You can use grep to search for text inside files by specifying a search pattern and a file (or directory). The basic syntax is:

grep "search_term" file.txt

This command will look for the term "search_term" in the file called file.txt and print out any matching lines.

Here are some practical ways to use grep effectively depending on what you're trying to do.

Search for a word or phrase in a single file

If you want to find all occurrences of a specific word or phrase in a file, just type:

grep "error" log.txt

This will show every line in log.txt that contains the word "error".
By default, grep is case-sensitive. If you want to ignore case, add the -i option:

grep -i "error" log.txt

Now it will match both "error", "Error", and "ERROR".

Also, if you want to know which lines matched, along with their line numbers, use the -n flag:

grep -n "404" access.log

This helps when you're debugging logs or config files.

Search recursively through multiple files and directories

To search across all files in a directory and its subdirectories, use the -r (or --recursive) option:

grep -r "timeout" /var/www/

This will scan all files under /var/www/ for the word "timeout" and show the filename and matching line.

Combine this with --include to only search specific file types:

grep -r "function_name" . --include="*.php"

This searches only .php files in the current directory and below for the word "function_name".

Show more context around matches

Sometimes seeing just the matching line isn't enough. You can show a few lines before or after the match using:

• -A 2 – shows 2 lines after the match
• -B 2 – shows 2 lines before
• -C 2 – shows 2 lines before and after

For example:

grep -C 3 "database error" app.log

This gives you 3 lines of context around each match, making it easier to understand what's going on without opening the whole file.

Get only filenames that contain a match

If you don’t care about the actual matching line but just want to know which files contain a term, use -l:

grep -l "deprecated" *.js

This lists all .js files in the current directory that have the word "deprecated" somewhere in them.

It’s useful when scanning large codebases for certain keywords or patterns.

That’s basically how you use grep to search inside files. It's simple but powerful once you get used to the flags. You can chain options together too — like grep -rni to combine recursive search, case-insensitive matching, and line numbers.

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