org.unix4j.command

Interface Command<A extends Arguments<A>>

Type Parameters:

A - the type parameter defining the arguments and options of the command

All Known Implementing Classes:

AbstractCommand, AdHocCommand, CatCommand, CdCommand, CutCommand, EchoCommand, FindCommand, FromCommand, GrepCommand, HeadCommand, JoinedCommand, LsCommand, NoOp, SedCommand, SortCommand, TailCommand, UniqCommand, WcCommand, XargsCommand

public interface Command<A extends Arguments<A>>

A command is an executable unit defined by the command name and the command line arguments. To execute a command, execute(ExecutionContext, LineProcessor) is called which returns a LineProcessor object to perform the line-by-line command execution.

Commands can be joined to other commands which usually means that the first command's output forms the input of the second command.

Method Summary

Modifier and Type	Method and Description
LineProcessor	execute(ExecutionContext context, LineProcessor output) Executes this command and returns a LineProcessor object.
A	getArguments(ExecutionContext context) Returns the implementation specific command arguments and options for the given execution context.
String	getName() Returns the name of this command, usually a lower-case string such as "grep" or "ls".
Command<?>	join(Command<?> next) Returns a new command representing the combination of this command with next.
String	toString() Returns a string representation of the command instance including the argument and option values defined for the command.

Method Detail

getName

String getName()

Returns the name of this command, usually a lower-case string such as "grep" or "ls".

Returns:

the command name, usually a lower case string

getArguments

A getArguments(ExecutionContext context)

Returns the implementation specific command arguments and options for the given execution context. Note that the returned arguments instance may contain unresolved variables if variables have been passed to the command creation method. Variables can are resolved if they are defined in the VariableContext returned by the given context object. No variables are resolved if context is null.

Parameters:

context - the execution context with access to variables and value converters, or null if no variables should be resolved

Returns:

the arguments and options for this command

See Also:

Arguments.getForContext(ExecutionContext)

join

Command<?> join(Command<?> next)

Returns a new command representing the combination of this command with next. The returned command executes this command first and usually joins the output to the next command's input.

Note that some commands may use a slightly different interpretation of "joining a command". The xargs command for instance uses its joined command as target command; the values collected by xargs on its input stream are passed to the target command as arguments instead of as input.

Parameters:

next - the next command to join to this command

Returns:

a new command representing the combination of this command joined to next

execute

LineProcessor execute(ExecutionContext context,
                      LineProcessor output)

Executes this command and returns a LineProcessor object. Calling this method initiates the command execution, but the real processing of the command takes place when lines are passed to the returned LineProcessor object. The command execution is terminated by calling LineProcessor.finish().

The command writes its output to the specified output object. Depending on the command implementation, the output is written when lines are passed to the LineProcessor returned by this method, or when the execution terminates with the finish() call.

Parameters:

context - context object providing access to the current directory, environment variables and other information useful for the command during its execution

output - the output to write to

Returns:

true if another invocation with more input is expected, and false if this command has completed and no other invocation is required.

toString

String toString()

Returns a string representation of the command instance including the argument and option values defined for the command.

Overrides:

toString in class Object

Returns:

a string representation of the command including arguments and options, such as "grep -matchString myString -ignoreCase"