Using sed to remove lines from a txt file <p>I have a big text file from which I want to remove some lines that are in another text file. It seems that the <code>sed</code> command in Unix shell is a good way to do this. However, I haven't been able to figure out which flags to use for this. .</p> <p>database.txt:</p> <pre><code>this is line 1 this is line 2 this is line 3 this is line 4 this is line 5 </code></pre> <p>lines_to_remove.txt</p> <pre><code>this is line 1 this is line 3 </code></pre> <p>what_i_want.txt</p> <pre><code>this is line 2 this is line 4 this is line 5 </code></pre>