Recently, I have been solving some CTF questions, and I came across one that says, 'You have a bunch of files(approx 9090 files), and each contains some information. One of the files contains the flag you need, but it's impossible to open and check each file'.

In this case we can use greap command, let's see how...

Grep is command-line utility(not exactly a tool).

The grep command is a crucial tool for anyone working with text-based data and is highly efficient for tasks that require searching and processing large amounts of text.

1. Search in a Single File.

If you suspect the flag is in a specific file, you can use the following command

grep -i "picoCTF{" filename.txt

2.Search in All Files in the Current Directory.

If you want to search through all files in the current directory and its subdirectories

grep -r "picoCTF{" .

3.Search in All Files in a Directory.

If you are not sure where the flag is located but you know it is within a directory, use this command to search through all files

grep -r "picoCTF{" /path/to/directory/

4. Display Line Numbers.

The -n option displays the line numbers where the pattern is found

grep -n "pattern" filename

5. Search for Multiple Patterns.

You can search for multiple patterns by using the -e option.
bash

grep -e "pattern1" -e "pattern2" filename

6. Count the Number of Matches.

The -c option counts the number of lines that match the pattern.
bash

grep -c "pattern" filename

7. Search for the Flag Across Multiple Directories or Files.

If you know the flag might be in multiple files or directories, you can combine the directories in the command like this:

grep -r "picoCTF{" dir1/ dir2/ dir3/