Other Regular Expression Languages

 

One common set of UNIX utilities is that of grep/egrep/fgrep. Grep (Get Regular Expression and Print) uses something called basic regular expressions, egrep (Extended GREP) uses extended regular expressions and fgrep just looks for fixed strings. In the regular expression languages involved with these utilities (excepting fgrep), there are special symbols which represent:

• alphanumeric characters,
• alphabetic characters,
• control characters,
• numeric characters,
• graphic characters,
• lowercase letters,
• printable characters,
• punctuation characters,
• space characters,
• uppercase letters and
• hexadecimal (base 16) digits.

The negation (or inversion) operator for a list is not the ``!'', but rather the ``^ ''. The any single character match moves from ``?'' to ``.''. These regular expression languages also have special characters to represent the beginning or end of lines or words, ways of specifying how few or many (or both - a range in other words) of a match are allowed, choices between one pattern OR another.

Another regular expression language family belongs to the editors: ex/ed/vi. Other regular expression languages are found in languages such as awk, perl, .... The power behind the perl regular expression language is one reason for its use in CGI scripts, and the world wide web.