...

>> cat test.txt
prabhath
prabhathkota
prabhath kota
ramesh
vamsi
lakshmi muvvala
PRABHATH
PRABHATHKOTA
PRABHATH KOTA
LAKSHMI MUVVALA


>> grep -nC 2 'lakshmi' test.txt

Note: "-C 2" will grep for 2 lines above and 2 lines below
          "-n" will give the line numbers

o/p:
4 ramesh
5 vamsi
6 lakshmi muvvala
7 PRABHATH
8 PRABHATHKOTA


13) Grep OR

1) grep 'pattern1\|pattern2' filename

$ cat employee.txt
100  Thomas  Manager    Sales       $5,000
200  Jason   Developer  Technology  $5,500
300  Raj     Sysadmin   Technology  $7,000
400  Nisha   Manager    Marketing   $9,500
500  Randy   Manager    Sales       $6,000


$ grep 'Tech\|Sales' employee.txt
100  Thomas  Manager    Sales       $5,000
200  Jason   Developer  Technology  $5,500
300  Raj     Sysadmin   Technology  $7,000
500  Randy   Manager    Sales       $6,000

2) grep -E 'pattern1|pattern2' filename

$ grep -E 'Tech|Sales' employee.txt
100  Thomas  Manager    Sales       $5,000
200  Jason   Developer  Technology  $5,500
300  Raj     Sysadmin   Technology  $7,000
500  Randy   Manager    Sales       $6,000


3) egrep 'pattern1|pattern2' filename

$ egrep 'Tech|Sales' employee.txt
100  Thomas  Manager    Sales       $5,000
200  Jason   Developer  Technology  $5,500
300  Raj     Sysadmin   Technology  $7,000
500  Randy   Manager    Sales       $6,000


14) Grep AND

grep -E 'pattern1.*pattern2' filename
grep -E 'pattern1.*pattern2|pattern2.*pattern1' filename

$ grep -E 'Dev.*Tech' employee.txt
200  Jason   Developer  Technology  $5,500

The following example will grep all the lines that contain both “Manager” and “Sales” in it (in any order).
$ grep -E 'Manager.*Sales|Sales.*Manager' employee.txt


15) Grep NOT

grep -v 'pattern1' filename

$ grep -v Sales employee.txt
200  Jason   Developer  Technology  $5,500
300  Raj     Sysadmin   Technology  $7,000
400  Nisha   Manager    Marketing   $9,500

$ egrep 'Manager|Developer' employee.txt | grep -v Sales
200  Jason   Developer  Technology  $5,500
400  Nisha   Manager    Marketing   $9,500


16) Highlighting the search using GREP_OPTIONS

$ export GREP_OPTIONS='--color=auto' GREP_COLOR='100;8'

$ grep this demo_file
this line is the 1st lower case line in this file.
Two lines above this line is empty.
And this is the last line.



17) Show only the matched string

#] grep -o  

$ grep -o "is.*line" demo_file

is line is the 1st lower case line
is line
is is the last line

Another way to delete old files in perl

Note: 

1) Please remove comment (#)

2) 'unlink' is the command used to remove file in Unix

#!perl
foreach my $file (</path/to/logs/*.log>) {
  next unless -M $file > 7;
  print "Deleting the File $file...\n";
  # unlink $file or die "Failed to remove file $file: $!";
}

-->

Delete files older than X days on Linux

find /path/to/files* -mtime +5 -exec rm {} \;

This is an example, which deletes files older than 5 days from unix command line itself

Note:
1)  Apply this from unix command line itself