Find Files Containing a String Pattern in Linux

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Grep is a powerful command line utility to search for files containing text string patterns in linux. In this tutorial we’ll be using grep with some common options to refine our file searches for better results.

The syntax for the grep command is as follows:

grep [options] "pattern" /files|directories/to/search

These are some useful and common options for the grep command:

• (-w) Only show matches containing whole words.
• (-i) Ignores upper/lower case distinction.
• (-l) Show the file names of files containing the matching string.
• (-s) Suppress error messages about nonexistent or unreadable files.
• (-o) Print only the matched part of a matching line.
• (-n) Print the line number containing the match.
• (-r) Read all files under a directory and its subdirectories recursively.
• (-R) Same as the (-r) option, but also follows symbolic links.
• (-h) Do not display the file name.

You can use one or more options to refine your search with grep.

Lets take a look at a few examples to find files containing a string pattern with grep.

Find Files Containing A String Pattern

To find a string (linux is awesome) within all text (.txt) files in a given directory you can use the following command in terminal:

grep "linux is awesome" /home/user/*.txt

To search in subdirectories you can use the (-r) option:

grep -r "linux is awesome" /home/user/*.txt

You can change the file extension to any type of text file you wish to search (.html, .md, .sh, or any other type).

Find Files With Case Insensitive Strings

Use the (-i) option to find case insensitive strings:

grep -i "LINUX is awesome" /home/user/*.txt

If you don’t know if the string you’re searching for is upper or lower case, then you will need to use this option.

Find Files With Specific Strings

To find files containing a specific string use the (-rnw) options:

grep -rnw "linux" /home/user/*.txt

Use grep In A Shell Script

grep is an excellent tool to use in shell scripts to automate complex searches.

In this example we’ll search for a string pattern and check if it repeats more than once in each file. If it repeats more than once, we’ll print the file names.

DIR=/home/user

for i in "$DIR"/*.txt; do
  if [ $(grep -ho 'my-search-pattern' $i | wc -l) -gt 1 ]; then
    echo $(basename $i)
  fi
done

As you can see we are piping the grep command to wc which counts how many times the pattern repeats. Then we use the echo command to print the file names of the files that have the pattern repeat more than once.

Conclusion

That was our brief look at the grep command to find files containing a text string pattern. You should now have a good understanding of how to use grep with some useful and common options.

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