NAME
	gpp - Bash-based preprocessor for anything

SYNOPSIS
	gpp [-D name[=value]] [-f file | [-i input-file]
	    [-o output-file]] [-n count] [-s symbol] [-u [-u]]
	    [shell [argument] ...]

ETYMOLOGY
	gpp stands for General Preprocessor.

DESCRIPTION
	gpp lets a developer embed directives written in GNU
	Bash (this can be changed) into any text document.
	These directives are used to automate the writting of
	parts of the document.

	The preprocessing directives start with a symbol
	(or text string) specified by the developer. By default
	this symbol is @ (at).

	Any line starting with @< (where @ is the selected
	symbol for preprocessing directives) or @>, or is
	between a line starting with @< and a line starting
	with @>, is parsed as a line, written in Bash, that
	is executed during preprocessing.
	A @< line must have an associated @> line somewhere
	after it, all lines between them are parsed as
	preprocessing directives. A @> does however not need
	an associated @< line somewhere before it, making
	@> suitable for single line directives.

	Preprocessing directives can also be inline. For this,
	use @(COMMAND) where COMMAND is the Bash code to run.
	Additionally, gpp supports variable substitution.
	@{VARIABLE} will be replaces by the value if the
	variable (possibility environment variable) VARIABLE.
	gpp supports all modifiers thats Bash supports. For
	example, if you want the value to be included but
	uppercase you can write @{VARIABLE^^}, or @{VARIABLE,,}
	for lowercase.

	Everything that is not a preprocessing directive is
	echo verbatim.

OPTIONS
	-D name=value
		Set the environment variable name to hold
		the value value.

	-D name
		Set the environment variable name to hold
		the value 1.

	-f file
		Equivalent to -i FILE -o FILE.

	-i input-file
		Select file to process. Defaults to /dev/stdin.

	-n count
		Process the file recursively count times.
		Defaults to 1 time.

	-o output-file
		Select output file. Defaults to /dev/stdout.

	-s symbol
		Set the prefix symbol for preprocessor directives.
		Defaults to @.

	-u
		Clear the shebang line, remove it if this flag
		is used twice. If used twice, an empty line
		will be inserted after the new first line.

OPERANDS
	shell
		The shell to run instead of bash. The shell
		must be compatible with POSIX shell.

	argument ...
		Command line arguments for the shell.

EXAMPLES
    Conditional hello world
	This example only includes the "Hello world" line if
	the environment variable HELLO is defined and is not
	empty.

	@>if [ -z "$HELLO" ]; the
	Hello world
	@>fi

    Mutliline preprocessor directive
	This example creates the function uppercase() that
	convert lower case ASCII leters to uper case.

	@<uppercase () {
	     lower=qwertyuiopasdfghjklzxcvbnm
	     upper=QWERTYUIOPASDFGHJKLZXCVBNM
	     sed y/$lower/$upper/ <<<"$*"
	@>}

    Inline directives
	This example uses the uppercase() function above to
	convert the user's username to upper case. If the user's
	username is john, the code will expand to You are logged
	in as JOHN.

	You are logged in as @(uppercase $USER).

    Variable expansions
	In this example, if the user's username john, the code
	will expand to You are logged in as john.

	You are logged in as @{USER}.

    Variable expansion with substitution
	This example uses a substitution mechanism in Bash to
	convert the first letter in a variable to upper case.
	In this example, if the user's username john, the code
	will expand to You are logged in as John.

	You are logged in as @{USER^}.

RATIONALE
	Programmers need more automation when we write software
	and documentation. An unrestricted preprocessor lets
	you automate just about anything. Of course, it can be
	used for anything, must just writing software and
	documentation. Preprocessing can be used for more than
	automation, it can also be used to increase the flexibility
	of the work.

	C is one of the few languages that includes a preprocessor,
	some times it is not enough; and all languages need
	preprocessors.

SEE ALSO
	bash(1), jpp(1), cpp(1), env(1)