ptx documentation from Francois

doc/textutils.texi

@@ -35,6 +35,7 @@ START-INFO-DIR-ENTRY
 * od: (textutils)od invocation.                 Dump files in octal, etc.
 * paste: (textutils)paste invocation.           Merge lines of files.
 * pr: (textutils)pr invocation.                 Paginate or columnate files.
+* ptx: (textutils)ptx invocation.               Produce permuted indexes.
 * sort: (textutils)sort invocation.             Sort text files.
 * split: (textutils)split invocation.           Split into fixed-size pieces.
 * sum: (textutils)sum invocation.               Print traditional checksum.
@@ -117,12 +118,89 @@ This manual documents version @value{VERSION} of the GNU text utilities.
 * Formatting file contents::           fmt pr fold
 * Output of parts of files::           head tail split csplit
 * Summarizing files::                  wc sum cksum md5sum
-* Operating on sorted files::          sort uniq comm
+* Operating on sorted files::   sort uniq comm ptx
 * Operating on fields within a line::  cut paste join
 * Operating on characters::            tr expand unexpand
 * Opening the software toolbox::       The software tools philosophy.
 * Index::                              General index.
+
+@detailmenu
+ --- The Detailed Node Listing ---
+
+Output of entire files
+
+* cat invocation::              Concatenate and write files.
+* tac invocation::              Concatenate and write files in reverse.
+* nl invocation::               Number lines and write files.
+* od invocation::               Write files in octal or other formats.
+
+Formatting file contents
+
+* fmt invocation::              Reformat paragraph text.
+* pr invocation::               Paginate or columnate files for printing.
+* fold invocation::             Wrap input lines to fit in specified width.
+
+Output of parts of files
+
+* head invocation::             Output the first part of files.
+* tail invocation::             Output the last part of files.
+* split invocation::            Split a file into fixed-size pieces.
+* csplit invocation::           Split a file into context-determined pieces.
+
+Summarizing files
+
+* wc invocation::               Print byte, word, and line counts.
+* sum invocation::              Print checksum and block counts.
+* cksum invocation::            Print CRC checksum and byte counts.
+* md5sum invocation::           Print or check message-digests.
+
+Operating on sorted files
+
+* sort invocation::             Sort text files.
+* uniq invocation::             Uniqify files.
+* comm invocation::             Compare two sorted files line by line.
+* ptx invocation::              Produce a permuted index of file contents.
+
+@code{ptx}: Produce permuted indexes
+
+* General options in ptx::      Options which affect general program behaviour.
+* Charset selection in ptx::    Underlying character set considerations.
+* Input processing in ptx::     Input fields, contexts, and keyword selection.
+* Output formatting in ptx::    Types of output format, and sizing the fields.
+* Compatibility in ptx::        The GNU extensions to @code{ptx}
+
+Operating on fields within a line
+
+* cut invocation::              Print selected parts of lines.
+* paste invocation::            Merge lines of files.
+* join invocation::             Join lines on a common field.
+
+Operating on characters
+
+* tr invocation::               Translate, squeeze, and/or delete characters.
+* expand invocation::           Convert tabs to spaces.
+* unexpand invocation::         Convert spaces to tabs.
+
+@code{tr}: Translate, squeeze, and/or delete characters
+
+* Character sets::              Specifying sets of characters.
+* Translating::                 Changing one characters to another.
+* Squeezing::                   Squeezing repeats and deleting.
+* Warnings in tr::              Warning messages.
+
+Opening the software toolbox
+
+* Toolbox introduction::        Toolbox introduction
+* I/O redirection::             I/O redirection
+* The who command::             The @code{who} command
+* The cut command::             The @code{cut} command
+* The sort command::            The @code{sort} command
+* The uniq command::            The @code{uniq} command
+* Putting the tools together::  Putting the tools together
+
+@end detailmenu
 @end menu
+
 @end ifinfo
 
 
@@ -872,10 +950,12 @@ The program accepts the following options.  Also see @ref{Common options}.
 
 @table @samp
 
-@item +@var{first_page}[@var{:last_page}]
-@opindex +@var{first_page}[@var{:last_page}]
+@item +@var{first_page}[:@var{last_page}]
+@itemx --pages=@var{first_page}[:@var{last_page}]
+@opindex +@var{first_page}[:@var{last_page}]
+@opindex --pages
 Begin printing with page @var{first_page} and stop with
-@var{last_page}. Missing @samp{:LAST_PAGE} implies end of file. While
+@var{last_page}. Missing @samp{:@var{last_page}} implies end of file. While
 estimating the number of skipped pages each form feed in the input file
 results in a new page. Page counting with and without
 @samp{+@var{first_page}} is identical. By default, it starts with the
@@ -883,7 +963,9 @@ first page of input file (not first page printed). Page numbering may be
 altered by @samp{-N} option.
 
 @item -@var{column}
+@itemx --columns=@var{column}
 @opindex -@var{column}
+@opindex --columns
 @cindex down columns
 With each single @var{file}, produce @var{column}-column output and
 print columns down. The column width is automatically estimated from
@@ -892,24 +974,32 @@ truncated. The number of lines in the columns on each page will be
 balanced. @samp{-@var{column}} may not be used with @samp{-m} option.
 
 @item -a
+@itemx --across
 @opindex -a
+@opindex --across
 @cindex across columns
 With each single @var{file}, print columns across rather than down.
 @var{column} must be greater than one.
 
 @item -c
+@itemx --show-control-chars
 @opindex -c
+@opindex --show-control-chars
 Print control characters using hat notation (e.g., @samp{^G}); print
 other unprintable characters in octal backslash notation.  By default,
 unprintable characters are not changed.
 
 @item -d
+@itemx --double-space
 @opindex -d
+@opindex --double-space
 @cindex double spacing
 Double space the output.
 
 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
+@itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
 @opindex -e
+@opindex --expand-tabs
 @cindex input tabs
 Expand tabs to spaces on input.  Optional argument @var{in-tabchar} is
 the input tab character (default is @key{TAB}).  Second optional
@@ -918,15 +1008,19 @@ is 8).
 
 @item -f
 @itemx -F
+@itemx --form-feed
 @opindex -F
 @opindex -f
+@opindex --form-feed
 Use a form feed instead of newlines to separate output pages. Default
 page length of 66 lines is not altered. But the number of lines of text
 per page changes from 56 to 63 lines.
 
 
 @item -h @var{HEADER}
+@itemx --header=@var{HEADER}
 @opindex -h
+@opindex --header
 Replace the file name in the header with the centered string
 @var{header}. Left-hand-side truncation (marked by a @samp{*}) may occur
 if the total header line @samp{yy-mm-dd HH:MM HEADER Page nnnn}
@@ -935,7 +1029,9 @@ header. Don't use @samp{-h""}. A space between the -h option and the
 argument is always peremptory.
 
 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
+@itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
 @opindex -i
+@opindex --output-tabs
 @cindex output tabs
 Replace spaces with tabs on output.  Optional argument @var{out-tabchar}
 is the output tab character (default is @key{TAB}).  Second optional
@@ -943,7 +1039,9 @@ argument @var{out-tabwidth} is the output tab character's width (default
 is 8).
 
 @item -j
+@itemx --join-lines
 @opindex -j
+@opindex --join-lines
 Merge lines of full length. Used together with the column options
 @samp{-@var{column}}, @samp{-a -@var{column}} or @samp{-m}. Turns off
 @samp{-w} line truncation; no column alignment used; may be used with
@@ -951,14 +1049,18 @@ Merge lines of full length. Used together with the column options
 
 
 @item -l @var{page_length}
+@itemx --length=@var{page_length}
 @opindex -l
+@opindex --length
 Set the page length to @var{page_length} (default 66) lines. If
 @var{page_length} is less than or equal 10 (and <= 3 with @samp{-f}),
 the headers and footers are omitted, and all form feeds set in input
 files are eliminated, as if the @samp{-T} option had been given.
 
 @item -m
+@itemx --merge
 @opindex -m
+@opindex --merge
 Merge and print all @var{file}s in parallel, one in each column. If a
 line is too long to fit in a column, it is truncated (but see
 @samp{-j}). @samp{-s[@var{separator}]} may be used. Empty pages in some
@@ -970,7 +1072,9 @@ line numbers. The default header becomes
 
 
 @item -n[@var{number-separator}[@var{digits}]]
+@itemx --number-lines[=@var{number-separator}[@var{digits}]]
 @opindex -n
+@opindex --number-lines
 Precede each column with a line number; with parallel @var{file}s
 (@samp{-m}), precede only each line with a line number. Optional argument
 @var{number-separator} is the character to print after each number
@@ -980,12 +1084,16 @@ first line of the input file (not with the first line printed, see
 @samp{-N}).
 
 @item -N @var{line_number}
+@itemx --first-line-number=@var{line_number}
 @opindex -N
+@opindex --first-line-number
 Start line counting with no. @var{line_number} at first line of first
 page printed.
 
 @item -o @var{n}
+@itemx --indent=@var{n}
 @opindex -o
+@opindex --indent
 @cindex indenting lines
 @cindex left margin
 Indent each line with @var{n} (default is zero) spaces wide, i.e., set
@@ -993,12 +1101,16 @@ the left margin.  The total page width is @var{n} plus the width set
 with the @samp{-w} option.
 
 @item -r
+@itemx --no-file-warnings
 @opindex -r
+@opindex --no-file-warnings
 Do not print a warning message when an argument @var{file} cannot be
 opened.  (The exit status will still be nonzero, however.)
 
 @item -s[@var{separator}]
+@itemx --separator[=@var{separator}]
 @opindex -s
+@opindex --separator
 Separate columns by a string @var{separator}. Don't use
 @samp{-s @var{separator}}, no space between flag and argument. If this
 option is omitted altogether, the default is @key{TAB} together with
@@ -1007,7 +1119,9 @@ option is omitted altogether, the default is @key{TAB} together with
 does not affect line truncation or column alignment.
 
 @item -t
+@itemx --omit-header
 @opindex -t
+@opindex --omit-header
 Do not print the usual header [and footer] on each page, and do not fill
 out the bottoms of pages (with blank lines or a form feed). No page
 structure is produced, but retain form feeds set in the input files. The
@@ -1017,16 +1131,22 @@ useful together with other options; e.g.: @samp{-t -e4}, expand
 Use of @samp{-t} overrides @samp{-h}.
 
 @item -T
+@itemx --omit-pagination
 @opindex -T
+@opindex --omit-pagination
 Do not print header [and footer]. In addition eliminate all form feeds
 set in the input files.
 
 @item -v
+@itemx --show-nonprinting
 @opindex -v
+@opindex --show-nonprinting
 Print unprintable characters in octal backslash notation.
 
 @item -w @var{page_width}
+@itemx --width=@var{page_width}
 @opindex -w
+@opindex --width
 Set the page width to @var{page_width} (default 72) characters.
 With/without @samp{-w}, header lines are always truncated to
 @var{page_width} characters. With @samp{-w}, text lines are truncated,
@@ -1738,6 +1858,7 @@ These commands work with (or produce) sorted files.
 * sort invocation::             Sort text files.
 * uniq invocation::             Uniqify files.
 * comm invocation::             Compare two sorted files line by line.
+* ptx invocation::
 @end menu
 
 
@@ -2188,6 +2309,469 @@ Upon normal completion @code{comm} produces an exit code of zero.
 If there is an error it exits with nonzero status.
 
 
+@node ptx invocation
+@section @code{ptx}: Produce permuted indexes
+
+@pindex ptx
+
+@code{ptx} reads a text file and essentially produces a permuted index, with
+each keyword in its context.  The calling sketch is either one of:
+
+@example
+ptx [@var{option} @dots{}] [@var{file} @dots{}]
+ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
+@end example
+
+The @samp{-G} (or its equivalent: @samp{--traditional}) option disables
+all GNU extensions and revert to traditional mode, thus introducing some
+limitations, and changes several of the program's default option values.
+When @samp{-G} is not specified, GNU extensions are always enabled.  GNU
+extensions to @code{ptx} are documented wherever appropriate in this
+document.  See @xref{Compatibility in ptx} for an explicit list of them.
+
+Individual options are explained in incoming sections.
+
+When GNU extensions are enabled, there may be zero, one or several
+@var{file} after the options.  If there is no @var{file}, the program
+reads the standard input.  If there is one or several @var{file}, 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 produces the permuted index onto the standard
+output.
+
+When GNU extensions are @emph{not} enabled, that is, when the program
+operates in traditional mode, there may be zero, one or two parameters
+besides the options.  If there is no parameters, the program reads the
+standard input and produces the permuted index onto the standard output.
+If there is only one parameter, it names the text @var{input} to be read
+instead of the standard input.  If two parameters are given, they give
+respectively the name of the @var{input} file to read and the name of
+the @var{output} file to produce.  @emph{Be very careful} to note that,
+in this case, the contents of file given by the second parameter is
+destroyed.  This behaviour is dictated only by System V @code{ptx}
+compatibility, because GNU Standards discourage output parameters not
+introduced by an option.
+
+Note that for @emph{any} file named as the value of an option or as an
+input text file, a single dash @kbd{-} 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.
+
+@menu
+* General options in ptx::      Options which affect general program behaviour.
+* Charset selection in ptx::    Underlying character set considerations.
+* Input processing in ptx::     Input fields, contexts, and keyword selection.
+* Output formatting in ptx::    Types of output format, and sizing the fields.
+* Compatibility in ptx::
+@end menu
+
+
+@node General options in ptx
+@subsection General options
+
+@table @code
+
+@item -C
+@itemx --copyright
+Prints a short note about the Copyright and copying conditions, then
+exit without further processing.
+
+@item -G
+@itemx --traditional
+As already explained, this option disables all GNU extensions to
+@code{ptx} and switch to traditional mode.
+
+@item --help
+Prints a short help on standard output, then exit without further
+processing.
+
+@item --version
+Prints the program verison on standard output, then exit without further
+processing.
+
+@end table
+
+
+@node Charset selection in ptx
+@subsection Charset selection
+
+As it is setup now, the program assumes that the input file is coded
+using 8-bit ISO 8859-1 code, also known as Latin-1 character set,
+@emph{unless} if it is compiled for MS-DOS, in which case it uses the
+character set of the IBM-PC.  (GNU @code{ptx} is not known to work on
+smaller MS-DOS machines anymore.)  Compared to 7-bit ASCII, the set of
+characters which are letters is then different, this fact alters the
+behaviour of regular expression matching.  Thus, the default regular
+expression for a keyword allows foreign or diacriticized letters.
+Keyword sorting, however, is still crude; it obeys the underlying
+character set ordering quite blindly.
+
+@table @code
+
+@item -f
+@itemx --ignore-case
+Fold lower case letters to upper case for sorting.
+
+@end table
+
+
+@node Input processing in ptx
+@subsection Word selection and input processing
+
+@table @code
+
+@item -b @var{file}
+@item --break-file=@var{file}
+
+This option is an alternative way to option @code{-W} for describing
+which characters make up words.  This option introduces the name of a
+file which contains a list of characters which can@emph{not} be part of
+one word, this file is called the @dfn{Break file}.  Any character which
+is not part of the Break file is a word constituent.  If both options
+@code{-b} and @code{-W} are specified, then @code{-W} has precedence and
+@code{-b} is ignored.
+
+When GNU extensions are enabled, the only way to avoid newline as a
+break character is to write all the break characters in the file with no
+newline at all, not even at the end of the file.  When GNU extensions
+are disabled, spaces, tabs and newlines are always considered as break
+characters even if not included in the Break file.
+
+@item -i @var{file}
+@itemx --ignore-file=@var{file}
+
+The file associated with this option contains a list of words which will
+never be taken as keywords in concordance output.  It is called the
+@dfn{Ignore file}.  The file contains exactly one word in each line; the
+end of line separation of words is not subject to the value of the
+@code{-S} option.
+
+There is a default Ignore file used by @code{ptx} when this option is
+not specified, usually found in @file{/usr/local/lib/eign} if this has
+not been changed at installation time.  If you want to deactivate the
+default Ignore file, specify @code{/dev/null} instead.
+
+@item -o @var{file}
+@itemx --only-file=@var{file}
+
+The file associated with this option contains a list of words which will
+be retained in concordance output, any word not mentioned in this file
+is ignored.  The file is called the @dfn{Only file}.  The file contains
+exactly one word in each line; the end of line separation of words is
+not subject to the value of the @code{-S} option.
+
+There is no default for the Only file.  In the case there are both an
+Only file and an Ignore file, a word will be subject to be a keyword
+only if it is given in the Only file and not given in the Ignore file.
+
+@item -r
+@itemx --references
+
+On each input line, the leading sequence of non white characters will be
+taken to be a reference that has the purpose of identifying this input
+line on the produced permuted index.  See @xref{Output formatting in ptx} for
+more information about reference production.  Using this option change
+the default value for option @code{-S}.
+
+Using this option, the program does not try very hard to remove
+references from contexts in output, but it succeeds in doing so
+@emph{when} the context ends exactly at the newline.  If option
+@code{-r} is used with @code{-S} default value, or when GNU extensions
+are disabled, this condition is always met and references are completely
+excluded from the output contexts.
+
+@item -S @var{regexp}
+@itemx --sentence-regexp=@var{regexp}
+
+This option selects which regular expression will describe the end of a
+line or the end of a sentence.  In fact, there is other distinction
+between end of lines or end of sentences than the effect of this regular
+expression, and input line boundaries have no special significance
+outside this option.  By default, when GNU extensions are enabled and if
+@code{-r} option is not used, end of sentences are used.  In this
+case, the precise @var{regex} is imported from GNU emacs:
+
+@example
+[.?!][]\"')@}]*\\($\\|\t\\|  \\)[ \t\n]*
+@end example
+
+Whenever GNU extensions are disabled or if @code{-r} option is used, end
+of lines are used; in this case, the default @var{regexp} is just:
+
+@example
+\n
+@end example
+
+Using an empty REGEXP is equivalent to completely disabling end of line or end
+of sentence recognition.  In this case, the whole file is considered to
+be a single big line or sentence.  The user might want to disallow all
+truncation flag generation as well, through option @code{-F ""}.
+@xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
+Manual}.
+
+When the keywords happen to be near the beginning of the input line or
+sentence, this often creates an unused area at the beginning of the
+output context line; when the keywords happen to be near the end of the
+input line or sentence, this often creates an unused area at the end of
+the output context line.  The program tries to fill those unused areas
+by wrapping around context in them; the tail of the input line or
+sentence is used to fill the unused area on the left of the output line;
+the head of the input line or sentence is used to fill the unused area
+on the right of the output line.
+
+As a matter of convenience to the user, many usual backslashed escape
+sequences, as found in the C language, are recognized and converted to
+the corresponding characters by @code{ptx} itself.
+
+@item -W @var{regexp}
+@itemx --word-regexp=@var{regexp}
+
+This option selects which regular expression will describe each keyword.
+By default, if GNU extensions are enabled, a word is a sequence of
+letters; the @var{regexp} used is @code{\w+}.  When GNU extensions are
+disabled, a word is by default anything which ends with a space, a tab
+or a newline; the @var{regexp} used is @code{[^ \t\n]+}.
+
+An empty REGEXP is equivalent to not using this option, letting the
+default dive in.  @xref{Regexps, , Syntax of Regular Expressions, emacs,
+The GNU Emacs Manual}.
+
+As a matter of convenience to the user, many usual backslashed escape
+sequences, as found in the C language, are recognized and converted to
+the corresponding characters by @code{ptx} itself.
+
+@end table
+
+
+@node Output formatting in ptx
+@subsection Output formatting
+
+Output format is mainly controlled by @code{-O} and @code{-T} options,
+described in the table below.  When neither @code{-O} nor @code{-T} is
+selected, and if GNU extensions are enabled, the program choose an
+output format suited for a dumb terminal.  Each keyword occurrence is
+output to the center of one line, surrounded by its left and right
+contexts.  Each field is properly justified, so the concordance output
+could readily be observed.  As a special feature, if automatic
+references are selected by option @code{-A} and are output before the
+left context, that is, if option @code{-R} is @emph{not} selected, then
+a colon is added after the reference; this nicely interfaces with GNU
+Emacs @code{next-error} processing.  In this default output format, each
+white space character, like newline and tab, is merely changed to
+exactly one space, with no special attempt to compress consecutive
+spaces.  This might change in the future.  Except for those white space
+characters, every other character of the underlying set of 256
+characters is transmitted verbatim.
+
+Output format is further controlled by the following options.
+
+@table @code
+
+@item -g @var{number}
+@itemx --gap-size=@var{number}
+
+Select the size of the minimum white gap between the fields on the output
+line.
+
+@item -w @var{number}
+@itemx --width=@var{number}
+
+Select the output maximum width of each final line.  If references are
+used, they are included or excluded from the output maximum width
+depending on the value of option @code{-R}.  If this option is not
+selected, that is, when references are output before the left context,
+the output maximum width takes into account the maximum length of all
+references.  If this options is selected, that is, when references are
+output after the right context, the output maximum width does not take
+into account the space taken by references, nor the gap that precedes
+them.
+
+@item -A
+@itemx --auto-reference
+
+Select automatic references.  Each input line will have an automatic
+reference made up of the file name and the line ordinal, with a single
+colon between them.  However, the file name will be empty when standard
+input is being read.  If both @code{-A} and @code{-r} are selected, then
+the input reference is still read and skipped, but the automatic
+reference is used at output time, overriding the input reference.
+
+@item -R
+@itemx --right-side-refs
+
+In default output format, when option @code{-R} is not used, any
+reference produced by the effect of options @code{-r} or @code{-A} are
+given to the far right of output lines, after the right context.  In
+default output format, when option @code{-R} is specified, references
+are rather given to the beginning of each output line, before the left
+context.  For any other output format, option @code{-R} is almost
+ignored, except for the fact that the width of references is @emph{not}
+taken into account in total output width given by @code{-w} whenever
+@code{-R} is selected.
+
+This option is automatically selected whenever GNU extensions are
+disabled.
+
+@item -F @var{string}
+@itemx --flac-truncation=@var{string}
+
+This option will request that any truncation in the output be reported
+using the string @var{string}.  Most output fields theoretically extend
+towards the beginning or the end of the current line, or current
+sentence, as selected with option @code{-S}.  But there is a maximum
+allowed output line width, changeable through option @code{-w}, which is
+further divided into space for various output fields.  When a field has
+to be truncated because cannot extend until the beginning or the end of
+the current line to fit in the, then a truncation occurs.  By default,
+the string used is a single slash, as in @code{-F /}.
+
+@var{string} may have more than one character, as in @code{-F ...}.
+Also, in the particular case @var{string} is empty (@code{-F ""}),
+truncation flagging is disabled, and no truncation marks are appended in
+this case.
+
+As a matter of convenience to the user, many usual backslashed escape
+sequences, as found in the C language, are recognized and converted to
+the corresponding characters by @code{ptx} itself.
+
+@item -M @var{string}
+@itemx --macro-name=@var{string}
+
+Select another @var{string} to be used instead of @samp{xx}, while
+generating output suitable for @code{nroff}, @code{troff} or @TeX{}.
+
+@item -O
+@itemx --format=roff
+
+Choose an output format suitable for @code{nroff} or @code{troff}
+processing.  Each output line will look like:
+
+@example
+.xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
+@end example
+
+so it will be possible to write an @samp{.xx} roff macro to take care of
+the output typesetting.  This is the default output format when GNU
+extensions are disabled.  Option @samp{-M} might be used to change
+@samp{xx} to another macro name.
+
+In this output format, each non-graphical character, like newline and
+tab, is merely changed to exactly one space, with no special attempt to
+compress consecutive spaces.  Each quote character: @kbd{"} is doubled
+so it will be correctly processed by @code{nroff} or @code{troff}.
+
+@item -T
+@itemx --format=tex
+
+Choose an output format suitable for @TeX{} processing.  Each output
+line will look like:
+
+@example
+\xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
+@end example
+
+@noindent
+so it will be possible to write write a @code{\xx} definition to take
+care of the output typesetting.  Note that when references are not being
+produced, that is, neither option @code{-A} nor option @code{-r} is
+selected, the last parameter of each @code{\xx} call is inhibited.
+Option @samp{-M} might be used to change @samp{xx} to another macro
+name.
+
+In this output format, some special characters, like @kbd{$}, @kbd{%},
+@kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
+backslash.  Curly brackets @kbd{@{}, @kbd{@}} are also protected with a
+backslash, but also enclosed in a pair of dollar signs to force
+mathematical mode.  The backslash itself produces the sequence
+@code{\backslash@{@}}.  Circumflex and tilde diacritics produce the
+sequence @code{^\@{ @}} and @code{~\@{ @}} respectively.  Other
+diacriticized characters of the underlying character set produce an
+appropriate @TeX{} sequence as far as possible.  The other non-graphical
+characters, like newline and tab, and all others characters which are
+not part of ASCII, are merely changed to exactly one space, with no
+special attempt to compress consecutive spaces.  Let me know how to
+improve this special character processing for @TeX{}.
+
+@end table
+
+
+@node Compatibility in ptx
+@subsection The GNU extensions to @code{ptx}
+
+This version of @code{ptx} contains a few features which do not exist in
+System V @code{ptx}.  These extra features are suppressed by using the
+@samp{-G} command line option, unless overridden by other command line
+options.  Some GNU extensions cannot be recovered by overriding, so the
+simple rule is to avoid @samp{-G} if you care about GNU extensions.
+Here are the differences between this program and System V @code{ptx}.
+
+@itemize @bullet
+
+@item
+This program can read many input files at once, it always writes the
+resulting concordance on standard output.  On the other end, System V
+@code{ptx} reads only one file and produce the result on standard output
+or, if a second @var{file} parameter is given on the command, to that
+@var{file}.
+
+Having output parameters not introduced by options is a quite dangerous
+practice which GNU avoids as far as possible.  So, for using @code{ptx}
+portably between GNU and System V, you should pay attention to always
+use it with a single input file, and always expect the result on
+standard output.  You might also want to automatically configure in a
+@samp{-G} option to @code{ptx} calls in products using @code{ptx}, if
+the configurator finds that the installed @code{ptx} accepts @samp{-G}.
+
+@item
+The only options available in System V @code{ptx} are options @samp{-b},
+@samp{-f}, @samp{-g}, @samp{-i}, @samp{-o}, @samp{-r}, @samp{-t} and
+@samp{-w}.  All other options are GNU extensions and are not repeated in
+this enumeration.  Moreover, some options have a slightly different
+meaning when GNU extensions are enabled, as explained below.
+
+@item
+By default, concordance output is not formatted for @code{troff} or
+@code{nroff}.  It is rather formatted for a dumb terminal.  @code{troff}
+or @code{nroff} output may still be selected through option @code{-O}.
+
+@item
+Unless @code{-R} option is used, the maximum reference width is
+subtracted from the total output line width.  With GNU extensions
+disabled, width of references is not taken into account in the output
+line width computations.
+
+@item
+All 256 characters, even @kbd{NUL}s, are always read and processed from
+input file with no adverse effect, even if GNU extensions are disabled.
+However, System V @code{ptx} does not accept 8-bit characters, a few
+control characters are rejected, and the tilda @kbd{~} is condemned.
+
+@item
+Input line length is only limited by available memory, even if GNU
+extensions are disabled.  However, System V @code{ptx} processes only
+the first 200 characters in each line.
+
+@item
+The break (non-word) characters default to be every character except all
+letters of the underlying character set, diacriticized or not.  When GNU
+extensions are disabled, the break characters default to space, tab and
+newline only.
+
+@item
+The program makes better use of output line width.  If GNU extensions
+are disabled, the program rather tries to imitate System V @code{ptx},
+but still, there are some slight disposition glitches this program does
+not completely reproduce.
+
+@item
+The user can specify both an Ignore file and an Only file.  This is not
+allowed with System V @code{ptx}.
+
+@end itemize
+
+
 @node Operating on fields within a line
 @chapter Operating on fields within a line
 
@@ -2845,7 +3429,6 @@ ones, to tabs.
 
 @end table
 
-
 @c              What's GNU?
 @c              Arnold Robbins
 @node Opening the software toolbox
@@ -2856,13 +3439,13 @@ number 2, in the @cite{What's GNU?} column. It was written by Arnold
 Robbins.
 
 @menu
-* Toolbox introduction::
-* I/O redirection::
-* The who command::
-* The cut command::
-* The sort command::
-* The uniq command::
-* Putting the tools together::
+* Toolbox introduction::        Toolbox introduction
+* I/O redirection::             I/O redirection
+* The who command::             The @code{who} command
+* The cut command::             The @code{cut} command
+* The sort command::            The @code{sort} command
+* The uniq command::            The @code{uniq} command
+* Putting the tools together::  Putting the tools together
 @end menu