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Grep command in linux explained

Grep command used for search files and search pattern. (Find Text in Files).

grep command stands for “global regular expression print

grep [options] pattern [files]

Options Description

-c : counts the frequency only

-h : Display the matched lines, but do not display the filenames.

-i : case insensitive Ignores, case for matching

-l : filenames only.(imp)

-n : line number if word in a file

-v : lines that are not matched with the keyword

-e exp : Specifies expression with this option. Can use multiple times.

-f file : takes the file patterns

-E : Treats pattern as an extended regular expression (ERE)

-w : prints whole words in a file

-o : Print only matched words per line

Expressions

Start ^

End $

grep “^linux” mynewfile.txt

grep “ux$” mynewfile.txt

$grep –e “admin” –e “admin” –e “admin” newfile.txt

$grep –f newfile.txt mynewfile.txt

Finding a text in list of files in a directory.

grep ‘word’ file1 file2 file3

grep -n ‘root’ /etc/passwd

grep –color root /etc/passwd

cd /etc/nginx/sites-enabled
grep job.sarkari *

root@murali:/etc/nginx/sites-enabled# grep job.sarkari *
stories:server_name job.sarkariresultz.in;

searches only current directory

grep -rnw ‘/path/to/somewhere/’ -e ‘pattern’
-r or -R is recursive,
-n is line number, and
-w stands for match the whole word.
-l (lower-case L) can be added to just give the file name of matching files.
-e is the pattern used during the search
Along with these, –exclude, –include, –exclude-dir flags could be used for efficient searching:

Grep From Files and Display the File Name On Linux

grep -l “string” filenamegrep -l root /etc/*

Searching a String / word in files & directories

root@instance-1:/etc/nginx# grep -nr ‘cache-control’ .
./conf.d/global.config:62:add_header cache-control “max-age=31536000”;
./conf.d/expires.global:5:add_header cache-control: max-age=31536000;

grep command to search string word in file

root@-s-4vcpu-8gb-blr1-01:~# grep root /etc/passwd
root:x:0:0:root:/root:/bin/bash

grep WP_CACHE_KEY_SALT /var/www/html/yoursite.com/wp-config.php

all files containing string

grep -R containing text /home/user/

grep ‘string1 string2’ filename

finding a file containing a particular text string

grep “find me in home” /home/tom/*.txt

grep “find me anywhere in text files “~/*.txt

root@murali:~# grep “shivajobs.in” /etc/nginx/sites-enabled/*
/etc/nginx/sites-enabled/shivafile:server_name file.shivajobs.in;
/etc/nginx/sites-enabled/shivajobs.in:root /var/www/html/shivajobs.in/;
/etc/nginx/sites-enabled/shivajobs.in:server_name shivajobs.in www.shivajobs.in;
/etc/nginx/sites-enabled/shivajobs.in:include /var/www/html/shivajobs.in/nginx.conf;
/etc/nginx/sites-enabled/shivajobs.in: if ($host = shivajobs.in) {
/etc/nginx/sites-enabled/shivajobs.in:server_name shivajobs.in shivajobs.in;
root@murali:~#

use grep recursively

grep -R “192.168.0.1” /etc/

grep -R ‘string’ dir/

grep -R ‘expires’ /etc/nginx/

root@instance-1:/etc/nginx# grep -R ‘expires’ /etc/nginx/
/etc/nginx/rocket-nginx/default.conf: expires 30d;
/etc/nginx/rocket-nginx/default.conf: expires 30d;
/etc/nginx/rocket-nginx/default.conf: expires 30d;
/etc/nginx/rocket-nginx/rocket-nginx.tmpl: expires 30d;
/etc/nginx/rocket-nginx/rocket-nginx.tmpl: expires 30d;
/etc/nginx/rocket-nginx/rocket-nginx.tmpl: expires 30d;
/etc/nginx/sites-enabled/rajuginne: # Directives to send expires headers and turn off 404 error logging.
/etc/nginx/sites-enabled/rajuginne: expires 24h;
/etc/nginx/conf.d/default.conf: expires 31536000s;
/etc/nginx/conf.d/default.conf: expires 3600s;
/etc/nginx/conf.d/default.conf: expires 31536000s;
/etc/nginx/conf.d/headers.conf:#add_header expires $expires;
/etc/nginx/conf.d/headers.conf:map $sent_http_content_type $expires {
/etc/nginx/conf.d/browsercaching.confg: expires 3600s;
/etc/nginx/conf.d/expires.global: expires 365d;
/etc/nginx/conf.d/global2.config: expires max;

grep -R ‘add_header’ /etc/nginx/

grep -nr ‘ssl’ .

t@instance-1:/etc/nginx# grep -nr ‘ssl’ .
./nginx.conf:38: #ssl_protocols TLSv1 TLSv1.1 TLSv1.2; # Dropping SSLv3, ref: POODLE
./nginx.conf:39: #ssl_prefer_server_ciphers on;
./rocket-nginx/README.md:153:**<a name=’faq_ssl’>Will Rocket-Nginx work if my we bsite uses a SSL certificate (https) ?</a>**
./sites-enabled/f.in.conf:5:#ssl on;
./sites-enabled/ff.in.conf:6:ssl_certificate /etc/nginx/ssl/ssc.pem;
./sites-enabled/ff.in.conf:7:ssl_certificate_key /etc/nginx/ssl/ssc.key;
./sites-enabled/ffff.in:5:#listen 443 ssl http2;
./sites-enabled/.in:8:#include /etc/letsencrypt/options-ssl-nginx. conf;

The dot at the end searches the current directory. Meaning for each parameter:

-n Show relative line number in the file

‘yourString*’ String for search, followed by a wildcard character

-r Recursively search subdirectories listed

. Directory for search (current directory)

cd /etc/nginx/sites-enabled#

grep -nr ‘ssl’ .

./eaadharcard.co.in.conf:8: ssl on;

./eaadharcard.co.in.conf:9: ssl_certificate /etc/nginx/ssl/eaadharcard.co.in.pem;

./eaadharcard.co.in.conf:10: ssl_certificate_key /etc/nginx/ssl/eaadharcard.co.in.key;

./employmentnewsdaily.in:5: ssl on;

root@instance-1:~# grep . /proc/sys/net/ipv4/tcp*mem

/proc/sys/net/ipv4/tcp_mem:45525 60702 91050

/proc/sys/net/ipv4/tcp_rmem:4096 131072 6291456

/proc/sys/net/ipv4/tcp_wmem:4096 16384 4194304

root@instance-1:~#/etc/nginx/sites-enabled# grep -nr ‘raazkumar.com‘ .

linux find a file in a directory

The find command can only filter the directory hierarchy based on a file’s name and metadata. If you need to search based on the file’s content, use a tool like grep. Consider the following example:

find . -type f -exec grep “example” ‘{}’ \; -print

find command to find a file in a directory

find /path option filename

i want to ind newrelic.ini file this directory

find /etc/php/7.4/fpm/conf.d/ newrelic

ls -l /etc/php/7.4/fpm/conf.d/

2nd way

cd /etc/php/7.4/fpm/conf.d/

grep newrelic

/etc/php/7.4/fpm/conf.d

finding log errors with tail and grep command

tail -f /var/log/file.log | grep search_term

tail -f /var/log/nginx/error.log | grep 503

tail -f /www/test/error_log

tail -f www/test/error_log | grep 503

tail -f www/test/error_log | grep error

tail -f www/test/error_log | grep conn

As the output of grep is buffered, Add –line-buffered to grep, and that may reduce the delay for you. Very useful in some case

tail -f /path/to/log | grep --line-buffered 'X' | grep -v 'Y'

If your grep does not have the option, you can use stdbuf as an alternative:

tail -f /path/to/log | stdbuf -oL grep 'X' | grep -v 'Y'

Top 10 GREP Commands in linux to search files directory words strings