GAWK: Effective AWK Programming

Glossary 309Data DrivenA description of awk programs, where you specify the data you are interestedin processing, and what to do when that data is seen.Data ObjectsThese are numbers and strings of characters. Numbers are converted into stringsand vice versa, as needed. (See Section 5.4 [Conversion of Strings and Numbers],page 79.)DeadlockThe situation in which two communicating processes are each waiting for theother to perform an action.Double-PrecisionAn internal representation of numbers that can have fractional parts. Doubleprecisionnumbers keep track of more digits than do single-precision numbers,but operations on them are sometimes more expensive. This is the way awkstores numeric values. It is the C type double.Dynamic Regular ExpressionA dynamic regular expression is a regular expression written as an ordinaryexpression. It could be a string constant, such as "foo", but it may also be anexpression whose value can vary. (See Section 2.8 [Using Dynamic Regexps],page 34.)EnvironmentA collection of strings, of the form name=val, that each program has availableto it. Users generally place values into the environment in order to provide informationto various programs. Typical examples are the environment variablesHOME and PATH.Empty StringSee “Null String.”Epoch The date used as the “beginning of time” for timestamps. Time values inUnix systems are represented as seconds since the epoch, with library functionsavailable for converting these values into standard date and time formats.The epoch on Unix and POSIX systems is 1970-01-01 00:00:00 UTC. See also“GMT” and “UTC.”Escape SequencesA special sequence of characters used for describing nonprinting characters,such as ‘\n’ for newline or ‘\033’ for the ASCII ESC (Escape) character. (SeeSection 2.2 [Escape Sequences], page 25.)FDLFieldSee “Free Documentation License.”When awk reads an input record, it splits the record into pieces separated bywhitespace (or by a separator regexp that you can change by setting the builtinvariable FS). Such pieces are called fields. If the pieces are of fixed length,you can use the built-in variable FIELDWIDTHS to describe their lengths. (SeeSection 3.5 [Specifying How Fields Are Separated], page 43, and Section 3.6[Reading Fixed-Width Data], page 48.)