Using grep to find string in files

Using grep to find string in files

How many times I had to search for something, let’s say my mac address, to change it in all files under /etc ? I couldn’t remebmer, different distros – different files, anyway, that’s an example, there are many out there, like searching log files, strings like IPs or titles and the worst part, recursively. I will show few examples of Using grep to find string in files and recursively too.

 

You need to use the grep command. The grep command searches the given input files for lines containing a match or a text string.

grep command syntax

The syntax is:

grep "text string to search” directory-path

OR

grep [option] "text string to search” directory-path

OR

grep -r "text string to search” directory-path

OR

grep -r -H "text string to search” directory-path

OR

egrep -R "word-1|word-2” directory-path

OR

egrep -w -R "word-1|word-2” directory-path

Examples

In this example, search for a string called ‘redeem reward’ in all text (*.txt) files located in /home/tom/ directory, use:
$ grep "redeem reward" /home/tom/*.txt
OR
$ grep "redeem reward" ~/*.txt

Task: Search all subdirectories recursively

You can search for a text string all files under each directory, recursively with -r option:
$ grep -r "redeem reward" /home/tom/
OR
$ grep -R "redeem reward" /home/tom/

Task: Only display filenames

By default, the grep command prints the matching lines. You can pass -H option to print the filename for each match:
$ grep -H -r "redeem reward" /home/tom
Sample outputs:

To just display the filename use the cut command as follows:
$ grep -H -R vivek /etc/* | cut -d: -f1
Sample outputs:

 

Task: Suppress file names

The grep command shows output on a separate line, and it is preceded by the name of the file in which it was found in the case of multiple files. You can pass the -h option to suppress inclusion of the file names in the output:
$ grep -h -R 'main()' ~/projects/*.c

Task: Display only words

You can select only those lines containing matches that form whole words using the -w option. In this example, search for word ‘getMyData()’ only in ~/projects/ dirctory:
$ grep -w -R 'getMyData()' ~/projects/

Task: Search for two or more words

Use the egrep command as follows:
$ egrep -w -R 'word1|word2' ~/projects/

Task: Hide warning spam

grep command generate error message as follows due to permission and other issues:

No such file or directory
No such device or address
Permission denied

To hide all errors or warning message spam generated by the grep command, append 2>/dev/null to grep command. This will send and hide unwanted output to /dev/null device:
$ grep -w -R 'getMyData()' ~/projects/ 2>/dev/null

Task: Display matched text in color

Pass the --color option to the grep command display matched text/words in color on the terminal:

 

Task: Ignore case (my favourite since the last grep update)

Our final example ignore case distinctions in both the search PATTERN and the input files:
grep -s -R 'word' /path/to/dir
grep -s -r 'income tax' ~/accounting/

 

or just

 

grep -sR ‘word’ /path/

 

0 (0)
Article Rating (No Votes)
Rate this article
Attachments
There are no attachments for this article.
Comments
There are no comments for this article. Be the first to post a comment.
Full Name
Email Address
Security Code Security Code
Related Articles RSS Feed
RHEL: Handling SCSI disks
Viewed 1025 times since Sun, May 27, 2018
How to enable automatic security updates on CentOS 7 with yum-cron
Viewed 430 times since Fri, Oct 26, 2018
How to find your System details using inxi
Viewed 1085 times since Sat, Jun 2, 2018
Stunnel Setup
Viewed 3076 times since Fri, Sep 28, 2018
HowTo: The Ultimate Logrotate Command Tutorial with 10 Examples
Viewed 830 times since Fri, Nov 30, 2018
Split and Reassemble files
Viewed 898 times since Mon, May 28, 2018
Kernel sysctl configuration file for Linux
Viewed 973 times since Fri, Aug 3, 2018
logrotate Understanding logrotate utility
Viewed 256 times since Sun, Jan 12, 2020
Understanding logrotate utility part 1
Viewed 463 times since Fri, Nov 30, 2018
RHCS6: ’fencing’ basics
Viewed 691 times since Sun, Jun 3, 2018