The GF Software System


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The GF software system implements the GF programming language. Its
components are
- the //compiler//, 
translating ``.gf`` source files to ``.gfo`` object files, to
``.pgf`` run-time grammars, and to various other formats
- the //run-time system//,
performing parsing, generation, translation and other functions with
``.pgf`` grammars
- the //command interpreter//, also known as the //GF shell//,
executing user commands by calling the compiler and the run-time system


This page describes the commands of the GF shell,
as well as the use of the compiler in batch mode.

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==The GF shell==

The GF shell is invoked by the command ``gf``, which takes arguments and
options according to the following syntax:
```
  gf (OPTION | FLAG)* FILE*
```
The shell maintains a  //state//, to which belong
- a multilingual PGF grammar
- optionally, a set of compiled GF modules (retaining ``oper`` definitions)
- a history of previous commands
- a set of string, tree, and command macros


Unless file arguments are provided to the ``gf`` command, the shell starts in an
empty state, with no grammars and no history. 

In the shell, a set of commands
is available. Some of these commands may change the grammars in the state. The general
syntax of commands is given by the following BNF grammar:
```
  COMMAND_LINE ::= COMMAND_PIPE
  COMMAND_LINE ::= COMMAND_PIPE ";" COMMAND_LINE
  COMMAND_PIPE ::= COMMAND
  COMMAND_PIPE ::= COMMAND "|" COMMAND_PIPE
  COMMAND      ::= COMMAND_ID (OPTION | FLAG)* ARGUMENT?
  OPTION       ::= "-"OPTION_ID
  FLAG         ::= "-"OPTION_ID "=" VALUE
  ARGUMENT     ::= QUOTED_STRING | TREE
  VALUE        ::= IDENT | QUOTED_STRING
```
A command pipe is a sequence of commands interpreted in such a way 
that the output of each command
is send as input to the next. The option ``-tr`` causes GF to show a trace,
i.e. the intermediate result of the command to which it is attached.

A command line is a sequence of pipes separated by ``;``. These pipes are
executed one by one, in the order of appearance.

===GF shell commands===

The full set of GF shell commands is listed below with explanations. 
This list can also be obtained in the GF shell by the command ``help -full``.

%!include: gf-help-full.txt

==The GF batch compiler==

With the option ``-batch``, GF can be invoked in batch mode, i.e.
without opening the shell, to compile files from ``.gf`` to ``.gfo``. 
The ``-s`` option ("silent") eliminates all messages except errors. 
```
  $ gf -batch -s LangIta.gf
```
With the option ``-make``, and as a set of
top-level grammar files (with the same abstract syntax) as arguments,
GF produces a ``.pgf`` file. The flag ``-optimize-pgf`` minimizes 
the size of the ``.pgf`` file, and is recommended for grammars to be shipped.
```
  $ gf -make -optimize-pgf LangIta.gf LangEng.gf LangGer.gf
```
The flag ``-output-format`` changes the output format from ``.pgf`` to
some other format. For instance
```
  $ gf -make -output-format=js LangEng.pgf LangGer.pgf
```
Notice that the arguments can be ``.pgf`` files, which in this case
are merged and written into a JavaScript grammar file.

More options and instructions are obtained with
```
  $ gf -help
```
To run GF from a //script//, redirection of standard input can be used:
```
  $ gf <script.gfs
```
The file ``script.gfs`` should then contain a sequence of GF commands, one per line.
Unrecognized command lines are skipped without terminating GF.


