ptx: Produce permuted indexes
ptx reads a text file and essentially produces a permuted index, with
each keyword in its context. The calling sketch is either one of:
ptx [option …] [file …] ptx -G [option …] [input [output]]
The -G (or its equivalent: --traditional) option disables
all GNU extensions and reverts to traditional mode, thus introducing some
limitations and changing several of the program’s default option values.
When -G is not specified, GNU extensions are always enabled.
GNU extensions to
ptx are documented wherever appropriate in this
document. See The GNU extensions to
ptx, for the full list.
Individual options are explained in the following sections.
When GNU extensions are enabled, there may be zero, one or several files after the options. If there is no file, the program reads the standard input. If there is one or several files, they give the name of input files which are all read in turn, as if all the input files were concatenated. However, there is a full contextual break between each file and, when automatic referencing is requested, file names and line numbers refer to individual text input files. In all cases, the program outputs the permuted index to the standard output.
When GNU extensions are not enabled, that is, when the program
operates in traditional mode, there may be zero, one or two parameters
besides the options. If there are no parameters, the program reads the
standard input and outputs the permuted index to the standard output.
If there is only one parameter, it names the text input to be read
instead of the standard input. If two parameters are given, they give
respectively the name of the input file to read and the name of
the output file to produce. Be very careful to note that,
in this case, the contents of file given by the second parameter is
destroyed. This behavior is dictated by System V
compatibility; GNU Standards normally discourage output parameters not
introduced by an option.
Note that for any file named as the value of an option or as an input text file, a single dash ‘-’ may be used, in which case standard input is assumed. However, it would not make sense to use this convention more than once per program invocation.