Grep command with Examples

Grep :

grep command is one of the most frequently used UNIX command stands for "Global Regular Expression Print"  like  find, chmod or tar command in Unix. grep command in Unix operating system e.g. Linux, Solaris, BSD, Ubuntu or IBM AIX is used to search files with matching patterns, by using grep command in Unix you can search a file which contains a particular word or particular pattern.

grep -v you can list down all files which doesn't contains a word i.e. excluding files which matches a pattern

grep -c will print count of matching pattern in a file etc. One of the popular example of  grep command is to find empty files and directories in Unix.

grep command in Unix Example 1: 
Finding relevant word and exclusion of  irrelevant word. Most of the time I look for Exception and Errors in log files and some time I know certain Exception I can ignore so I use grep -v option to exclude those Exceptions

grep Exception logfile.txt | grep -v ERROR

This grep command example will search for word "Exception" in logfile.txt and print them but since we have piped out of first grep command to second grep command which will exclude all lines which match world "ERROR".  To make this grep example more concrete let's see another example, here we have a file which contains three lines  as shown below :

$ cat example.txt
UNIX operating system
UNIX and Linux operating system
Linux operation system

Now we want to search all lines in file example.txt which contains word UNIX but same time doesn't contain world Linux.
 

$ grep UNIX example.txt
UNIX operating system
UNIX and Linux operating system

Now to exclude all lines which contains Linux we will apply another grep command in this output with option -v to exclude matching word as shown in below grep command :

$ grep UNIX example.txt  | grep -v Linux
UNIX operating system

Grep command Example 2: 
If you want to count of a particular word in log file you can use grep -c option to count the word. Below example of command will print how many times word "Error" has appeared in logfile.txt.

grep -c "Error" logfile.txt

If we apply this grep command on our example file to find how many lines contains  word e.g. UNIX has occurred in the file :

$ grep -c UNIX example.txt

2

Difference b/w find and grep commands:

Find command is used to search for a file with a specific file name in a set of files.

Syntax: find .-name "fileE" -print

Ex:

find command is to used find files from the directory

ex :find . -name raju            (Here raju is the file name)

      find . -type f                    (it will list all the files in curent directory)

      find .-perm 777              (it wil list all the files whose having permissions with 777)

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grep command is used to search pattren within a file.

Syntax: grep "pattren" filename

Ex: it used to search the contents inside the file

for suppose take a file by name raju

it contains

hat

bat

soap

SOAP

cat raju

hat

bat

soap

SOAP

now if u want see the word hat where it is is located

grep -i hat *

grep -i hat raju

grep -a hat raju

$ find . -type grep "unix"

$ find . -type grep  -i "unix"

...this command will search all file (from all directories not only from current directory) having word unix. While if use only command grep "unix", it will search only in current directory.

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To find the string in all the files

grep <string> *

Search for a given string in all files recursively

$ grep -r "raju" *

To find the string in the files in all the sub directories

find . -type f -print | grep <string>

To know our AIX Version is http or openssl

root@nabdcweb2:/#lslpp -l | grep http

root@nabdcweb2:/#lslpp -l | grep openssl

  openssl.base            0.9.8.1800  COMMITTED  Open Secure Socket Layer

  openssl.license         0.9.8.1800  COMMITTED  Open Secure Socket License

  openssl.man.en_US       0.9.8.1800  COMMITTED  Open Secure Socket Layer

  openssl.base            0.9.8.1800  COMMITTED  Open Secure Socket Layer

To find which java files was stuck

bash-3.2$ps -ef | grep java

bash-3.2$ps -ef | grep TEST  (TEST is an Appserver domain name)

bash-3.2$ps -ef | grep ora_

To kill the process use below command

bash-3.2$kill -9 processid

Examples of grep commands

1)grep - globally search for a regular expression and print all lines containing it.

tsd1 $ ls -ltr | grep "Aug"  (This command will show the details of folder which was in august month)

o/p:

-rwxrwxrwx 1 tsd1 psoft 351 Aug 8 2011 peopletools.properties

drwxrwxrwx 4 tsd1 psoft 96 Aug 8 2011 appserv

-rwxrwxrwx 1 tsd1 psoft 17 Aug 23 2011 obfuscate.txt

drwxrwxrwx 3 tsd1 psoft 96 Aug 26 2011 oradiag_tsd1

2)if you want both upper and lower case -- use option -i

tsd1 $ ls -ltr | grep -i "People"    (This command will search for the particular folder like People)

O/P:

-rwxrwxrwx 1 tsd1 psoft 351 Aug 8 2011 peopletools.properties

3) if you want zero or more of seaching .*

tsd1 $ ls -ltr | grep -i ".*java"  (This command will search for java files or folders that started with name of java)

O/P:

-rwxrwxrwx 1 tsd1 psoft 9750 Jan 4 01:00 java3.log

-rw-rw-r-- 1 tsd1 psoft 0 Jan 15 01:01 java2.log.lck

-rwxrwxrwx 1 tsd1 psoft 0 Jan 15 01:01 java2.log

-rw-rw-r-- 1 tsd1 psoft 0 Jan 15 01:01 java1.log.lck

4) The sort option +4n skips four fields (fields are separated by blanks) then sorts the lines in numeric order.

ls -l | grep "Aug" | sort +4n

O/P:

-rwxrwxrwx 1 tsd1 psoft 17 Aug 23 2011 obfuscate.txt

drwxrwxrwx 3 tsd1 psoft 96 Aug 26 2011 oradiag_tsd1

drwxrwxrwx 4 tsd1 psoft 96 Aug 8 2011 appserv

-rwxrwxrwx 1 tsd1 psoft 351 Aug 8 2011 peopletools.properties

5) pg command - to see page by page

$ pg filename   (If any page is having more pages then this is used to view that page by page by pressing enter key)

$To search the word in multiple files

# cat file1 file2 file3 | grep /word search

How to know RAM Size in AIX or LINUX

# lsconf | grep Memory

bash-3.2$ lparstat -i | grep Memory

O/P:

            Online Memory                              : 23296 MB( In the entire server this 22.75 GB Ram we are utilizing)

            Maximum Memory                             : 30720 MB

            Minimum Memory                             : 18432 MB

            Memory Mode                                : Dedicated

            Total I/O Memory Entitlement               : -

            Variable Memory Capacity Weight            : -

            Memory Pool ID                             : -

            Physical Memory in the Pool                : -

            Unallocated Variable Memory Capacity Weight: -

            Unallocated I/O Memory entitlement         : -

            Memory Group ID of LPAR                    : -

            Desired Memory                             : 23296 MB( This is allocate RAM Size of the entire server)

            Target Memory Expansion Factor             : -

            Target Memory Expansion Size               : -

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To search the word in the text file

bash-3.2# grep -r "column" /home/script.sh    (It will search the "column" word in "script.sh" file & this will show the path of the script.sh file)

bash-3.2# grep "column" /home/script.sh       (It will search the "column" word in "script.sh" file this will not show the path)

bash-3.2# grep -r "LAST" /home/                     (It will search the "column" word in in the entire /home folder)

Search for the given string in a single file

Syn:   grep "literal_string" filename

grep 'word' filename

grep 'word' file1 file2 file3

grep 'string1 string2'  filename

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To see the environment variable for particular path:

   bash-3.2$ env |grep PS_SERVDIR

      O/P:   PS_SERVDIR=/home/psoft/CACHE

To search particular word in that file in unix

#grep -i "word you want to search" /home/psoft/smit.log--------------->It will search in smit.log file

Command to check the shared memory segment

ipcs –m | grep 0x741

Check whether shared memory segments are created again with following command.

ipcs -m | grep 0x741                 (with root user)

To know more information on grep and find commands

$ man find

$man grep

shutdown command examples :

Shutdown the system and turn the power off immediately

# shutdown -h now

Shutdown the system after 10 minutes

# shutdown -h +10

Reboot the system using shutdown command

# shutdown -r now

Force the filesystem check during reboot.

# shutdown -Fr now