Searching string in file linux

Finding a File Containing a Particular Text String In Linux Server

Tutorial details
Difficulty level	Easy
Root privileges	No
Requirements	grep
Est. reading time	Less than 2 minutes

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

grep command syntax for finding a file containing a particular text string

The syntax is:
grep » text string to search » directory-path
grep [option] » text string to search » directory-path
grep -r » text string to search «directory-path
grep -r -H » text string to search » directory-path
egrep -R » word-1|word-2 » /path/to/directory
egrep -w -R » word-1|word-2 » directory-path
Let us see some common example on how to use grep to search for strings in files.

How to search and find all files for a given text string

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»

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/
Look for all files containing cacheRoot text on Linux:
grep -R cacheRoot /home/vivek/

Trying to find all files containing specific text on my Linux desktop

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()’

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()’

Task: Search for two or more words

Use the egrep command as follows:
$ egrep -w -R ‘word1|word2’

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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()’

Task: Display matched text in color

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

Fig.01: grep command in action with colors and hiding the warnings on screen

Task: Ignore case

Our final example ignore case distinctions in both the search PATTERN and the input files:
grep -i -R ‘word’ /path/to/dir
grep -i -r ‘income tax’

How do I find all files containing specific text on Linux?

The syntax is:
egrep ‘pattern’ -rnw /path/to/dir/
egrep ‘word1|word2’ -rnw /home/vivek/backups/

Finding text strings within files using grep

In this example search for lines starting with any lowercase or uppercase letter:
grep «^[a-zA-Z]» -rns

• -r – Recursive search
• -R – Read all files under each directory, recursively. Follow all symbolic links, unlike -r grep option
• -n – Display line number of each matched line
• -s – Suppress error messages about nonexistent or unreadable files
• -w – Only work on words i.e. search only those lines containing matches that form whole words
• -l – Show the name of each input file when match found
• -i – Ignore case while searching

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Find and replace text within a file using commands

How can I find and replace specific words in a text file using command line?

7 Answers 7

• sed = Stream EDitor
• -i = in-place (i.e. save back to the original file)

The command string:

• s = the substitute command
• original = a regular expression describing the word to replace (or just the word itself)
• new = the text to replace it with
• g = global (i.e. replace all and not just the first occurrence)

file.txt = the file name

There’s multitude of ways to achieve it. Depending on the complexity of what one tries to achieve with string replacement, and depending on tools with which user is familiar, some methods may be preferred more than others.

In this answer I am using simple input.txt file, which you can use to test all examples provided here. The file contents:

Bash isn’t really meant for text processing, but simple substitutions can be done via parameter expansion , in particular here we can use simple structure $ .

This small script doesn’t do in-place replacement, meaning that you would have to save new text to new file, and get rid of the old file, or mv new.txt old.txt

Side note: if you’re curious about why while IFS= read -r ; do . done is used, it’s basically shell’s way of reading file line by line. See this for reference.

AWK, being a text processing utility, is quite appropriate for such task. It can do simple replacements and much more advanced ones based on regular expressions. It provides two functions: sub() and gsub() . The first one only replaces only the first occurrence, while the second — replaces occurrences in whole string. For instance, if we have string one potato two potato , this would be the result:

AWK can take an input file as argument, so doing same things with input.txt , would be easy:

Depending on the version of AWK you have, it may or may not have in-place editing, hence the usual practice is save and replace new text. For instance something like this:

Sed is a line editor. It also uses regular expressions, but for simple substitutions it’s sufficient to do:

What’s good about this tool is that it has in-place editing, which you can enable with -i flag.

Perl is another tool which is often used for text processing, but it’s a general purpose language, and is used in networking, system administration, desktop apps, and many other places. It borrowed a lot of concepts/features from other languages such as C,sed,awk, and others. Simple substitution can be done as so:

Like sed, perl also has the -i flag.

Python

This language is very versatile and is also used in a wide variety of applications. It has a lot of functions for working with strings, among which is replace() , so if you have variable like var=»Hello World» , you could do var.replace(«Hello»,»Good Morning»)

Simple way to read file and replace string in it would be as so:

With Python, however, you also need to output to new file , which you can also do from within the script itself. For instance, here’s a simple one:

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Finding a text string inside a file on a Linux server

By Adam
Post date

It never fails that I find myself hunting for a way to search for a particular text string in files. Usually I know the file, but often times I also find that I am completely unsure what file contains the string. Or while I am writting some code I need to find how many files use a certain function.

I know that using grep is the best way to search on a Linux server, so I start there. Here is the command syntax:

grep «text string to search for» /path/to/search

Examples
To search for a string called “myFunction” in all text files located in /var/www/html/*.php use:

grep «myFunction» /var/www/html/*.php

To search recursively in all sub-directories you would alter the command by adding the -r option:

grep -r «myFunction» /var/www/html

Now you have probably noticed that grep prints out the matching lines containing your string, but you may also need the filenames of the files containing the string instead. You can use the -H option to narrow the output the filename followed by the line containing your search string, like so:

grep -H -r «myFunction» /var/www/html

This would output something like:

. your_file.php: line containing myFunction ..

To print out just the filename you can cut command like this to clean the output further: (Note the one after the f, not an L)

grep -H -r «myFunction» /var/www/html | cut -d: -f1

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Searching string in file linux

The commands used are mainly grep and find.

Find string in file

grep string filename

grep name file.txt

Find string in file ignoring cases

grep string filename

grep -i name file.txt

Find string in current directory

grep string .

Find string recursively

grep -r string .

Find files that do not contain a string

grep -L string .

Find string recursively in only some specific files

grep string -r . —include=*.myextension

grep string -r . —include=*.

grep «name=Oscar» -r . —include=*.js

* if you specify —include it won’t look for the string in all files, just the ones included

Find string recursively in all files except the ones that contain certain extensions

grep string -r . —exclude=*.

grep «Serializable» -rl . —exclude=*.

Find string recursively all files including some extensions and excluding others

grep string -r . —include=*.myextension —exclude=*.myextension2

grep «my=string» -r . —include=*. —exclude=*.js

*It won’t look for the string in the js files.

Find string recursively in only some specific files and show their filename

grep string -rl . —include=*.myextension

grep «name=Oscar» -rl . —include=*.js

Find files and find a string in them using find

find . -name ‘*.extension’ -exec grep string +

find . -name ‘*.txt’ -exec grep Mytext <> +

find . -type f \( -name ‘*.htm’ -or -name ‘*.html’ \) -exec grep -i «mystring» <> +

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How to use sed to find and replace text in files in Linux / Unix shell

Find and replace text within a file using sed command

The procedure to change the text in files under Linux/Unix using sed:

1. Use Stream EDitor (sed) as follows:
2. sed -i ‘s/old-text/new-text/g’ input.txt
3. The s is the substitute command of sed for find and replace
4. It tells sed to find all occurrences of ‘old-text’ and replace with ‘new-text’ in a file named input.txt
5. Verify that file has been updated:
6. more input.txt

Let us see syntax and usage in details.

Tutorial details
Difficulty level	Easy
Root privileges	No
Requirements	sed utility on Linux, macOS or Unix-like OS
Est. reading time	4 minutes

Syntax: sed find and replace text

The syntax is:
sed ‘s/word1/word2/g’ input.file
## *bsd/macos sed syntax#
sed ‘s/word1/word2/g’ input.file > output.file
sed -i ‘s/word1/word2/g’ input.file
sed -i -e ‘s/word1/word2/g’ -e ‘s/xx/yy/g’ input.file
## use + separator instead of / ##
sed -i ‘s+regex+new-text+g’ file.txt
The above replace all occurrences of characters in word1 in the pattern space with the corresponding characters from word2.

Examples that use sed to find and replace

Let us create a text file called hello.txt as follows:
$ cat hello.txt
The is a test file created by nixCrft for demo purpose.
foo is good.
Foo is nice.
I love FOO.
I am going to use s/ for substitute the found expression foo with bar as follows:
sed ‘s/foo/bar/g’ hello.txt
Sample outputs:

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Please note that the BSD implementation of sed (FreeBSD/MacOS and co) does NOT support case-insensitive matching. You need to install gnu sed. Run the following command on Apple Mac OS:
$ brew install gnu-sed
######################################
### now use gsed command as follows ##
######################################
$ gsed -i ‘s/foo/bar/g I ‘ hello.txt
$ cat hello.txt

sed command problems

Consider the following text file:
$ cat input.txt
http:// is outdate.
Consider using https:// for all your needs.
Find word ‘http://’ and replace with ‘https://www.cyberciti.biz’:
sed ‘s/ http:// / https://www.cyberciti.biz /g’ input.txt
You will get an error that read as follows:

Our syntax is correct but the / delimiter character is also part of word1 and word2 in above example. Sed command allows you to change the delimiter / to something else. So I am going to use +:
sed ‘s+ http:// + https://www.cyberciti.biz +g’ input.txt
Sample outputs:

How to use sed to match word and perform find and replace

In this example only find word ‘love’ and replace it with ‘sick’ if line content a specific string such as FOO:
sed -i -e ‘/FOO/s/love/sick/’ input.txt
Use cat command to verify new changes:
cat input.txt

Recap and conclusion – Using sed to find and replace text in given files

The general syntax is as follows:
## find word1 and replace with word2 using sed ##
sed -i ‘s/word1/word2/g’ input
## you can change the delimiter to keep syntax simple ##
sed -i ‘s+word1+word2+g’ input
sed -i ‘s_word1_word2_g’ input
## you can add I option to GNU sed to case insensitive search ##
sed -i ‘s/word1/word2/gI’ input
sed -i ‘s_word1_word2_gI’ input

See BSD(used on macOS too) sed or GNU sed man page by typing the following command:
man sed

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