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GNU Info File | 1997-01-26 | 125KB | 2,437 lines

This is Info file textutils.info, produced by Makeinfo version 1.67
from the input file textutils.texi.
START-INFO-DIR-ENTRY
* Text utilities: (textutils).          GNU text utilities.
* cat: (textutils)cat invocation.               Concatenate and write files.
* cksum: (textutils)cksum invocation.           Print POSIX CRC checksum.
* comm: (textutils)comm invocation.             Compare sorted files by line.
* csplit: (textutils)csplit invocation.         Split by context.
* cut: (textutils)cut invocation.               Print selected parts of lines.
* expand: (textutils)expand invocation.         Convert tabs to spaces.
* fmt: (textutils)fmt invocation.               Reformat paragraph text.
* fold: (textutils)fold invocation.             Wrap long input lines.
* head: (textutils)head invocation.             Output the first part of files.
* join: (textutils)join invocation.             Join lines on a common field.
* md5sum: (textutils)md5sum invocation.         Print or check message-digests.
* nl: (textutils)nl invocation.                 Number lines and write files.
* 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.
* sort: (textutils)sort invocation.             Sort text files.
* split: (textutils)split invocation.           Split into fixed-size pieces.
* sum: (textutils)sum invocation.               Print traditional checksum.
* tac: (textutils)tac invocation.               Reverse files.
* tail: (textutils)tail invocation.             Output the last part of files.
* tr: (textutils)tr invocation.                 Translate characters.
* unexpand: (textutils)unexpand invocation.     Convert spaces to tabs.
* uniq: (textutils)uniq invocation.             Uniqify files.
* wc: (textutils)wc invocation.                 Byte, word, and line counts.
END-INFO-DIR-ENTRY
   This file documents the GNU text utilities.
   Copyright (C) 1994, 95, 96 Free Software Foundation, Inc.
   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.
File: textutils.info,  Node: Top,  Next: Introduction,  Up: (dir)
GNU text utilities
******************
   This manual minimally documents version 1.22 of the GNU text
utilities.
* Menu:
* Introduction::                       Caveats, overview, and authors.
* Common options::                     Common options.
* Output of entire files::             cat tac nl od
* 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 fields within a line::  cut paste join
* Operating on characters::            tr expand unexpand
* Opening the software toolbox::       The software tools philosophy.
* Index::                              General index.
File: textutils.info,  Node: Introduction,  Next: Common options,  Prev: Top,  Up: Top
Introduction
************
   This manual is incomplete: No attempt is made to explain basic
concepts in a way suitable for novices.  Thus, if you are interested,
please get involved in improving this manual.  The entire GNU community
will benefit.
   The GNU text utilities are mostly compatible with the POSIX.2
standard.
   Please report bugs to `[e-mail]'.  Remember to
include the version number, machine architecture, input files, and any
other information needed to reproduce the bug: your input, what you
expected, what you got, and why it is wrong.  Diffs are welcome, but
please include a description of the problem as well, since this is
sometimes difficult to infer. *Note Bugs: (gcc)Bugs.
   This manual is based on the Unix man pages in the distribution, which
were originally written by David MacKenzie and updated by Jim Meyering.
The original `fmt' man page was written by Ross Paterson.  Franc,ois
Pinard did the initial conversion to Texinfo format.  Karl Berry did
the indexing, some reorganization, and editing of the results.  Richard
Stallman contributed his usual invaluable insights to the overall
process.
File: textutils.info,  Node: Common options,  Next: Output of entire files,  Prev: Introduction,  Up: Top
Common options
**************
   Certain options are available in all these programs.  Rather than
writing identical descriptions for each of the programs, they are
described here.  (In fact, every GNU program accepts (or should accept)
these options.)
   A few of these programs take arbitrary strings as arguments.  In
those cases, `--help' and `--version' are taken as these options only
if there is one and exactly one command line argument.
`--help'
     Print a usage message listing all available options, then exit
     successfully.
`--version'
     Print the version number, then exit successfully.
File: textutils.info,  Node: Output of entire files,  Next: Formatting file contents,  Prev: Common options,  Up: Top
Output of entire files
**********************
   These commands read and write entire files, possibly transforming
them in some way.
* Menu:
* 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.
File: textutils.info,  Node: cat invocation,  Next: tac invocation,  Up: Output of entire files
`cat': Concatenate and write files
==================================
   `cat' copies each FILE (`-' means standard input), or standard input
if none are given, to standard output.  Synopsis:
     cat [OPTION] [FILE]...
   The program accepts the following options.  Also see *Note Common
options::.
`--show-all'
     Equivalent to `-vET'.
`--number-nonblank'
     Number all nonblank output lines, starting with 1.
     Equivalent to `-vE'.
`--show-ends'
     Display a `$' after the end of each line.
`--number'
     Number all output lines, starting with 1.
`--squeeze-blank'
     Replace multiple adjacent blank lines with a single blank line.
     Equivalent to `-vT'.
`--show-tabs'
     Display <TAB> characters as `^I'.
     Ignored; for Unix compatibility.
`--show-nonprinting'
     Display control characters except for <LFD> and <TAB> using `^'
     notation and precede characters that have the high bit set with
     `M-'.
File: textutils.info,  Node: tac invocation,  Next: nl invocation,  Prev: cat invocation,  Up: Output of entire files
`tac': Concatenate and write files in reverse
=============================================
   `tac' copies each FILE (`-' means standard input), or standard input
if none are given, to standard output, reversing the records (lines by
default) in each separately.  Synopsis:
     tac [OPTION]... [FILE]...
   "Records" are separated by instances of a string (newline by
default).  By default, this separator string is attached to the end of
the record that it follows in the file.
   The program accepts the following options.  Also see *Note Common
options::.
`--before'
     The separator is attached to the beginning of the record that it
     precedes in the file.
`--regex'
     Treat the separator string as a regular expression.
`-s SEPARATOR'
`--separator=SEPARATOR'
     Use SEPARATOR as the record separator, instead of newline.
File: textutils.info,  Node: nl invocation,  Next: od invocation,  Prev: tac invocation,  Up: Output of entire files
`nl': Number lines and write files
==================================
   `nl' writes each FILE (`-' means standard input), or standard input
if none are given, to standard output, with line numbers added to some
or all of the lines.  Synopsis:
     nl [OPTION]... [FILE]...
   `nl' decomposes its input into (logical) pages; by default, the line
number is reset to 1 at the top of each logical page.  `nl' treats all
of the input files as a single document; it does not reset line numbers
or logical pages between files.
   A logical page consists of three sections: header, body, and footer.
Any of the sections can be empty.  Each can be numbered in a different
style from the others.
   The beginnings of the sections of logical pages are indicated in the
input file by a line containing exactly one of these delimiter strings:
`\:\:\:'
     start of header;
`\:\:'
     start of body;
     start of footer.
   The two characters from which these strings are made can be changed
from `\' and `:' via options (see below), but the pattern and length of
each string cannot be changed.
   A section delimiter is replaced by an empty line on output.  Any text
that comes before the first section delimiter string in the input file
is considered to be part of a body section, so `nl' treats a file that
contains no section delimiters as a single body section.
   The program accepts the following options.  Also see *Note Common
options::.
`-b STYLE'
`--body-numbering=STYLE'
     Select the numbering style for lines in the body section of each
     logical page.  When a line is not numbered, the current line number
     is not incremented, but the line number separator character is
     still prepended to the line.  The styles are:
    `a'
          number all lines,
    `t'
          number only nonempty lines (default for body),
    `n'
          do not number lines (default for header and footer),
    `pREGEXP'
          number only lines that contain a match for REGEXP.
`-d CD'
`--section-delimiter=CD'
     Set the section delimiter characters to CD; default is `\:'. If
     only C is given, the second remains `:'.  (Remember to protect `\'
     or other metacharacters from shell expansion with quotes or extra
     backslashes.)
`-f STYLE'
`--footer-numbering=STYLE'
     Analogous to `--body-numbering'.
`-h STYLE'
`--header-numbering=STYLE'
     Analogous to `--body-numbering'.
`-i NUMBER'
`--page-increment=NUMBER'
     Increment line numbers by NUMBER (default 1).
`-l NUMBER'
`--join-blank-lines=NUMBER'
     Consider NUMBER (default 1) consecutive empty lines to be one
     logical line for numbering, and only number the last one.  Where
     fewer than NUMBER consecutive empty lines occur, do not number
     them.  An empty line is one that contains no characters, not even
     spaces or tabs.
`-n FORMAT'
`--number-format=FORMAT'
     Select the line numbering format (default is `rn'):
    `ln'
          left justified, no leading zeros;
    `rn'
          right justified, no leading zeros;
    `rz'
          right justified, leading zeros.
`--no-renumber'
     Do not reset the line number at the start of a logical page.
`-s STRING'
`--number-separator=STRING'
     Separate the line number from the text line in the output with
     STRING (default is <TAB>).
`-v NUMBER'
`--starting-line-number=NUMBER'
     Set the initial line number on each logical page to NUMBER
     (default 1).
`-w NUMBER'
`--number-width=NUMBER'
     Use NUMBER characters for line numbers (default 6).
File: textutils.info,  Node: od invocation,  Prev: nl invocation,  Up: Output of entire files
`od': Write files in octal or other formats
===========================================
   `od' writes an unambiguous representation of each FILE (`-' means
standard input), or standard input if none are given.  Synopsis:
     od [OPTION]... [FILE]...
     od -C [FILE] [[+]OFFSET [[+]LABEL]]
   Each line of output consists of the offset in the input, followed by
groups of data from the file. By default, `od' prints the offset in
octal, and each group of file data is two bytes of input printed as a
single octal number.
   The program accepts the following options.  Also see *Note Common
options::.
`-A RADIX'
`--address-radix=RADIX'
     Select the base in which file offsets are printed.  RADIX can be
     one of the following:
    `d'
          decimal;
    `o'
          octal;
    `x'
          hexadecimal;
    `n'
          none (do not print offsets).
     The default is octal.
`-j BYTES'
`--skip-bytes=BYTES'
     Skip BYTES input bytes before formatting and writing.  If BYTES
     begins with `0x' or `0X', it is interpreted in hexadecimal;
     otherwise, if it begins with `0', in octal; otherwise, in decimal.
     Appending `b' multiplies BYTES by 512, `k' by 1024, and `m' by
     1048576.
`-N BYTES'
`--read-bytes=BYTES'
     Output at most BYTES bytes of the input.  Prefixes and suffixes on
     `bytes' are interpreted as for the `-j' option.
`-s [N]'
`--strings[=N]'
     Instead of the normal output, output only "string constants": at
     least N (3 by default) consecutive ASCII graphic characters,
     followed by a null (zero) byte.
`-t TYPE'
`--format=TYPE'
     Select the format in which to output the file data.  TYPE is a
     string of one or more of the below type indicator characters.  If
     you include more than one type indicator character in a single TYPE
     string, or use this option more than once, `od' writes one copy of
     each output line using each of the data types that you specified,
     in the order that you specified.
    `a'
          named character,
    `c'
          ASCII character or backslash escape,
    `d'
          signed decimal,
    `f'
          floating point,
    `o'
          octal,
    `u'
          unsigned decimal,
    `x'
          hexadecimal.
     The type `a' outputs things like `sp' for space, `nl' for newline,
     and `nul' for a null (zero) byte.  Type `c' outputs ` ', `\n', and
     `\0', respectively.
     Except for types `a' and `c', you can specify the number of bytes
     to use in interpreting each number in the given data type by
     following the type indicator character with a decimal integer.
     Alternately, you can specify the size of one of the C compiler's
     built-in data types by following the type indicator character with
     one of the following characters.  For integers (`d', `o', `u',
     `x'):
    `C'
          char,
    `S'
          short,
    `I'
          int,
    `L'
          long.
     For floating point (`f'):
    F
          float,
    D
          double,
    L
          long double.
`--output-duplicates'
     Output consecutive lines that are identical.  By default, when two
     or more consecutive output lines would be identical, `od' outputs
     only the first line, and puts just an asterisk on the following
     line to indicate the elision.
`-w[N]'
`--width[=N]'
     Dump `n' input bytes per output line.  This must be a multiple of
     the least common multiple of the sizes associated with the
     specified output types.  If N is omitted, the default is 32.  If
     this option is not given at all, the default is 16.
   The next several options map the old, pre-POSIX format specification
options to the corresponding POSIX format specs.  GNU `od' accepts any
combination of old- and new-style options.  Format specification
options accumulate.
     Output as named characters.  Equivalent to `-ta'.
     Output as octal bytes.  Equivalent to `-toC'.
     Output as ASCII characters or backslash escapes.  Equivalent to
     `-tc'.
     Output as unsigned decimal shorts.  Equivalent to `-tu2'.
     Output as floats.  Equivalent to `-tfF'.
     Output as hexadecimal shorts.  Equivalent to `-tx2'.
     Output as decimal shorts.  Equivalent to `-td2'.
     Output as decimal longs.  Equivalent to `-td4'.
     Output as octal shorts.  Equivalent to `-to2'.
     Output as hexadecimal shorts.  Equivalent to `-tx2'.
`--traditional'
     Recognize the pre-POSIX non-option arguments that traditional `od'
     accepted.  The following syntax:
          od --traditional [FILE] [[+]OFFSET[.][b] [[+]LABEL[.][b]]]
     can be used to specify at most one file and optional arguments
     specifying an offset and a pseudo-start address, LABEL.  By
     default, OFFSET is interpreted as an octal number specifying how
     many input bytes to skip before formatting and writing.  The
     optional trailing decimal point forces the interpretation of
     OFFSET as a decimal number.  If no decimal is specified and the
     offset begins with `0x' or `0X' it is interpreted as a hexadecimal
     number.  If there is a trailing `b', the number of bytes skipped
     will be OFFSET multiplied by 512.  The LABEL argument is
     interpreted just like OFFSET, but it specifies an initial
     pseudo-address.  The pseudo-addresses are displayed in parentheses
     following any normal address.
File: textutils.info,  Node: Formatting file contents,  Next: Output of parts of files,  Prev: Output of entire files,  Up: Top
Formatting file contents
************************
   These commands reformat the contents of files.
* Menu:
* fmt invocation::              Reformat paragraph text.
* pr invocation::               Paginate or columnate files for printing.
* fold invocation::             Wrap input lines to fit in specified width.
File: textutils.info,  Node: fmt invocation,  Next: pr invocation,  Up: Formatting file contents
`fmt': Reformat paragraph text
==============================
   `fmt' fills and joins lines to produce output lines of (at most) a
given number of characters (75 by default).  Synopsis:
     fmt [OPTION]... [FILE]...
   `fmt' reads from the specified FILE arguments (or standard input if
none are given), and writes to standard output.
   By default, blank lines, spaces between words, and indentation are
preserved in the output; successive input lines with different
indentation are not joined; tabs are expanded on input and introduced on
output.
   `fmt' prefers breaking lines at the end of a sentence, and tries to
avoid line breaks after the first word of a sentence or before the last
word of a sentence.  A "sentence break" is defined as either the end of
a paragraph or a word ending in any of `.?!', followed by two spaces or
end of line, ignoring any intervening parentheses or quotes.  Like TeX,
`fmt' reads entire "paragraphs" before choosing line breaks; the
algorithm is a variant of that in "Breaking Paragraphs Into Lines"
(Donald E. Knuth and Michael F. Plass, `Software--Practice and
Experience', 11 (1981), 1119-1184).
   The program accepts the following options.  Also see *Note Common
options::.
`--crown-margin'
     "Crown margin" mode: preserve the indentation of the first two
     lines within a paragraph, and align the left margin of each
     subsequent line with that of the second line.
`--tagged-paragraph'
     "Tagged paragraph" mode: like crown margin mode, except that if
     indentation of the first line of a paragraph is the same as the
     indentation of the second, the first line is treated as a one-line
     paragraph.
`--split-only'
     Split lines only.  Do not join short lines to form longer ones.
     This prevents sample lines of code, and other such "formatted"
     text from being unduly combined.
`--uniform-spacing'
     Uniform spacing.  Reduce spacing between words to one space, and
     spacing between sentences to two spaces.
`-WIDTH'
`-w WIDTH'
`--width=WIDTH'
     Fill output lines up to WIDTH characters (default 75).  `fmt'
     initially tries to make lines about 7% shorter than this, to give
     it room to balance line lengths.
`-p PREFIX'
`--prefix=PREFIX'
     Only lines beginning with PREFIX (possibly preceded by whitespace)
     are subject to formatting. The prefix and any preceding whitespace
     are stripped for the formatting and then re-attached to each
     formatted output line.  One use is to format certain kinds of
     program comments, while leaving the code unchanged.
File: textutils.info,  Node: pr invocation,  Next: fold invocation,  Prev: fmt invocation,  Up: Formatting file contents
`pr': Paginate or columnate files for printing
==============================================
   `pr' writes each FILE (`-' means standard input), or standard input
if none are given, to standard output, paginating and optionally
outputting in multicolumn format; optionally merges all FILEs, printing
all in parallel, one per column.  Synopsis:
     pr [OPTION]... [FILE]...
   By default, a 5-line header is printed: two blank lines; a line with
the date, the file name, and the page count; and two more blank lines.
A footer of five blank lines is also printed. With the `-f' option, a
3-line header is printed: the leading two blank lines are omitted; no
footer used. The default PAGE_LENGTH in both cases is 66 lines.  The
text line of the header takes up the full PAGE_WIDTH in the form
`yy-mm-dd HH:MM string Page nnnn'. String is a centered string.
   Form feeds in the input cause page breaks in the output. Multiple
form feeds produce empty pages.
   Columns have equal width, separated by an optional string (default
space). Lines will always be truncated to line width (default 72),
unless you use the `-j' option. For single column output no line
truncation occurs by default. Use `-w' option to truncate lines in that
case.
   The program accepts the following options.  Also see *Note Common
options::.
`+FIRST_PAGE[:LAST_PAGE]'
     Begin printing with page FIRST_PAGE and stop with LAST_PAGE.
     Missing `: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 `+FIRST_PAGE' is
     identical. By default, it starts with the first page of input file
     (not first page printed). Page numbering may be altered by `-N'
     option.
`-COLUMN'
     With each single FILE, produce COLUMN-column output and print
     columns down. The column width is automatically estimated from
     PAGE_WIDTH. This option might well cause some columns to be
     truncated. The number of lines in the columns on each page will be
     balanced. `-COLUMN' may not be used with `-m' option.
     With each single FILE, print columns across rather than down.
     COLUMN must be greater than one.
     Print control characters using hat notation (e.g., `^G'); print
     other unprintable characters in octal backslash notation.  By
     default, unprintable characters are not changed.
     Double space the output.
`-e[IN-TABCHAR[IN-TABWIDTH]]'
     Expand tabs to spaces on input.  Optional argument IN-TABCHAR is
     the input tab character (default is <TAB>).  Second optional
     argument IN-TABWIDTH is the input tab character's width (default
     is 8).
     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.
`-h HEADER'
     Replace the file name in the header with the centered string
     HEADER. Left-hand-side truncation (marked by a `*') may occur if
     the total header line `yy-mm-dd HH:MM HEADER Page nnnn' becomes
     larger than PAGE_WIDTH. `-h ""' prints a blank line header. Don't
     use `-h""'. A space between the -h option and the argument is
     always peremptory.
`-i[OUT-TABCHAR[OUT-TABWIDTH]]'
     Replace spaces with tabs on output.  Optional argument OUT-TABCHAR
     is the output tab character (default is <TAB>).  Second optional
     argument OUT-TABWIDTH is the output tab character's width (default
     is 8).
     Merge lines of full length. Used together with the column options
     `-COLUMN', `-a -COLUMN' or `-m'. Turns off `-w' line truncation;
     no column alignment used; may be used with `-s[SEPARATOR]'.
`-l PAGE_LENGTH'
     Set the page length to PAGE_LENGTH (default 66) lines. If
     PAGE_LENGTH is less than or equal 10 (and <= 3 with `-f'), the
     headers and footers are omitted, and all form feeds set in input
     files are eliminated, as if the `-T' option had been given.
     Merge and print all FILEs in parallel, one in each column. If a
     line is too long to fit in a column, it is truncated (but see
     `-j'). `-s[SEPARATOR]' may be used. Empty pages in some FILEs
     (form feeds set) produce empty columns, still marked by SEPARATOR.
     Completely empty common pages show no separators or line numbers.
     The default header becomes `yy-mm-dd HH:MM <blanks> Page nnnn';
     may be used with `-h HEADER' to fill up the middle part.
`-n[NUMBER-SEPARATOR[DIGITS]]'
     Precede each column with a line number; with parallel FILEs
     (`-m'), precede only each line with a line number. Optional
     argument NUMBER-SEPARATOR is the character to print after each
     number (default is <TAB>).  Optional argument DIGITS is the number
     of digits per line number (default is 5). Default line counting
     starts with first line of the input file (not with the first line
     printed, see `-N').
`-N LINE_NUMBER'
     Start line counting with no. LINE_NUMBER at first line of first
     page printed.
`-o N'
     Indent each line with N (default is zero) spaces wide, i.e., set
     the left margin.  The total page width is N plus the width set
     with the `-w' option.
     Do not print a warning message when an argument FILE cannot be
     opened.  (The exit status will still be nonzero, however.)
`-s[SEPARATOR]'
     Separate columns by a string SEPARATOR. Don't use `-s SEPARATOR',
     no space between flag and argument. If this option is omitted
     altogether, the default is a space, same as `-s" "'. With `-s'
     only, no separator is used, same as `-s""'. `-s' does not affect
     line truncation or column alignment.
     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 predefined page layout is not changed. `-t'
     or `-T' may be useful together with other options; e.g.: `-t -e4',
     expand <TAB> in the input file to 4 spaces but do not do any other
     changes.  Use of `-t' overrides `-h'.
     Do not print header [and footer]. In addition eliminate all form
     feeds set in the input files.
     Print unprintable characters in octal backslash notation.
`-w PAGE_WIDTH'
     Set the page width to PAGE_WIDTH (default 72) characters.
     With/without `-w', header lines are always truncated to PAGE_WIDTH
     characters. With `-w', text lines are truncated, unless `-j' is
     used. Without `-w' together with one of the column options
     `-COLUMN', `-a -COLUMN' or `-m', default truncation of text lines
     to 72 characters is used.  Without `-w' and without any of the
     column options, no line truncation is used. That's equivalent to
     `-w 72 -j'.
File: textutils.info,  Node: fold invocation,  Prev: pr invocation,  Up: Formatting file contents
`fold': Wrap input lines to fit in specified width
==================================================
   `fold' writes each FILE (`-' means standard input), or standard
input if none are given, to standard output, breaking long lines.
Synopsis:
     fold [OPTION]... [FILE]...
   By default, `fold' breaks lines wider than 80 columns. The output is
split into as many lines as necessary.
   `fold' counts screen columns by default; thus, a tab may count more
than one column, backspace decreases the column count, and carriage
return sets the column to zero.
   The program accepts the following options.  Also see *Note Common
options::.
`--bytes'
     Count bytes rather than columns, so that tabs, backspaces, and
     carriage returns are each counted as taking up one column, just
     like other characters.
`--spaces'
     Break at word boundaries: the line is broken after the last blank
     before the maximum line length.  If the line contains no such
     blanks, the line is broken at the maximum line length as usual.
`-w WIDTH'
`--width=WIDTH'
     Use a maximum line length of WIDTH columns instead of 80.
File: textutils.info,  Node: Output of parts of files,  Next: Summarizing files,  Prev: Formatting file contents,  Up: Top
Output of parts of files
************************
   These commands output pieces of the input.
* Menu:
* 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.
File: textutils.info,  Node: head invocation,  Next: tail invocation,  Up: Output of parts of files
`head': Output the first part of files
======================================
   `head' prints the first part (10 lines by default) of each FILE; it
reads from standard input if no files are given or when given a FILE of
`-'.  Synopses:
     head [OPTION]... [FILE]...
     head -NUMBER [OPTION]... [FILE]...
   If more than one FILE is specified, `head' prints a one-line header
consisting of
     ==> FILE NAME <==
before the output for each FILE.
   `head' accepts two option formats: the new one, in which numbers are
arguments to the options (`-q -n 1'), and the old one, in which the
number precedes any option letters (`-1q').
   The program accepts the following options.  Also see *Note Common
options::.
`-COUNTOPTIONS'
     This option is only recognized if it is specified first.  COUNT is
     a decimal number optionally followed by a size letter (`b', `k',
     `m') as in `-c', or `l' to mean count by lines, or other option
     letters (`cqv').
`-c BYTES'
`--bytes=BYTES'
     Print the first BYTES bytes, instead of initial lines.  Appending
     `b' multiplies BYTES by 512, `k' by 1024, and `m' by 1048576.
`-n N'
`--lines=N'
     Output the first N lines.
`--quiet'
`--silent'
     Never print file name headers.
`--verbose'
     Always print file name headers.
File: textutils.info,  Node: tail invocation,  Next: split invocation,  Prev: head invocation,  Up: Output of parts of files
`tail': Output the last part of files
=====================================
   `tail' prints the last part (10 lines by default) of each FILE; it
reads from standard input if no files are given or when given a FILE of
`-'.  Synopses:
     tail [OPTION]... [FILE]...
     tail -NUMBER [OPTION]... [FILE]...
     tail +NUMBER [OPTION]... [FILE]...
   If more than one FILE is specified, `tail' prints a one-line header
consisting of
     ==> FILE NAME <==
before the output for each FILE.
   GNU `tail' can output any amount of data (some other versions of
`tail' cannot).  It also has no `-r' option (print in reverse), since
reversing a file is really a different job from printing the end of a
file; BSD `tail' (which is the one with `-r') can only reverse files
that are at most as large as its buffer, which is typically 32k.  A
more reliable and versatile way to reverse files is the GNU `tac'
command.
   `tail' accepts two option formats: the new one, in which numbers are
arguments to the options (`-n 1'), and the old one, in which the number
precedes any option letters (`-1' or `+1').
   If any option-argument is a number N starting with a `+', `tail'
begins printing with the Nth item from the start of each file, instead
of from the end.
   The program accepts the following options.  Also see *Note Common
options::.
`-COUNT'
`+COUNT'
     This option is only recognized if it is specified first.  COUNT is
     a decimal number optionally followed by a size letter (`b', `k',
     `m') as in `-c', or `l' to mean count by lines, or other option
     letters (`cfqv').
`-c BYTES'
`--bytes=BYTES'
     Output the last BYTES bytes, instead of final lines.  Appending
     `b' multiplies BYTES by 512, `k' by 1024, and `m' by 1048576.
`--follow'
     Loop forever trying to read more characters at the end of the file,
     presumably because the file is growing.  Ignored if reading from a
     pipe.  If more than one file is given, `tail' prints a header
     whenever it gets output from a different file, to indicate which
     file that output is from.
`-n N'
`--lines=N'
     Output the last N lines.
`-quiet'
`--silent'
     Never print file name headers.
`--verbose'
     Always print file name headers.
File: textutils.info,  Node: split invocation,  Next: csplit invocation,  Prev: tail invocation,  Up: Output of parts of files
`split': Split a file into fixed-size pieces
============================================
   `split' creates output files containing consecutive sections of
INPUT (standard input if none is given or INPUT is `-').  Synopsis:
     split [OPTION] [INPUT [PREFIX]]
   By default, `split' puts 1000 lines of INPUT (or whatever is left
over for the last section), into each output file.
   The output files' names consist of PREFIX (`x' by default) followed
by a group of letters `aa', `ab', and so on, such that concatenating
the output files in sorted order by file name produces the original
input file.  (If more than 676 output files are required, `split' uses
`zaa', `zab', etc.)
   The program accepts the following options.  Also see *Note Common
options::.
`-LINES'
`-l LINES'
`--lines=LINES'
     Put LINES lines of INPUT into each output file.
`-b BYTES'
`--bytes=BYTES'
     Put the first BYTES bytes of INPUT into each output file.
     Appending `b' multiplies BYTES by 512, `k' by 1024, and `m' by
     1048576.
`-C BYTES'
`--line-bytes=BYTES'
     Put into each output file as many complete lines of INPUT as
     possible without exceeding BYTES bytes.  For lines longer than
     BYTES bytes, put BYTES bytes into each output file until less than
     BYTES bytes of the line are left, then continue normally.  BYTES
     has the same format as for the `--bytes' option.
`--verbose'
     Write a diagnostic to standard error just before each output file
     is opened.
File: textutils.info,  Node: csplit invocation,  Prev: split invocation,  Up: Output of parts of files
`csplit': Split a file into context-determined pieces
=====================================================
   `csplit' creates zero or more output files containing sections of
INPUT (standard input if INPUT is `-').  Synopsis:
     csplit [OPTION]... INPUT PATTERN...
   The contents of the output files are determined by the PATTERN
arguments, as detailed below.  An error occurs if a PATTERN argument
refers to a nonexistent line of the input file (e.g., if no remaining
line matches a given regular expression).  After every PATTERN has been
matched, any remaining input is copied into one last output file.
   By default, `csplit' prints the number of bytes written to each
output file after it has been created.
   The types of pattern arguments are:
     Create an output file containing the input up to but not including
     line N (a positive integer).  If followed by a repeat count, also
     create an output file containing the next LINE lines of the input
     file once for each repeat.
`/REGEXP/[OFFSET]'
     Create an output file containing the current line up to (but not
     including) the next line of the input file that contains a match
     for REGEXP.  The optional OFFSET is a `+' or `-' followed by a
     positive integer.  If it is given, the input up to the matching
     line plus or minus OFFSET is put into the output file, and the
     line after that begins the next section of input.
`%REGEXP%[OFFSET]'
     Like the previous type, except that it does not create an output
     file, so that section of the input file is effectively ignored.
`{REPEAT-COUNT}'
     Repeat the previous pattern REPEAT-COUNT additional times.
     REPEAT-COUNT can either be a positive integer or an asterisk,
     meaning repeat as many times as necessary until the input is
     exhausted.
   The output files' names consist of a prefix (`xx' by default)
followed by a suffix.  By default, the suffix is an ascending sequence
of two-digit decimal numbers from `00' and up to `99'.  In any case,
concatenating the output files in sorted order by filename produces the
original input file.
   By default, if `csplit' encounters an error or receives a hangup,
interrupt, quit, or terminate signal, it removes any output files that
it has created so far before it exits.
   The program accepts the following options.  Also see *Note Common
options::.
`-f PREFIX'
`--prefix=PREFIX'
     Use PREFIX as the output file name prefix.
`-b SUFFIX'
`--suffix=SUFFIX'
     Use SUFFIX as the output file name suffix.  When this option is
     specified, the suffix string must include exactly one
     `printf(3)'-style conversion specification, possibly including
     format specification flags, a field width, a precision
     specifications, or all of these kinds of modifiers.  The format
     letter must convert a binary integer argument to readable form;
     thus, only `d', `i', `u', `o', `x', and `X' conversions are
     allowed.  The entire SUFFIX is given (with the current output file
     number) to `sprintf(3)' to form the file name suffixes for each of
     the individual output files in turn.  If this option is used, the
     `--digits' option is ignored.
`-n DIGITS'
`--digits=DIGITS'
     Use output file names containing numbers that are DIGITS digits
     long instead of the default 2.
`--keep-files'
     Do not remove output files when errors are encountered.
`--elide-empty-files'
     Suppress the generation of zero-length output files.  (In cases
     where the section delimiters of the input file are supposed to
     mark the first lines of each of the sections, the first output
     file will generally be a zero-length file unless you use this
     option.)  The output file sequence numbers always run
     consecutively starting from 0, even when this option is specified.
`--silent'
`--quiet'
     Do not print counts of output file sizes.
File: textutils.info,  Node: Summarizing files,  Next: Operating on sorted files,  Prev: Output of parts of files,  Up: Top
Summarizing files
*****************
   These commands generate just a few numbers representing entire
contents of files.
* Menu:
* 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.
File: textutils.info,  Node: wc invocation,  Next: sum invocation,  Up: Summarizing files
`wc': Print byte, word, and line counts
=======================================
   `wc' counts the number of bytes, whitespace-separated words, and
newlines in each given FILE, or standard input if none are given or for
a FILE of `-'.  Synopsis:
     wc [OPTION]... [FILE]...
   `wc' prints one line of counts for each file, and if the file was
given as an argument, it prints the file name following the counts.  If
more than one FILE is given, `wc' prints a final line containing the
cumulative counts, with the file name `total'.  The counts are printed
in this order: newlines, words, bytes.
   By default, `wc' prints all three counts.  Options can specify that
only certain counts be printed.  Options do not undo others previously
given, so
     wc --bytes --words
prints both the byte counts and the word counts.
   The program accepts the following options.  Also see *Note Common
options::.
`--bytes'
`--chars'
     Print only the byte counts.
`--words'
     Print only the word counts.
`--lines'
     Print only the newline counts.
File: textutils.info,  Node: sum invocation,  Next: cksum invocation,  Prev: wc invocation,  Up: Summarizing files
`sum': Print checksum and block counts
======================================
   `sum' computes a 16-bit checksum for each given FILE, or standard
input if none are given or for a FILE of `-'.  Synopsis:
     sum [OPTION]... [FILE]...
   `sum' prints the checksum for each FILE followed by the number of
blocks in the file (rounded up).  If more than one FILE is given, file
names are also printed (by default).  (With the `--sysv' option,
corresponding file name are printed when there is at least one file
argument.)
   By default, GNU `sum' computes checksums using an algorithm
compatible with BSD `sum' and prints file sizes in units of 1024-byte
blocks.
   The program accepts the following options.  Also see *Note Common
options::.
     Use the default (BSD compatible) algorithm.  This option is
     included for compatibility with the System V `sum'.  Unless `-s'
     was also given, it has no effect.
`--sysv'
     Compute checksums using an algorithm compatible with System V
     `sum''s default, and print file sizes in units of 512-byte blocks.
   `sum' is provided for compatibility; the `cksum' program (see next
section) is preferable in new applications.
File: textutils.info,  Node: cksum invocation,  Next: md5sum invocation,  Prev: sum invocation,  Up: Summarizing files
`cksum': Print CRC checksum and byte counts
===========================================
   `cksum' computes a cyclic redundancy check (CRC) checksum for each
given FILE, or standard input if none are given or for a FILE of `-'.
Synopsis:
     cksum [OPTION]... [FILE]...
   `cksum' prints the CRC checksum for each file along with the number
of bytes in the file, and the filename unless no arguments were given.
   `cksum' is typically used to ensure that files transferred by
unreliable means (e.g., netnews) have not been corrupted, by comparing
the `cksum' output for the received files with the `cksum' output for
the original files (typically given in the distribution).
   The CRC algorithm is specified by the POSIX.2 standard.  It is not
compatible with the BSD or System V `sum' algorithms (see the previous
section); it is more robust.
   The only options are `--help' and `--version'.  *Note Common
options::.
File: textutils.info,  Node: md5sum invocation,  Prev: cksum invocation,  Up: Summarizing files
`md5sum': Print or check message-digests
========================================
   `md5sum' computes a 128-bit checksum (or "fingerprint" or
"message-digest") for each specified FILE.  If a FILE is specified as
`-' or if no files are given `md5sum' computes the checksum for the
standard input.  `md5sum' can also determine whether a file and
checksum are consistent. Synopsis:
     md5sum [OPTION]... [FILE]...
     md5sum [OPTION]... --check [FILE]
   For each FILE, `md5sum' outputs the MD5 checksum, a flag indicating
a binary or text input file, and the filename.  If FILE is omitted or
specified as `-', standard input is read.
   The program accepts the following options.  Also see *Note Common
options::.
`--binary'
     Treat all input files as binary.  This option has no effect on Unix
     systems, since they don't distinguish between binary and text
     files.  This option is useful on systems that have different
     internal and external character representations.
`--check'
     Read filenames and checksum information from the single FILE (or
     from stdin if no FILE was specified) and report whether each named
     file and the corresponding checksum data are consistent.  The
     input to this mode of `md5sum' is usually the output of a prior,
     checksum-generating run of `md5sum'.  Each valid line of input
     consists of an MD5 checksum, a binary/text flag, and then a
     filename.  Binary files are marked with `*', text with ` '.  For
     each such line, `md5sum' reads the named file and computes its MD5
     checksum.  Then, if the computed message digest does not match the
     one on the line with the filename, the file is noted as having
     failed the test.  Otherwise, the file passes the test.  By
     default, for each valid line, one line is written to standard
     output indicating whether the named file passed the test.  After
     all checks have been performed, if there were any failures, a
     warning is issued to standard error.  Use the `--status' option to
     inhibit that output.  If any listed file cannot be opened or read,
     if any valid line has an MD5 checksum inconsistent with the
     associated file, or if no valid line is found, `md5sum' exits with
     nonzero status.  Otherwise, it exits successfully.
`--status'
     This option is useful only when verifying checksums.  When
     verifying checksums, don't generate the default one-line-per-file
     diagnostic and don't output the warning summarizing any failures.
     Failures to open or read a file still evoke individual diagnostics
     to standard error.  If all listed files are readable and are
     consistent with the associated MD5 checksums, exit successfully.
     Otherwise exit with a status code indicating there was a failure.
`--text'
     Treat all input files as text files.  This is the reverse of
     `--binary'.
`--warn'
     When verifying checksums, warn about improperly formated MD5
     checksum lines.  This option is useful only if all but a few lines
     in the checked input are valid.
File: textutils.info,  Node: Operating on sorted files,  Next: Operating on fields within a line,  Prev: Summarizing files,  Up: Top
Operating on sorted files
*************************
   These commands work with (or produce) sorted files.
* Menu:
* sort invocation::             Sort text files.
* uniq invocation::             Uniqify files.
* comm invocation::             Compare two sorted files line by line.
File: textutils.info,  Node: sort invocation,  Next: uniq invocation,  Up: Operating on sorted files
`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:
     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.
     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.
   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 lines byte
by byte in machine collating sequence.  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.
   Upon any error, `sort' exits with a status of `2'.
   If the environment variable `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.
     Ignore leading blanks when finding sort keys in each line.
     Sort in "phone directory" order: ignore all characters except
     letters, digits and blanks when sorting.
     Fold lowercase characters into the equivalent uppercase characters
     when sorting so that, for example, `b' and `B' sort as equal.
     Sort numerically, but use strtod(3) to arrive at the numeric
     values.  This allows floating point numbers to be specified in
     scientific notation, like `1.0e-34' and `10e100'.  Use this option
     only if there is no alternative;  it is much slower than `-n' and
     numbers with too many significant digits will be compared as if
     they had been truncated.  In addition, numbers outside the range
     of representable double precision floating point numbers are
     treated as if they were zeroes; overflow and underflow are not
     reported.
     Ignore characters outside the printable ASCII range 040-0176 octal
     (inclusive) when sorting.
     An initial string, consisting of any amount of whitespace, followed
     by three letters abbreviating a month name, is folded to UPPER
     case and compared in the order `JAN' < `FEB' < ... < `DEC'.
     Invalid names compare low to valid names.
     Sort numerically: the number begins each line; specifically, it
     consists of optional whitespace, an optional `-' sign, and zero or
     more digits, optionally followed by a decimal point and zero or
     more digits.
     `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 decimal points 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.
     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.
     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 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.  See below.
     Treat the input as a set of lines, each terminated by a zero byte
     (ASCII NUL (Null) character) instead of a 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.  *Note 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
File: textutils.info,  Node: uniq invocation,  Next: comm invocation,  Prev: sort invocation,  Up: Operating on sorted files
`uniq': Uniqify 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 *Note Common
options::.
`-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.
`-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.
`--count'
     Print the number of times each line occurred along with the line.
`--ignore-case'
     Ignore differences in case when comparing lines.
`--repeated'
     Print only duplicate lines.
`--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.
File: textutils.info,  Node: comm invocation,  Prev: uniq invocation,  Up: Operating on sorted files
`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
   The input files must be sorted before `comm' can be used.
   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 <TAB>.
   The options `-1', `-2', and `-3' suppress printing of the
corresponding columns.  Also see *Note Common options::.
File: textutils.info,  Node: Operating on fields within a line,  Next: Operating on characters,  Prev: Operating on sorted files,  Up: Top
Operating on fields within a line
*********************************
* Menu:
* cut invocation::              Print selected parts of lines.
* paste invocation::            Merge lines of files.
* join invocation::             Join lines on a common field.
File: textutils.info,  Node: cut invocation,  Next: paste invocation,  Up: Operating on fields within a line
`cut': Print selected parts of lines
====================================
   `cut' writes to standard output selected parts of each line of each
input file, or standard input if no files are given or for a file name
of `-'.  Synopsis:
     cut [OPTION]... [FILE]...
   In the table which follows, the BYTE-LIST, CHARACTER-LIST, and
FIELD-LIST are one or more numbers or ranges (two numbers separated by
a dash) separated by commas.  Bytes, characters, and fields are
numbered from starting at 1.  Incomplete ranges may be given: `-M'
means `1-M'; `N-' means `N' through end of line or last field.
   The program accepts the following options.  Also see *Note Common
options::.
`-b BYTE-LIST'
`--bytes=BYTE-LIST'
     Print only the bytes in positions listed in BYTE-LIST.  Tabs and
     backspaces are treated like any other character; they take up 1
     byte.
`-c CHARACTER-LIST'
`--characters=CHARACTER-LIST'
     Print only characters in positions listed in CHARACTER-LIST.  The
     same as `-b' for now, but internationalization will change that.
     Tabs and backspaces are treated like any other character; they
     take up 1 character.
`-f FIELD-LIST'
`--fields=FIELD-LIST'
     Print only the fields listed in FIELD-LIST.  Fields are separated
     by a <TAB> by default.
`-d DELIM'
`--delimiter=DELIM'
     For `-f', fields are separated by the first character in DELIM
     (default is <TAB>).
     Do not split multi-byte characters (no-op for now).
`--only-delimited'
     For `-f', do not print lines that do not contain the field
     separator character.
File: textutils.info,  Node: paste invocation,  Next: join invocation,  Prev: cut invocation,  Up: Operating on fields within a line
`paste': Merge lines of files
=============================
   `paste' writes to standard output lines consisting of sequentially
corresponding lines of each given file, separated by <TAB>.  Standard
input is used for a file name of `-' or if no input files are given.
   Synopsis:
     paste [OPTION]... [FILE]...
   The program accepts the following options.  Also see *Note Common
options::.
`--serial'
     Paste the lines of one file at a time rather than one line from
     each file.
`-d DELIM-LIST'
`--delimiters DELIM-LIST'
     Consecutively use the characters in DELIM-LIST instead of <TAB> to
     separate merged lines.  When DELIM-LIST is exhausted, start again
     at its beginning.
File: textutils.info,  Node: join invocation,  Prev: paste invocation,  Up: Operating on fields within a line
`join': Join lines on a common field
====================================
   `join' writes to standard output a line for each pair of input lines
that have identical join fields.  Synopsis:
     join [OPTION]... FILE1 FILE2
   Either FILE1 or FILE2 (but not both) can be `-', meaning standard
input.  FILE1 and FILE2 should be already sorted in increasing order
(not numerically) on the join fields; unless the `-t' option is given,
they should be sorted ignoring blanks at the start of the join field,
as in `sort -b'.  If the `--ignore-case' option is given, lines should
be sorted without regard to the case of characters in the join field,
as in `sort -f'.
   The defaults are: the join field is the first field in each line;
fields in the input are separated by one or more blanks, with leading
blanks on the line ignored; fields in the output are separated by a
space; each output line consists of the join field, the remaining
fields from FILE1, then the remaining fields from FILE2.
   The program accepts the following options.  Also see *Note Common
options::.
`-a FILE-NUMBER'
     Print a line for each unpairable line in file FILE-NUMBER (either
     `1' or `2'), in addition to the normal output.
`-e STRING'
     Replace those output fields that are missing in the input with
     STRING.
`--ignore-case'
     Ignore differences in case when comparing keys.  With this option,
     the lines of the input files must be ordered in the same way.  Use
     `sort -f' to produce this ordering.
`-1 FIELD'
`-j1 FIELD'
     Join on field FIELD (a positive integer) of file 1.
`-2 FIELD'
`-j2 FIELD'
     Join on field FIELD (a positive integer) of file 2.
`-j FIELD'
     Equivalent to `-1 FIELD -2 FIELD'.
`-o FIELD-LIST...'
     Construct each output line according to the format in FIELD-LIST.
     Each element in FIELD-LIST is either the single character `0' or
     has the form M.N where the file number, M, is `1' or `2' and N is
     a positive field number.
     A field specification of `0' denotes the join field.  In most
     cases, the functionality of the `0' field spec may be reproduced
     using the explicit M.N that corresponds to the join field.
     However, when printing unpairable lines (using either of the `-a'
     or `-v' options), there is no way to specify the join field using
     M.N in FIELD-LIST if there are unpairable lines in both files.  To
     give `join' that functionality, POSIX invented the `0' field
     specification notation.
     The elements in FIELD-LIST are separated by commas or blanks.
     Multiple FIELD-LIST arguments can be given after a single `-o'
     option; the values of all lists given with `-o' are concatenated
     together.  All output lines - including those printed because of
     any -a or -v option - are subject to the specified FIELD-LIST.
`-t CHAR'
     Use character CHAR as the input and output field separator.
`-v FILE-NUMBER'
     Print a line for each unpairable line in file FILE-NUMBER (either
     `1' or `2'), instead of the normal output.
   In addition, when GNU `join' is invoked with exactly one argument,
options `--help' and `--version' are recognized.  *Note Common
options::.
File: textutils.info,  Node: Operating on characters,  Next: Opening the software toolbox,  Prev: Operating on fields within a line,  Up: Top
Operating on characters
***********************
   This commands operate on individual characters.
* Menu:
* tr invocation::               Translate, squeeze, and/or delete characters.
* expand invocation::           Convert tabs to spaces.
* unexpand invocation::         Convert spaces to tabs.
File: textutils.info,  Node: tr invocation,  Next: expand invocation,  Up: Operating on characters
`tr': Translate, squeeze, and/or delete characters
==================================================
   Synopsis:
     tr [OPTION]... SET1 [SET2]
   `tr' copies standard input to standard output, performing one of the
following operations:
   * translate, and optionally squeeze repeated characters in the
     result,
   * squeeze repeated characters,
   * delete characters,
   * delete characters, then squeeze repeated characters from the
     result.
   The SET1 and (if given) SET2 arguments define ordered sets of
characters, referred to below as SET1 and SET2.  These sets are the
characters of the input that `tr' operates on.  The `--complement'
(`-c') option replaces SET1 with its complement (all of the characters
that are not in SET1).
* Menu:
* Character sets::              Specifying sets of characters.
* Translating::                 Changing one characters to another.
* Squeezing::                   Squeezing repeats and deleting.
* Warnings in tr::              Warning messages.
File: textutils.info,  Node: Character sets,  Next: Translating,  Up: tr invocation
Specifying sets of characters
-----------------------------
   The format of the SET1 and SET2 arguments resembles the format of
regular expressions; however, they are not regular expressions, only
lists of characters.  Most characters simply represent themselves in
these strings, but the strings can contain the shorthands listed below,
for convenience.  Some of them can be used only in SET1 or SET2, as
noted below.
Backslash escapes.
     A backslash followed by a character not listed below causes an
     error message.
    `\a'
          Control-G,
    `\b'
          Control-H,
    `\f'
          Control-L,
    `\n'
          Control-J,
    `\r'
          Control-M,
    `\t'
          Control-I,
    `\v'
          Control-K,
    `\OOO'
          The character with the value given by OOO, which is 1 to 3
          octal digits,
    `\\'
          A backslash.
Ranges.
     The notation `M-N' expands to all of the characters from M through
     N, in ascending order.  M should collate before N; if it doesn't,
     an error results.  As an example, `0-9' is the same as
     `0123456789'.  Although GNU `tr' does not support the System V
     syntax that uses square brackets to enclose ranges, translations
     specified in that format will still work as long as the brackets
     in STRING1 correspond to identical brackets in STRING2.
Repeated characters.
     The notation `[C*N]' in SET2 expands to N copies of character C.
     Thus, `[y*6]' is the same as `yyyyyy'.  The notation `[C*]' in
     STRING2 expands to as many copies of C as are needed to make SET2
     as long as SET1.  If N begins with `0', it is interpreted in
     octal, otherwise in decimal.
Character classes.
     The notation `[:CLASS:]' expands to all of the characters in the
     (predefined) class CLASS.  The characters expand in no particular
     order, except for the `upper' and `lower' classes, which expand in
     ascending order.  When the `--delete' (`-d') and
     `--squeeze-repeats' (`-s') options are both given, any character
     class can be used in SET2.  Otherwise, only the character classes
     `lower' and `upper' are accepted in SET2, and then only if the
     corresponding character class (`upper' and `lower', respectively)
     is specified in the same relative position in SET1.  Doing this
     specifies case conversion.  The class names are given below; an
     error results when an invalid class name is given.
    `alnum'
          Letters and digits.
    `alpha'
          Letters.
    `blank'
          Horizontal whitespace.
    `cntrl'
          Control characters.
    `digit'
          Digits.
    `graph'
          Printable characters, not including space.
    `lower'
          Lowercase letters.
    `print'
          Printable characters, including space.
    `punct'
          Punctuation characters.
    `space'
          Horizontal or vertical whitespace.
    `upper'
          Uppercase letters.
    `xdigit'
          Hexadecimal digits.
Equivalence classes.
     The syntax `[=C=]' expands to all of the characters that are
     equivalent to C, in no particular order.  Equivalence classes are
     a relatively recent invention intended to support non-English
     alphabets.  But there seems to be no standard way to define them
     or determine their contents.  Therefore, they are not fully
     implemented in GNU `tr'; each character's equivalence class
     consists only of that character, which is of no particular use.
File: textutils.info,  Node: Translating,  Next: Squeezing,  Prev: Character sets,  Up: tr invocation
Translating
-----------
   `tr' performs translation when SET1 and SET2 are both given and the
`--delete' (`-d') option is not given.  `tr' translates each character
of its input that is in SET1 to the corresponding character in SET2.
Characters not in SET1 are passed through unchanged.  When a character
appears more than once in SET1 and the corresponding characters in SET2
are not all the same, only the final one is used.  For example, these
two commands are equivalent:
     tr aaa xyz
     tr a z
   A common use of `tr' is to convert lowercase characters to
uppercase.  This can be done in many ways.  Here are three of them:
     tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
     tr a-z A-Z
     tr '[:lower:]' '[:upper:]'
   When `tr' is performing translation, SET1 and SET2 typically have
the same length.  If SET1 is shorter than SET2, the extra characters at
the end of SET2 are ignored.
   On the other hand, making SET1 longer than SET2 is not portable;
POSIX.2 says that the result is undefined.  In this situation, BSD `tr'
pads SET2 to the length of SET1 by repeating the last character of SET2
as many times as necessary.  System V `tr' truncates SET1 to the length
of SET2.
   By default, GNU `tr' handles this case like BSD `tr'.  When the
`--truncate-set1' (`-t') option is given, GNU `tr' handles this case
like the System V `tr' instead.  This option is ignored for operations
other than translation.
   Acting like System V `tr' in this case breaks the relatively common
BSD idiom:
     tr -cs A-Za-z0-9 '\012'
because it converts only zero bytes (the first element in the
complement of SET1), rather than all non-alphanumerics, to newlines.
File: textutils.info,  Node: Squeezing,  Next: Warnings in tr,  Prev: Translating,  Up: tr invocation
Squeezing repeats and deleting
------------------------------
   When given just the `--delete' (`-d') option, `tr' removes any input
characters that are in SET1.
   When given just the `--squeeze-repeats' (`-s') option, `tr' replaces
each input sequence of a repeated character that is in SET1 with a
single occurrence of that character.
   When given both `--delete' and `--squeeze-repeats', `tr' first
performs any deletions using SET1, then squeezes repeats from any
remaining characters using SET2.
   The `--squeeze-repeats' option may also be used when translating, in
which case `tr' first performs translation, then squeezes repeats from
any remaining characters using SET2.
   Here are some examples to illustrate various combinations of options:
   * Remove all zero bytes:
          tr -d '\000'
   * Put all words on lines by themselves.  This converts all
     non-alphanumeric characters to newlines, then squeezes each string
     of repeated newlines into a single newline:
          tr -cs '[a-zA-Z0-9]' '[\n*]'
   * Convert each sequence of repeated newlines to a single newline:
          tr -s '\n'
File: textutils.info,  Node: Warnings in tr,  Prev: Squeezing,  Up: tr invocation
Warning messages
----------------
   Setting the environment variable `POSIXLY_CORRECT' turns off the
following warning and error messages, for strict compliance with
POSIX.2.  Otherwise, the following diagnostics are issued:
  1. When the `--delete' option is given but `--squeeze-repeats' is
     not, and SET2 is given, GNU `tr' by default prints a usage message
     and exits, because SET2 would not be used.  The POSIX
     specification says that SET2 must be ignored in this case.
     Silently ignoring arguments is a bad idea.
  2. When an ambiguous octal escape is given.  For example, `\400' is
     actually `\40' followed by the digit `0', because the value 400
     octal does not fit into a single byte.
   GNU `tr' does not provide complete BSD or System V compatibility.
For example, it is impossible to disable interpretation of the POSIX
constructs `[:alpha:]', `[=c=]', and `[c*10]'.  Also, GNU `tr' does not
delete zero bytes automatically, unlike traditional Unix versions,
which provide no way to preserve zero bytes.
File: textutils.info,  Node: expand invocation,  Next: unexpand invocation,  Prev: tr invocation,  Up: Operating on characters
`expand': Convert tabs to spaces
================================
   `expand' writes the contents of each given FILE, or standard input
if none are given or for a FILE of `-', to standard output, with tab
characters converted to the appropriate number of spaces.  Synopsis:
     expand [OPTION]... [FILE]...
   By default, `expand' converts all tabs to spaces.  It preserves
backspace characters in the output; they decrement the column count for
tab calculations.  The default action is equivalent to `-8' (set tabs
every 8 columns).
   The program accepts the following options.  Also see *Note Common
options::.
`-TAB1[,TAB2]...'
`-t TAB1[,TAB2]...'
`--tabs=TAB1[,TAB2]...'
     If only one tab stop is given, set the tabs TAB1 spaces apart
     (default is 8).  Otherwise, set the tabs at columns TAB1, TAB2,
     ... (numbered from 0), and replace any tabs beyond the last
     tabstop given with single spaces.  If the tabstops are specified
     with the `-t' or `--tabs' option, they can be separated by blanks
     as well as by commas.
`--initial'
     Only convert initial tabs (those that precede all non-space or
     non-tab characters) on each line to spaces.
File: textutils.info,  Node: unexpand invocation,  Prev: expand invocation,  Up: Operating on characters
`unexpand': Convert spaces to tabs
==================================
   `unexpand' writes the contents of each given FILE, or standard input
if none are given or for a FILE of `-', to standard output, with
strings of two or more space or tab characters converted to as many
tabs as possible followed by as many spaces as are needed.  Synopsis:
     unexpand [OPTION]... [FILE]...
   By default, `unexpand' converts only initial spaces and tabs (those
that precede all non space or tab characters) on each line.  It
preserves backspace characters in the output; they decrement the column
count for tab calculations.  By default, tabs are set at every 8th
column.
   The program accepts the following options.  Also see *Note Common
options::.
`-TAB1[,TAB2]...'
`-t TAB1[,TAB2]...'
`--tabs=TAB1[,TAB2]...'
     If only one tab stop is given, set the tabs TAB1 spaces apart
     instead of the default 8.  Otherwise, set the tabs at columns
     TAB1, TAB2, ... (numbered from 0), and leave spaces and tabs
     beyond the tabstops given unchanged.  If the tabstops are specified
     with the `-t' or `--tabs' option, they can be separated by blanks
     as well as by commas.  This option implies the `-a' option.
`--all'
     Convert all strings of two or more spaces or tabs, not just initial
     ones, to tabs.
File: textutils.info,  Node: Opening the software toolbox,  Next: Index,  Prev: Operating on characters,  Up: Top
Opening the software toolbox
****************************
   This chapter originally appeared in `Linux Journal', volume 1,
number 2, in the `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::
File: textutils.info,  Node: Toolbox introduction,  Next: I/O redirection,  Up: Opening the software toolbox
Toolbox introduction
====================
   This month's column is only peripherally related to the GNU Project,
in that it describes a number of the GNU tools on your Linux system and
how they might be used.  What it's really about is the "Software Tools"
philosophy of program development and usage.
   The software tools philosophy was an important and integral concept
in the initial design and development of Unix (of which Linux and GNU
are essentially clones).  Unfortunately, in the modern day press of
Internetworking and flashy GUIs, it seems to have fallen by the
wayside.  This is a shame, since it provides a powerful mental model
for solving many kinds of problems.
   Many people carry a Swiss Army knife around in their pants pockets
(or purse).  A Swiss Army knife is a handy tool to have: it has several
knife blades, a screwdriver, tweezers, toothpick, nail file, corkscrew,
and perhaps a number of other things on it.  For the everyday, small
miscellaneous jobs where you need a simple, general purpose tool, it's
just the thing.
   On the other hand, an experienced carpenter doesn't build a house
using a Swiss Army knife.  Instead, he has a toolbox chock full of
specialized tools--a saw, a hammer, a screwdriver, a plane, and so on.
And he knows exactly when and where to use each tool; you won't catch
him hammering nails with the handle of his screwdriver.
   The Unix developers at Bell Labs were all professional programmers
and trained computer scientists.  They had found that while a
one-size-fits-all program might appeal to a user because there's only
one program to use, in practice such programs are
  a. difficult to write,
  b. difficult to maintain and debug, and
  c. difficult to extend to meet new situations.
   Instead, they felt that programs should be specialized tools.  In
short, each program "should do one thing well."  No more and no less.
Such programs are simpler to design, write, and get right--they only do
one thing.
   Furthermore, they found that with the right machinery for hooking
programs together, that the whole was greater than the sum of the
parts.  By combining several special purpose programs, you could
accomplish a specific task that none of the programs was designed for,
and accomplish it much more quickly and easily than if you had to write
a special purpose program.  We will see some (classic) examples of this
further on in the column.  (An important additional point was that, if
necessary, take a detour and build any software tools you may need
first, if you don't already have something appropriate in the toolbox.)
File: textutils.info,  Node: I/O redirection,  Next: The `who' command,  Prev: Toolbox introduction,  Up: Opening the software toolbox
I/O redirection
===============
   Hopefully, you are familiar with the basics of I/O redirection in the
shell, in particular the concepts of "standard input," "standard
output," and "standard error".  Briefly, "standard input" is a data
source, where data comes from.  A program should not need to either
know or care if the data source is a disk file, a keyboard, a magnetic
tape, or even a punched card reader.  Similarly, "standard output" is a
data sink, where data goes to.  The program should neither know nor
care where this might be.  Programs that only read their standard
input, do something to the data, and then send it on, are called
"filters", by analogy to filters in a water pipeline.
   With the Unix shell, it's very easy to set up data pipelines:
     program_to_create_data | filter1 | .... | filterN > final.pretty.data
   We start out by creating the raw data; each filter applies some
successive transformation to the data, until by the time it comes out
of the pipeline, it is in the desired form.
   This is fine and good for standard input and standard output.  Where
does the standard error come in to play?  Well, think about `filter1' in
the pipeline above.  What happens if it encounters an error in the data
it sees?  If it writes an error message to standard output, it will just
disappear down the pipeline into `filter2''s input, and the user will
probably never see it.  So programs need a place where they can send
error messages so that the user will notice them.  This is standard
error, and it is usually connected to your console or window, even if
you have redirected standard output of your program away from your
screen.
   For filter programs to work together, the format of the data has to
be agreed upon.  The most straightforward and easiest format to use is
simply lines of text.  Unix data files are generally just streams of
bytes, with lines delimited by the ASCII LF (Line Feed) character,
conventionally called a "newline" in the Unix literature. (This is
`'\n'' if you're a C programmer.)  This is the format used by all the
traditional filtering programs.  (Many earlier operating systems had
elaborate facilities and special purpose programs for managing binary
data.  Unix has always shied away from such things, under the
philosophy that it's easiest to simply be able to view and edit your
data with a text editor.)
   OK, enough introduction. Let's take a look at some of the tools, and
then we'll see how to hook them together in interesting ways.   In the
following discussion, we will only present those command line options
that interest us.  As you should always do, double check your system
documentation for the full story.
File: textutils.info,  Node: The `who' command,  Next: The `cut' command,  Prev: I/O redirection,  Up: Opening the software toolbox
The `who' command
=================
   The first program is the `who' command.  By itself, it generates a
list of the users who are currently logged in.  Although I'm writing
this on a single-user system, we'll pretend that several people are
logged in:
     $ who
     arnold   console Jan 22 19:57
     miriam   ttyp0   Jan 23 14:19(:0.0)
     bill     ttyp1   Jan 21 09:32(:0.0)
     arnold   ttyp2   Jan 23 20:48(:0.0)
   Here, the `$' is the usual shell prompt, at which I typed `who'.
There are three people logged in, and I am logged in twice.  On
traditional Unix systems, user names are never more than eight
characters long.  This little bit of trivia will be useful later.  The
output of `who' is nice, but the data is not all that exciting.
File: textutils.info,  Node: The `cut' command,  Next: The `sort' command,  Prev: The `who' command,  Up: Opening the software toolbox
The `cut' command
=================
   The next program we'll look at is the `cut' command.  This program
cuts out columns or fields of input data.  For example, we can tell it
to print just the login name and full name from the `/etc/passwd file'.
The `/etc/passwd' file has seven fields, separated by colons:
     arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/ksh
   To get the first and fifth fields, we would use cut like this:
     $ cut -d: -f1,5 /etc/passwd
     root:Operator
     ...
     arnold:Arnold D. Robbins
     miriam:Miriam A. Robbins
     ...
   With the `-c' option, `cut' will cut out specific characters (i.e.,
columns) in the input lines.  This command looks like it might be
useful for data filtering.
File: textutils.info,  Node: The `sort' command,  Next: The `uniq' command,  Prev: The `cut' command,  Up: Opening the software toolbox
The `sort' command
==================
   Next we'll look at the `sort' command.  This is one of the most
powerful commands on a Unix-style system; one that you will often find
yourself using when setting up fancy data plumbing. The `sort' command
reads and sorts each file named on the command line.  It then merges
the sorted data and writes it to standard output.  It will read
standard input if no files are given on the command line (thus making
it into a filter).  The sort is based on the machine collating sequence
(ASCII) or based on  user-supplied ordering criteria.
File: textutils.info,  Node: The `uniq' command,  Next: Putting the tools together,  Prev: The `sort' command,  Up: Opening the software toolbox
The `uniq' command
==================
   Finally (at least for now), we'll look at the `uniq' program.  When
sorting data, you will often end up with duplicate lines, lines that
are identical.  Usually, all you need is one instance of each line.
This is where `uniq' comes in. The `uniq' program reads its standard
input, which it expects to be sorted.  It only prints out one copy of
each duplicated line.  It does have several options.  Later on, we'll
use the `-c' option, which prints each unique line, preceded by a count
of the number of times that line occurred in the input.
File: textutils.info,  Node: Putting the tools together,  Prev: The `uniq' command,  Up: Opening the software toolbox
Putting the tools together
==========================
   Now, let's suppose this is a large BBS system with dozens of users
logged in.  The management wants the SysOp to write a program that will
generate a sorted list of logged in users.  Furthermore, even if a user
is logged in multiple times, his or her name should only show up in the
output once.
   The SysOp could sit down with the system documentation and write a C
program that did this. It would take perhaps a couple of hundred lines
of code and about two hours to write it, test it, and debug it.
However, knowing the software toolbox, the SysOp can instead start out
by generating just a list of logged on users:
     $ who | cut -c1-8
     arnold
     miriam
     bill
     arnold
   Next, sort the list:
     $ who | cut -c1-8 | sort
     arnold
     arnold
     bill
     miriam
   Finally, run the sorted list through `uniq', to weed out duplicates:
     $ who | cut -c1-8 | sort | uniq
     arnold
     bill
     miriam
   The `sort' command actually has a `-u' option that does what `uniq'
does. However, `uniq' has other uses for which one cannot substitute
`sort -u'.
   The SysOp puts this pipeline into a shell script, and makes it
available for all the users on the system:
     # cat > /usr/local/bin/listusers
     who | cut -c1-8 | sort | uniq
     ^D
     # chmod +x /usr/local/bin/listusers
   There are four major points to note here.  First, with just four
programs, on one command line, the SysOp was able to save about two
hours worth of work.  Furthermore, the shell pipeline is just about as
efficient as the C program would be, and it is much more efficient in
terms of programmer time.  People time is much more expensive than
computer time, and in our modern "there's never enough time to do
everything" society, saving two hours of programmer time is no mean
feat.
   Second, it is also important to emphasize that with the
*combination* of the tools, it is possible to do a special purpose job
never imagined by the authors of the individual programs.
   Third, it is also valuable to build up your pipeline in stages, as
we did here.  This allows you to view the data at each stage in the
pipeline, which helps you acquire the confidence that you are indeed
using these tools correctly.
   Finally, by bundling the pipeline in a shell script, other users can
use your command, without having to remember the fancy plumbing you set
up for them. In terms of how you run them, shell scripts and compiled
programs are indistinguishable.
   After the previous warm-up exercise, we'll look at two additional,
more complicated pipelines.  For them, we need to introduce two more
tools.
   The first is the `tr' command, which stands for "transliterate." The
`tr' command works on a character-by-character basis, changing
characters. Normally it is used for things like mapping upper case to
lower case:
     $ echo ThIs ExAmPlE HaS MIXED case! | tr '[A-Z]' '[a-z]'
     this example has mixed case!
   There are several options of interest:
     work on the complement of the listed characters, i.e., operations
     apply to characters not in the given set
     delete characters in the first set from the output
     squeeze repeated characters in the output into just one character.
   We will be using all three options in a moment.
   The other command we'll look at is `comm'.  The `comm' command takes
two sorted input files as input data, and prints out the files' lines
in three columns.  The output columns are the data lines unique to the
first file, the data lines unique to the second file, and the data
lines that are common to both.  The `-1', `-2', and `-3' command line
options omit the respective columns. (This is non-intuitive and takes a
little getting used to.)  For example:
     $ cat f1
     11111
     22222
     33333
     44444
     $ cat f2
     00000
     22222
     33333
     55555
     $ comm f1 f2
             00000
     11111
                     22222
                     33333
     44444
             55555
   The single dash as a filename tells `comm' to read standard input
instead of a regular file.
   Now we're ready to build a fancy pipeline.  The first application is
a word frequency counter.  This helps an author determine if he or she
is over-using certain words.
   The first step is to change the case of all the letters in our input
file to one case.  "The" and "the" are the same word when doing
counting.
     $ tr '[A-Z]' '[a-z]' < whats.gnu | ...
   The next step is to get rid of punctuation.  Quoted words and
unquoted words should be treated identically; it's easiest to just get
the punctuation out of the way.
     $ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' | ...
   The second `tr' command operates on the complement of the listed
characters, which are all the letters, the digits, the underscore, and
the blank.  The `\012' represents the newline character; it has to be
left alone.  (The ASCII TAB character should also be included for good
measure in a production script.)
   At this point, we have data consisting of words separated by blank
space.  The words only contain alphanumeric characters (and the
underscore).  The next step is break the data apart so that we have one
word per line. This makes the counting operation much easier, as we
will see shortly.
     $ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' |
     > tr -s '[ ]' '\012' | ...
   This command turns blanks into newlines.  The `-s' option squeezes
multiple newline characters in the output into just one.  This helps us
avoid blank lines. (The `>' is the shell's "secondary prompt." This is
what the shell prints when it notices you haven't finished typing in
all of a command.)
   We now have data consisting of one word per line, no punctuation,
all one case.  We're ready to count each word:
     $ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' |
     > tr -s '[ ]' '\012' | sort | uniq -c | ...
   At this point, the data might look something like this:
       60 a
        2 able
        6 about
        1 above
        2 accomplish
        1 acquire
        1 actually
        2 additional
   The output is sorted by word, not by count!  What we want is the most
frequently used words first.  Fortunately, this is easy to accomplish,
with the help of two more `sort' options:
     do a numeric sort, not an ASCII one
     reverse the order of the sort
   The final pipeline looks like this:
     $ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' |
     > tr -s '[ ]' '\012' | sort | uniq -c | sort -nr
      156 the
       60 a
       58 to
       51 of
       51 and
      ...
   Whew!  That's a lot to digest.  Yet, the same principles apply. With
six commands, on two lines (really one long one split for convenience),
we've created a program that does something interesting and useful, in
much less time than we could have written a C program to do the same
thing.
   A minor modification to the above pipeline can give us a simple
spelling checker!  To determine if you've spelled a word correctly, all
you have to do is look it up in a dictionary.  If it is not there, then
chances are that your spelling is incorrect.  So, we need a dictionary.
If you have the Slackware Linux distribution, you have the file
`/usr/lib/ispell/ispell.words', which is a sorted, 38,400 word
dictionary.
   Now, how to compare our file with the dictionary?  As before, we
generate a sorted list of words, one per line:
     $ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' |
     > tr -s '[ ]' '\012' | sort -u | ...
   Now, all we need is a list of words that are *not* in the
dictionary.  Here is where the `comm' command comes in.
     $ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' |
     > tr -s '[ ]' '\012' | sort -u |
     > comm -23 - /usr/lib/ispell/ispell.words
   The `-2' and `-3' options eliminate lines that are only in the
dictionary (the second file), and lines that are in both files.  Lines
only in the first file (standard input, our stream of words), are words
that are not in the dictionary.  These are likely candidates for
spelling errors.  This pipeline was the first cut at a production
spelling checker on Unix.
   There are some other tools that deserve brief mention.
`grep'
     search files for text that matches a regular expression
`egrep'
     like `grep', but with more powerful regular expressions
     count lines, words, characters
`tee'
     a T-fitting for data pipes, copies data to files and to standard
     output
`sed'
     the stream editor, an advanced tool
`awk'
     a data manipulation language, another advanced tool
   The software tools philosophy also espoused the following bit of
advice: "Let someone else do the hard part." This means, take something
that gives you most of what you need, and then massage it the rest of
the way until it's in the form that you want.
   To summarize:
  1. Each program should do one thing well. No more, no less.
  2. Combining programs with appropriate plumbing leads to results where
     the whole is greater than the sum of the parts.  It also leads to
     novel uses of programs that the authors might never have imagined.
  3. Programs should never print extraneous header or trailer data,
     since these could get sent on down a pipeline. (A point we didn't
     mention earlier.)
  4. Let someone else do the hard part.
  5. Know your toolbox! Use each program appropriately. If you don't
     have an appropriate tool, build one.
   As of this writing, all the programs we've discussed are available
via anonymous `ftp' from `prep.ai.mit.edu' as
`/pub/gnu/textutils-1.9.tar.gz' directory.(1)
   None of what I have presented in this column is new. The Software
Tools philosophy was first introduced in the book `Software Tools', by
Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
This book showed how to write and use software tools.   It was written
in 1976, using a preprocessor for FORTRAN named `ratfor' (RATional
FORtran).  At the time, C was not as ubiquitous as it is now; FORTRAN
was.  The last chapter presented a `ratfor' to FORTRAN processor,
written in `ratfor'. `ratfor' looks an awful lot like C; if you know C,
you won't have any problem following the code.
   In 1981, the book was updated and made available as `Software Tools
in Pascal' (Addison-Wesley, ISBN 0-201-10342-7).  Both books remain in
print, and are well worth reading if you're a programmer.  They
certainly made a major change in how I view programming.
   Initially, the programs in both books were available (on 9-track
tape) from Addison-Wesley.  Unfortunately, this is no longer the case,
although you might be able to find copies floating around the Internet.
For a number of years, there was an active Software Tools Users Group,
whose members had ported the original `ratfor' programs to essentially
every computer system with a FORTRAN compiler.  The popularity of the
group waned in the middle '80s as Unix began to spread beyond
universities.
   With the current proliferation of GNU code and other clones of Unix
programs, these programs now receive little attention; modern C
versions are much more efficient and do more than these programs do.
Nevertheless, as exposition of good programming style, and evangelism
for a still-valuable philosophy, these books are unparalleled, and I
recommend them highly.
   Acknowledgment: I would like to express my gratitude to Brian
Kernighan of Bell Labs, the original Software Toolsmith, for reviewing
this column.
   ---------- Footnotes ----------
   (1)  Version 1.9 was current when this column was written. Check the
nearest GNU archive for the current version.
File: textutils.info,  Node: Index,  Prev: Opening the software toolbox,  Up: Top
Index
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* telephone directory order:             sort invocation.
* text input files:                      md5sum invocation.
* text utilities:                        Top.
* text, reformatting:                    fmt invocation.
* TMPDIR:                                sort invocation.
* total counts:                          wc invocation.
* tr:                                    tr invocation.
* translating characters:                Translating.
* type size:                             od invocation.
* unexpand:                              unexpand invocation.
* uniq:                                  uniq invocation.
* uniqify files:                         uniq invocation.
* uniqifying output:                     sort invocation.
* unique lines, outputting:              uniq invocation.
* unprintable characters, ignoring:      sort invocation.
* upper:                                 Character sets.
* utilities for text handling:           Top.
* verifying MD5 checksums:               md5sum invocation.
* version number, finding:               Common options.
* wc:                                    wc invocation.
* word count:                            wc invocation.
* wrapping long input lines:             fold invocation.
* xdigit:                                Character sets.
Tag Table:
Node: Top
Node: Introduction
Node: Common options
Node: Output of entire files
Node: cat invocation
Node: tac invocation
Node: nl invocation
Node: od invocation
11836
Node: Formatting file contents
17401
Node: fmt invocation
17851
Node: pr invocation
20555
Node: fold invocation
27596
Node: Output of parts of files
28838
Node: head invocation
29345
Node: tail invocation
30754
Node: split invocation
33136
Node: csplit invocation
34759
Node: Summarizing files
38796
Node: wc invocation
39320
Node: sum invocation
40482
Node: cksum invocation
41795
Node: md5sum invocation
42846
Node: Operating on sorted files
46043
Node: sort invocation
46465
Node: uniq invocation
57538
Node: comm invocation
59219
Node: Operating on fields within a line
60023
Node: cut invocation
60423
Node: paste invocation
62130
Node: join invocation
62977
Node: Operating on characters
66298
Node: tr invocation
66744
Node: Character sets
67861
Node: Translating
71457
Node: Squeezing
73254
Node: Warnings in tr
74491
Node: expand invocation
75624
Node: unexpand invocation
76941
Node: Opening the software toolbox
78376
Node: Toolbox introduction
78868
Node: I/O redirection
81590
Node: The `who' command
84428
Node: The `cut' command
85320
Node: The `sort' command
86201
Node: The `uniq' command
86918
Node: Putting the tools together
87651
Node: Index
99607
End Tag Table