To count the number of lines that contain a string or word using the grep command in Unix or Linux, you can use the -c or --count option.
For example, to count the number of lines in a file that contain the word "test," you can use the following command:
grep -c "test" file.txt
This will print the number of lines in the file file.txt that contain the word "test."
You can also use the -o or --only-matching option to print only the matching lines, and pipe the output to the wc command with the -l option to count the number of lines:
grep -o "test" file.txt | wc -l
This will also count the number of lines in the file file.txt that contain the word "test."