CXL supports expressions for numeric computations and operations on strings. Any expression can be used as a pattern. If an expression evaluates to true (non-zero or non-null value) on the current input line, the line is matched and the associated action statements are executed.

Typical expression patterns involve comparisons between numbers or strings. A comparison expression uses a comparison operator. Comparison operators are discussed in the Comparison Expressions.

CXL supports string matching through regular expressions. A string matching pattern tests whether a string contains a substring matched by a regular expression.