Package io.jawk.ext

Class StdinExtension

java.lang.Object

io.jawk.ext.AbstractExtension

io.jawk.ext.StdinExtension

All Implemented Interfaces:

JawkExtension

public class StdinExtension
extends AbstractExtension
implements JawkExtension

Enable stdin processing in Jawk, to be used in conjunction with the -ni parameter. Since normal input processing is turned off via -ni, this is provided to enable a way to read input from stdin.

To use:

 StdinGetline() == 1 { print "--> " $0 }
 

The extension functions are as follows:

• StdinHasInput -
  Returns 1 when StdinGetline() does not block (i.e., when input is available or upon an EOF), 0 otherwise.
  Parameters:

  • none
  Returns:
  • 1 when StdinGetline() does not block, 0 otherwise.

• StdinGetline -
  Retrieve a line of input from stdin. The operation will block until input is available, EOF, or an IO error.
  Parameters:

  • none
  Returns:
  • 1 upon successful read of a line of input from stdin, 0 upon an EOF, and -1 when an IO error occurs.

• StdinBlock -
  Block until a call to StdinGetline() would not block.
  Parameters:

  • chained block function - optional
  Returns:
  • "Stdin" if this block object is triggered

Author:

Danny Daglas

Field Summary

Fields

Modifier and Type	Field	Description
static final StdinExtension	INSTANCE	Singleton extension instance backed by System.in.

Constructor Summary

Constructors

Constructor	Description
StdinExtension()	Creates a StdinExtension that reads from System.in.
StdinExtension(InputStream inputStream)	Creates a StdinExtension that reads from the specified input stream.

Method Summary

Modifier and Type	Method	Description
String	getExtensionName()	getExtensionName.
void	init(VariableManager vm, JRT jrt, AwkSettings settings)	Called after the creation and before normal processing of the extension, pass in the Jawk Runtime Manager and the Variable Manager once.
BlockObject	stdinBlockFunction(Object... args)	Returns a block object that waits for stdin readiness and optionally chains to another block.
Object	stdinGetlineFunction()	Reads the next line from stdin, or the AWK empty string at EOF.
int	stdinHasInputFunction()	Reports whether stdin data is available without blocking.

Methods inherited from class io.jawk.ext.AbstractExtension

getExtensionFunctions

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface io.jawk.ext.JawkExtension

getExtensionFunctions

Field Details

INSTANCE

public static final StdinExtension INSTANCE

Singleton extension instance backed by System.in.

Constructor Details

StdinExtension

public StdinExtension()

Creates a StdinExtension that reads from System.in.

StdinExtension

public StdinExtension(InputStream inputStream)

Creates a StdinExtension that reads from the specified input stream.

Parameters:

inputStream - the stream to read stdin data from

Method Details

init

public void init(VariableManager vm,
 JRT jrt,
 AwkSettings settings)

Called after the creation and before normal processing of the extension, pass in the Jawk Runtime Manager and the Variable Manager once.

It is guaranteed init() is called before invoke() is called.

Specified by:

init in interface JawkExtension

Overrides:

init in class AbstractExtension

Parameters:

vm - Reference to the Variable Manager

jrt - Reference to the Runtime

settings - Reference to the settings

getExtensionName

public String getExtensionName()

Description copied from class: AbstractExtension

getExtensionName.

Specified by:

getExtensionName in interface JawkExtension

Overrides:

getExtensionName in class AbstractExtension

Returns:

name of the extension package.

stdinHasInputFunction

public int stdinHasInputFunction()

Reports whether stdin data is available without blocking.

Returns:

1 when a read can proceed or EOF was reached, otherwise 0

stdinGetlineFunction

public Object stdinGetlineFunction()

Reads the next line from stdin, or the AWK empty string at EOF.

Returns:

Next line of input or an EOF marker compatible with the extension's contract

stdinBlockFunction

public BlockObject stdinBlockFunction(Object... args)

Returns a block object that waits for stdin readiness and optionally chains to another block.

Parameters:

args - Optional chaining block object

Returns:

Block object suitable for Jawk's block manager