Grep searching two words in a line

"Both on the same line" means "'rice' followed by random characters followed by 'lemon' or the other way around".

In regex that is rice.*lemon or lemon.*rice. You can combine that using a |:

grep -E 'rice.*lemon|lemon.*rice' some_file

If you want to use normal regex instead of extended ones (-E) you need a backslash before the |:

grep 'rice.*lemon\|lemon.*rice' some_file

For more words that quickly gets a bit lengthy and it's usually easier to use multiple calls of grep, for example:

grep rice some_file | grep lemon | grep chicken

You can pipe the output of first grep command to another grep command and that would match both the patterns. So, you can do something like:

grep <first_pattern> <file_name> | grep <second_pattern>

or,

cat <file_name> | grep <first_pattern> | grep <second_pattern>

Example:

Let's add some contents to our file:

$ echo "This line contains lemon." > test_grep.txt
$ echo "This line contains rice." >> test_grep.txt
$ echo "This line contains both lemon and rice." >> test_grep.txt
$ echo "This line doesn't contain any of them." >> test_grep.txt
$ echo "This line also contains both rice and lemon." >> test_grep.txt

What does the file contain:

$ cat test_grep.txt 
This line contains lemon.
This line contains rice.
This line contains both lemon and rice.
This line doesn't contain any of them.
This line also contains both rice and lemon.

Now, let's grep what we want:

$ grep rice test_grep.txt | grep lemon
This line contains both lemon and rice.
This line also contains both rice and lemon.

We only get the lines where both the patterns match. You can extend this and pipe the output to another grep command for further "AND" matches.

Though the question asks for 'grep', I thought it might be helpful to post a simple 'awk' solution:

awk '/lemon/ && /rice/'

This can easily be extended with more words, or other boolean expressions besides 'and'.