Using GNU sed:

$ sed -i '/pattern/d' ./file

To remove the lines and keep a copy of the original:

$ sed -i.bak '/pattern/d' ./file

Since the pattern is a regular expression, special characters should be escaped. For example, to remove all lines containing example.com:

$ sed -i '/example\.com/d' ./file

Documentation

• GNU sed manual – 2.2. Command-Line options
• GNU sed manual – 3.2. sed commands summary
• GNU sed manual – 5.3. Overview of basic regular expression syntax