Which Linux command is used to search text or a specific file for lines that match a specific text string?

A) search
B) ls
C) apt-get
D) grep

The grep command is used to search text or a specific file for lines that match a specific text string. It is a powerful tool that can search recursively through directories, search for multiple patterns at once, and can even be used with regular expressions. The other options (search, ls, apt-get) do not have the same functionality as grep for searching text.