Chapter 9. Input/Output Processing

Revision History
Revision V6.1-000	28 August 2014	Added information about using LOCAL sockets in “ZDELAY”, “ZBFSIZE”, “LISTEN”, “Close”, “CONNECT”. Improved the documentation of SOCKET devices in “WRITE Command”. Added the downloadable sockexamplemulti3.m example in “Socket Device Examples”. In “Document Conventions”, added the mnemonics for SOC(LOCAL) and SOC(TCP) for LOCAL and TCP sockets. In FIFO Characteristics, added a note about FIFO access permissions.
Revision V6.0-003	24 February 2014	Added the descriptions of [NO]FOLLOW and [NO]EMPT[ERM] deviceparameters of OPEN and USE. Improved the descriptions of “STREAM” and “FIXED”. In “CONNECT”, added information about IPv6 support. In “Writing Binary Files”, improved the example for performing a binary copy. Under Using Sequential Files, added a new section called “READ / WRITE Operations”. Improved the descriptions of “WRAP” and “FIXED”.
Revision V6.0-001	21 March 2013	In “EXCEPTION”, added a note about the handling of non-fatal errors.
Revision V6.0-000	19 November 2012	In “PIPE Characteristics”, improved the description of WRITE /EOF. In “Using Null Devices”, added information about /dev/zero, /dev/random, and /dev/urandom devices.
Revision V5.5-000/1	05 October 2012	In “ FIFO Characteristics” and “PIPE Characteristics”, added information about gtm_non_blocked_write_retries. Added the “Line Terminators ” section.
Revision V5.5-000	20 May 2012	In Section : “ FIFO Characteristics”, corrected the description of FIFO behavior with WRITEs.
Revision V5.4-002B	26 December 2011	Conversion to documentation revision history reflecting GT.M releases with revision history for each chapter.

Contents

I/O Intrinsic Special Variables

Device Name Variables
Cursor Position Variables
Status Variables

I/O Devices

I/O Device Recognition
Device Specification Defaults
How I/O Device parameters Work
Abbreviating Deviceparameters
Document Conventions
Device-Independent Programming

Using Terminals

Setting Terminal Characteristics
Logical Records for Terminals
READ * Command for Terminals
READ X#maxlen Command for Terminals
Terminal Deviceparameter Summary
Terminal Examples

Using Sequential Files

Setting Sequential File Characteristics
Sequential File Pointers
Line Terminators
READ / WRITE Operations
Writing Binary Files
Sequential File Deviceparameter Summary
Sequential File Examples

FIFO Characteristics

Considerations in Implementing FIFOs
Error Handling for FIFOs
GT.M Recognition of FIFOs
FIFO Device Examples
FIFO Deviceparameter Summary

Using Null Devices

Null Deviceparameter Summary
Null Device Examples

Using PIPE Devices

Modes of PIPE Operation
PIPE Characteristics
PIPE Device Examples
PIPE Deviceparameter Summary

Using Socket Devices

Message Management
Socket Read Operation
Socket Read Termination Conditions
Message Delimiters
Read Command
WRITE Command
Socket Device Operation
Socket Deviceparameter Summary
Socket Device Examples

I/O Commands

Open
Use
READ
Write
WRITE *
Close
Deviceparameter Summary Table

This chapter describes the following topics which relate to input and output processing:

Input/Output Intrinsic Special Variables, and their Maintenance.
GT.M provides several intrinsic special variables that allow processes to examine, and in some cases change, certain aspects of the input/output (I/O) processing. The focus in this chapter is how GT.M handles the standard ones, such as $IO, $X, $Y, and those that are GT.M-specific (for example, $ZA, $ZB).
Input/Output Devices
Each device type supported by GT.M responds to a particular subset of deviceparameters, while ignoring others. Devices may be programmed in a device-specific manner, or in a device-independent manner. This chapter discusses each device type, and provides tables of their deviceparameters.
Input/Output Commands and their Deviceparameters
GT.M bases its I/O processing on a simple character stream model. GT.M does not use any pre-declared formats. This chapter describes the GT.M I/O commands OPEN, USE, READ, WRITE, and CLOSE.

OPEN, USE, and CLOSE commands accept deviceparameters, which are keywords that permit a GT.M program to control the device state. Some deviceparameters require arguments. The current ANSI standard for GT.M does not define the deviceparameters for all devices. This chapter includes descriptions of the GT.M deviceparameters in the sections describing each command.

	Note
	The term "device" can refer to an entity manipulated by application code using Open, Use, Close, Read and Write commands as well as a device from the perspective of the operating system. We endeavor herein to always make it clear from the context which meaning is intended.

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