GNU text utilities - 7. Operating on sorted files

Go to the first, previous, next, last section, table of contents.

# 7. Operating on sorted files

These commands work with (or produce) sorted files.

## 7.1 `sort`: Sort text files

`sort` sorts, merges, or compares all the lines from the given files, or standard input if none are given or for a file of ``-'`. By default, `sort` writes the results to standard output. Synopsis:

    sort [option]... [file]...

`sort` has three modes of operation: sort (the default), merge, and check for sortedness. The following options change the operation mode:

``-c'`
  Check whether the given files are already sorted: if they are not all sorted, print an error message and exit with a status of 1. Otherwise, exit successfully.
``-m'`
  Merge the given files by sorting them as a group. Each input file must always be individually sorted. It always works to sort instead of merge; merging is provided because it is faster, in the case where it works.

A pair of lines is compared as follows: if any key fields have been specified, `sort` compares each pair of fields, in the order specified on the command line, according to the associated ordering options, until a difference is found or no fields are left. Unless otherwise specified, all comparisons use the character collating sequence specified by the @env{LC_COLLATE} locale.

If any of the global options ``Mbdfinr'` are given but no key fields are specified, `sort` compares the entire lines according to the global options.

Finally, as a last resort when all keys compare equal (or if no ordering options were specified at all), `sort` compares the entire lines. The last resort comparison honors the ``-r'` global option. The ``-s'` (stable) option disables this last-resort comparison so that lines in which all fields compare equal are left in their original relative order. If no fields or global options are specified, ``-s'` has no effect.

GNU `sort` (as specified for all GNU utilities) has no limits on input line length or restrictions on bytes allowed within lines. In addition, if the final byte of an input file is not a newline, GNU `sort` silently supplies one. A line's trailing newline is part of the line for comparison purposes; for example, with no options in an ASCII locale, a line starting with a tab sorts before an empty line because tab precedes newline in the ASCII collating sequence.

Upon any error, `sort` exits with a status of ``2'`.

If the environment variable @env{TMPDIR} is set, `sort` uses its value as the directory for temporary files instead of ``/tmp'`. The ``-T tempdir'` option in turn overrides the environment variable.

The following options affect the ordering of output lines. They may be specified globally or as part of a specific key field. If no key fields are specified, global options apply to comparison of entire lines; otherwise the global options are inherited by key fields that do not specify any special options of their own. The ``-b'`, ``-d'`, ``-f'` and ``-i'` options classify characters according to the @env{LC_CTYPE} locale.

``-b'`
  Ignore leading blanks when finding sort keys in each line.
``-d'`
  Sort in phone directory order: ignore all characters except letters, digits and blanks when sorting.
``-f'`
  Fold lowercase characters into the equivalent uppercase characters when sorting so that, for example, ``b'` and ``B'` sort as equal.
``-g'`
  Sort numerically, using the standard C function `strtod` to convert a prefix of each line to a double-precision floating point number. This allows floating point numbers to be specified in scientific notation, like `1.0e-34` and `10e100`. Do not report overflow, underflow, or conversion errors. Use the following collating sequence:
  - Lines that do not start with numbers (all considered to be equal).
  - NaNs ("Not a Number" values, in IEEE floating point arithmetic) in a consistent but machine-dependent order.
  - Minus infinity.
  - Finite numbers in ascending numeric order (with -0 and +0 equal).
  - Plus infinity.
  Use this option only if there is no alternative; it is much slower than ``-n'` and it can lose information when converting to floating point.
``-i'`
  Ignore unprintable characters.
``-M'`
  An initial string, consisting of any amount of whitespace, followed by a month name abbreviation, is folded to UPPER case and compared in the order ``JAN'` < ``FEB'` < ... < ``DEC'`. Invalid names compare low to valid names. The @env{LC_TIME} locale determines the month spellings.
``-n'`
  Sort numerically: the number begins each line; specifically, it consists of optional whitespace, an optional ``-'` sign, and zero or more digits possibly separated by thousands separators, optionally followed by a radix character and zero or more digits. The @env{LC_NUMERIC} locale specifies the radix character and thousands separator. `sort -n` uses what might be considered an unconventional method to compare strings representing floating point numbers. Rather than first converting each string to the C `double` type and then comparing those values, sort aligns the radix characters in the two strings and compares the strings a character at a time. One benefit of using this approach is its speed. In practice this is much more efficient than performing the two corresponding string-to-double (or even string-to-integer) conversions and then comparing doubles. In addition, there is no corresponding loss of precision. Converting each string to `double` before comparison would limit precision to about 16 digits on most systems. Neither a leading ``+'` nor exponential notation is recognized. To compare such strings numerically, use the ``-g'` option.
``-r'`
  Reverse the result of comparison, so that lines with greater key values appear earlier in the output instead of later.

Other options are:

``-o output-file'`
  Write output to output-file instead of standard output. If output-file is one of the input files, `sort` copies it to a temporary file before sorting and writing the output to output-file.
``-t separator'`
  Use character separator as the field separator when finding the sort keys in each line. By default, fields are separated by the empty string between a non-whitespace character and a whitespace character. That is, given the input line `` foo bar'`, `sort` breaks it into fields `` foo'` and `` bar'`. The field separator is not considered to be part of either the field preceding or the field following.
``-u'`
  For the default case or the ``-m'` option, only output the first of a sequence of lines that compare equal. For the ``-c'` option, check that no pair of consecutive lines compares equal.
``-k pos1[,pos2]'`
  The recommended, POSIX, option for specifying a sort field. The field consists of the part of the line between pos1 and pos2 (or the end of the line, if pos2 is omitted), inclusive. Fields and character positions are numbered starting with 1. So to sort on the second field, you'd use ``-k 2,2'` See below for more examples.
``-z'`
  Treat the input as a set of lines, each terminated by a zero byte (ASCII NUL (Null) character) instead of an ASCII LF (Line Feed). This option can be useful in conjunction with ``perl -0'` or ``find -print0'` and ``xargs -0'` which do the same in order to reliably handle arbitrary pathnames (even those which contain Line Feed characters.)
``+pos1[-pos2]'`
  The obsolete, traditional option for specifying a sort field. The field consists of the line between pos1 and up to but not including pos2 (or the end of the line if pos2 is omitted). Fields and character positions are numbered starting with 0. See below.

In addition, when GNU `sort` is invoked with exactly one argument, options ``--help'` and ``--version'` are recognized. See section 2. Common options.

Historical (BSD and System V) implementations of `sort` have differed in their interpretation of some options, particularly ``-b'`, ``-f'`, and ``-n'`. GNU sort follows the POSIX behavior, which is usually (but not always!) like the System V behavior. According to POSIX, ``-n'` no longer implies ``-b'`. For consistency, ``-M'` has been changed in the same way. This may affect the meaning of character positions in field specifications in obscure cases. The only fix is to add an explicit ``-b'`.

A position in a sort field specified with the ``-k'` or ``+'` option has the form ``f.c'`, where f is the number of the field to use and c is the number of the first character from the beginning of the field (for ``+pos'`) or from the end of the previous field (for ``-pos'`). If the ``.c'` is omitted, it is taken to be the first character in the field. If the ``-b'` option was specified, the ``.c'` part of a field specification is counted from the first nonblank character of the field (for ``+pos'`) or from the first nonblank character following the previous field (for ``-pos'`).

A sort key option may also have any of the option letters ``Mbdfinr'` appended to it, in which case the global ordering options are not used for that particular field. The ``-b'` option may be independently attached to either or both of the ``+pos'` and ``-pos'` parts of a field specification, and if it is inherited from the global options it will be attached to both. Keys may span multiple fields.

Here are some examples to illustrate various combinations of options. In them, the POSIX ``-k'` option is used to specify sort keys rather than the obsolete ``+pos1-pos2'` syntax.

- Sort in descending (reverse) numeric order.

      sort -nr

  Sort alphabetically, omitting the first and second fields. This uses a single key composed of the characters beginning at the start of field three and extending to the end of each line.

      sort -k3

- Sort numerically on the second field and resolve ties by sorting alphabetically on the third and fourth characters of field five. Use ``:'` as the field delimiter.

      sort -t : -k 2,2n -k 5.3,5.4

  Note that if you had written ``-k 2'` instead of ``-k 2,2'` ``sort'` would have used all characters beginning in the second field and extending to the end of the line as the primary numeric key. For the large majority of applications, treating keys spanning more than one field as numeric will not do what you expect. Also note that the ``n'` modifier was applied to the field-end specifier for the first key. It would have been equivalent to specify ``-k 2n,2'` or ``-k 2n,2n'`. All modifiers except ``b'` apply to the associated field, regardless of whether the modifier character is attached to the field-start and/or the field-end part of the key specifier.
- Sort the password file on the fifth field and ignore any leading white space. Sort lines with equal values in field five on the numeric user ID in field three.

      sort -t : -k 5b,5 -k 3,3n /etc/passwd

  An alternative is to use the global numeric modifier ``-n'`.

      sort -t : -n -k 5b,5 -k 3,3 /etc/passwd

- Generate a tags file in case insensitive sorted order.

      find src -type f -print0 | sort -t / -z -f | xargs -0 etags --append

  The use of ``-print0'`, ``-z'`, and ``-0'` in this case mean that pathnames that contain Line Feed characters will not get broken up by the sort operation. Finally, to ignore both leading and trailing white space, you could have applied the ``b'` modifier to the field-end specifier for the first key,

      sort -t : -n -k 5b,5b -k 3,3 /etc/passwd

  or by using the global ``-b'` modifier instead of ``-n'` and an explicit ``n'` with the second key specifier.

      sort -t : -b -k 5,5 -k 3,3n /etc/passwd

## 7.2 `uniq`: Uniquify files

`uniq` writes the unique lines in the given ``input'`, or standard input if nothing is given or for an input name of ``-'`. Synopsis:

    uniq [option]... [input [output]]

By default, `uniq` prints the unique lines in a sorted file, i.e., discards all but one of identical successive lines. Optionally, it can instead show only lines that appear exactly once, or lines that appear more than once.

The input must be sorted. If your input is not sorted, perhaps you want to use `sort -u`.

If no output file is specified, `uniq` writes to standard output.

The program accepts the following options. Also see section 2. Common options.

``-n'`
``-f n'`
``--skip-fields=n'`
  Skip n fields on each line before checking for uniqueness. Fields are sequences of non-space non-tab characters that are separated from each other by at least one spaces or tabs.
``+n'`
``-s n'`
``--skip-chars=n'`
  Skip n characters before checking for uniqueness. If you use both the field and character skipping options, fields are skipped over first.
``-c'`
``--count'`
  Print the number of times each line occurred along with the line.
``-i'`
``--ignore-case'`
  Ignore differences in case when comparing lines.
``-d'`
``--repeated'`
  Print only duplicate lines.
``-D'`
``--all-repeated'`
  Print all duplicate lines and only duplicate lines. This option is useful mainly in conjunction with other options e.g., to ignore case or to compare only selected fields. This is a GNU extension.
``-u'`
``--unique'`
  Print only unique lines.
``-w n'`
``--check-chars=n'`
  Compare n characters on each line (after skipping any specified fields and characters). By default the entire rest of the lines are compared.

## 7.3 `comm`: Compare two sorted files line by line

`comm` writes to standard output lines that are common, and lines that are unique, to two input files; a file name of ``-'` means standard input. Synopsis:

    comm [option]... file1 file2

Before `comm` can be used, the input files must be sorted using the collating sequence specified by the @env{LC_COLLATE} locale, with trailing newlines significant. If an input file ends in a non-newline character, a newline is silently appended. The `sort` command with no options always outputs a file that is suitable input to `comm`.

With no options, `comm` produces three column output. Column one contains lines unique to file1, column two contains lines unique to file2, and column three contains lines common to both files. Columns are separated by a single TAB character.

The options ``-1'`, ``-2'`, and ``-3'` suppress printing of the corresponding columns. Also see section 2. Common options.

Unlike some other comparison utilities, `comm` has an exit status that does not depend on the result of the comparison. Upon normal completion `comm` produces an exit code of zero. If there is an error it exits with nonzero status.

## 7.4 `tsort`: Topological sort

`tsort` performs a topological sort on the given file, or standard input if no input file is given or for a file of ``-'`. Synopsis:

    tsort [option] [file]

`tsort` reads its input as pairs of strings, separated by blanks, indicating a partial ordering. The output is a total ordering that corresponds to the given partial ordering.

For example

    tsort <<EOF
    a b c
    d
    e f
    b c d e
    EOF

will produce the output

    a
    b
    c
    d
    e
    f

`tsort` will detect cycles in the input and writes the first cycle encountered to standard error.

Note that for a given partial ordering, generally there is no unique total ordering.

The only options are ``--help'` and ``--version'`. See section 2. Common options.

## 7.5 `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 revert to traditional mode, thus introducing some limitations, and changes 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. For the full list, see See section 7.5.5 The GNU extensions to `ptx`.

Individual options are explained in incoming sections.

When GNU extensions are enabled, there may be zero, one or several file after the options. If there is no file, the program reads the standard input. If there is one or several 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 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 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 behaviour is dictated only by System V `ptx` compatibility, because GNU Standards 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.

### 7.5.1 General options

``-C'`
``--copyright'`
  Prints a short note about the Copyright and copying conditions, then exit without further processing.
``-G'`
``--traditional'`
  As already explained, this option disables all GNU extensions to `ptx` and switch to traditional mode.
``--help'`
  Prints a short help on standard output, then exit without further processing.
``--version'`
  Prints the program verison on standard output, then exit without further processing.

### 7.5.2 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, unless if it is compiled for MS-DOS, in which case it uses the character set of the IBM-PC. (GNU `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.

``-f'`
``--ignore-case'`
  Fold lower case letters to upper case for sorting.

### 7.5.3 Word selection and input processing

``-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 cannot 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. There is a default Ignore file used by `ptx` when this option is not specified, usually found in ``/usr/local/lib/eign'` if this has not been changed at installation time. If you want to deactivate the default Ignore file, specify `/dev/null` instead.
``-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. 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.
``-r'`
``--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. For more information about reference production, see See section 7.5.4 Output formatting. 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, 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 ``-r'` option is not used, end of sentences are used. In this case, the precise 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 ""'`. See section `Syntax of Regular Expressions' in 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 `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, letting the default dive in. See section `Syntax of Regular Expressions' in 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 `ptx` itself.

### 7.5.4 Output formatting

Output format is mainly controlled by ``-O'` and ``-T'` options, described in the table below. When neither ``-O'` nor ``-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 ``-A'` and are output before the left context, that is, if option ``-R'` is not selected, then a colon is added after the reference; this nicely interfaces with GNU Emacs `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.

``-g number'`
``--gap-size=number'`
  Select the size of the minimum white gap between the fields on the output line.
``-w number'`
``--width=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 ``-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.
``-A'`
``--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 ``-A'` and ``-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.
``-R'`
``--right-side-refs'`
  In default output format, when option ``-R'` is not used, any reference produced by the effect of options ``-r'` or ``-A'` are given to the far right of output lines, after the right context. In default output format, when option ``-R'` is specified, references are rather given to the beginning of each output line, before the left context. For any other output format, option ``-R'` is almost ignored, except for the fact that the width of references is not taken into account in total output width given by ``-w'` whenever ``-R'` is selected. This option is automatically selected whenever GNU extensions are disabled.
``-F string'`
``--flac-truncation=string'`
  This option will request that any truncation in the output be reported using the string string. Most output fields theoretically extend towards the beginning or the end of the current line, or current sentence, as selected with option ``-S'`. But there is a maximum allowed output line width, changeable through option ``-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 ``-F /'`. string may have more than one character, as in ``-F ...'`. Also, in the particular case string is empty (``-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 `ptx` itself.
``-M string'`
``--macro-name=string'`
  Select another string to be used instead of ``xx'`, while generating output suitable for `nroff`, `troff` or TeX.
``-O'`
``--format=roff'`
  Choose an output format suitable for `nroff` or `troff` processing. Each output line will look like:

      .xx "tail" "before" "keyword_and_after" "head" "ref"

  so it will be possible to write an ``.xx'` roff macro to take care of the output typesetting. This is the default output format when GNU extensions are disabled. Option ``-M'` might be used to change ``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: `"` is doubled so it will be correctly processed by `nroff` or `troff`.
``-T'`
``--format=tex'`
  Choose an output format suitable for TeX processing. Each output line will look like:

      \xx {tail}{before}{keyword}{after}{head}{ref}

  so it will be possible to write a `\xx` definition to take care of the output typesetting. Note that when references are not being produced, that is, neither option ``-A'` nor option ``-r'` is selected, the last parameter of each `\xx` call is inhibited. Option ``-M'` might be used to change ``xx'` to another macro name. In this output format, some special characters, like `$`, `%`, `&`, `#` and `_` are automatically protected with a backslash. Curly brackets `{`, `}` 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 `\backslash{}`. Circumflex and tilde diacritics produce the sequence `^\{ }` and `~\{ }` 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.

### 7.5.5 The GNU extensions to `ptx`

This version of `ptx` contains a few features which do not exist in System V `ptx`. These extra features are suppressed by using the ``-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 ``-G'` if you care about GNU extensions. Here are the differences between this program and System V `ptx`.

- This program can read many input files at once, it always writes the resulting concordance on standard output. On the other end, System V `ptx` reads only one file and produce the result on standard output or, if a second file parameter is given on the command, to that file. Having output parameters not introduced by options is a quite dangerous practice which GNU avoids as far as possible. So, for using `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 ``-G'` option to `ptx` calls in products using `ptx`, if the configurator finds that the installed `ptx` accepts ``-G'`.
- The only options available in System V `ptx` are options ``-b'`, ``-f'`, ``-g'`, ``-i'`, ``-o'`, ``-r'`, ``-t'` and ``-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.
- By default, concordance output is not formatted for `troff` or `nroff`. It is rather formatted for a dumb terminal. `troff` or `nroff` output may still be selected through option ``-O'`.
- Unless ``-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.
- All 256 characters, even `NUL`s, are always read and processed from input file with no adverse effect, even if GNU extensions are disabled. However, System V `ptx` does not accept 8-bit characters, a few control characters are rejected, and the tilde `~` is condemned.
- Input line length is only limited by available memory, even if GNU extensions are disabled. However, System V `ptx` processes only the first 200 characters in each line.
- 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.
- The program makes better use of output line width. If GNU extensions are disabled, the program rather tries to imitate System V `ptx`, but still, there are some slight disposition glitches this program does not completely reproduce.
- The user can specify both an Ignore file and an Only file. This is not allowed with System V `ptx`.

Go to the first, previous, next, last section, table of contents.