Examples are the editors vi and ed, the file searching commands grep, egrep and fgrep, awk, lex.
The popular pattern matching programming language Perl is also based on regular expressions. The arithmetic operators. If the hyphen appears right after the left bracket then it will be interpreted literally. Suppose, for example, that we wanted to select from a text file called mydata.txt all lines consisting of a single word made from the letters in abracadabra. We could use the following command.