(coreutils.info)Input processing in ptx

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7.5.3 Word selection and input processing
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‘-b FILE’
‘--break-file=FILE’

     This option provides an alternative (to ‘-W’) method of describing
     which characters make up words.  It introduces the name of a file
     which contains a list of characters which can_not_ be part of one
     word; this file is called the “Break file”.  Any character which is
     not part of the Break file is a word constituent.  If both options
     ‘-b’ and ‘-W’ are specified, then ‘-W’ has precedence and ‘-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.

‘-i FILE’
‘--ignore-file=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 “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 ‘-S’ option.

‘-o FILE’
‘--only-file=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 “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 ‘-S’ option.

     There is no default for the Only file.  When both an Only file and
     an Ignore file are specified, a word is considered a keyword only
     if it is listed in the Only file and not in the Ignore file.

‘-r’
‘--references’

     On each input line, the leading sequence of non-white space
     characters will be taken to be a reference that has the purpose of
     identifying this input line in the resulting permuted index.  Note:
     Output formatting in ptx, for more information about reference
     production.  Using this option changes the default value for option
     ‘-S’.

     Using this option, the program does not try very hard to remove
     references from contexts in output, but it succeeds in doing so
     _when_ the context ends exactly at the newline.  If option ‘-r’ is
     used with ‘-S’ default value, or when GNU extensions are disabled,
     this condition is always met and references are completely excluded
     from the output contexts.

‘-S REGEXP’
‘--sentence-regexp=REGEXP’

     This option selects which regular expression will describe the end
     of a line or the end of a sentence.  In fact, this regular
     expression is not the only distinction between end of lines or end
     of sentences, and input line boundaries have no special
     significance outside this option.  By default, when GNU extensions
     are enabled and if ‘-r’ option is not used, end of sentences are
     used.  In this case, this REGEX is imported from GNU Emacs:

          [.?!][]\"')}]*\\($\\|\t\\|  \\)[ \t\n]*

     Whenever GNU extensions are disabled or if ‘-r’ option is used, end
     of lines are used; in this case, the default REGEXP is just:

          \n

     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 ‘-F ""’.  *Note Syntax of Regular Expressions:
     (emacs)Regexps.

     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 from the C language are recognized and converted
     to the corresponding characters by ‘ptx’ itself.

‘-W REGEXP’
‘--word-regexp=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 REGEXP used is ‘\w+’.  When GNU extensions
     are disabled, a word is by default anything which ends with a
     space, a tab or a newline; the REGEXP used is ‘[^ \t\n]+’.

     An empty REGEXP is equivalent to not using this option.  Note:
     Syntax of Regular Expressions.

     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 ‘ptx’ itself.