Linux Shell Scripting Cookbook - Third Edition

Treatment of special characters

Regular expressions use some characters, such as $, ^, ., *, +, {, and }, as special characters. But, what if we want to use these characters as normal text characters? Let's see an example of a regex, a.txt.

This will match the character a, followed by any character (due to the . character), which is then followed by the txt string. However, we want . to match a literal . instead of any character. In order to achieve this, we precede the character with a backward slash \ (doing this is called escaping the character). This indicates that the regex wants to match the literal character rather than its special meaning. Hence, the final regex becomes a\.txt.