Provided by: grep_2.10-1_amd64 bug

NAME

       grep, egrep, fgrep, rgrep - print lines matching a pattern

SYNOPSIS

       grep [OPTIONS] PATTERN [FILE...]
       grep [OPTIONS] [-e PATTERN | -f FILE] [FILE...]

DESCRIPTION

       grep  searches  the  named  input  FILEs (or standard input if no files are named, or if a
       single hyphen-minus (-) is given as file name) for lines containing a match to  the  given
       PATTERN.  By default, grep prints the matching lines.

       In  addition,  three  variant programs egrep, fgrep and rgrep are available.  egrep is the
       same as grep -E.  fgrep is the same as grep -F.  rgrep is the  same  as  grep -r.   Direct
       invocation  as  either  egrep  or fgrep is deprecated, but is provided to allow historical
       applications that rely on them to run unmodified.

OPTIONS

   Generic Program Information
       --help Print a usage message briefly summarizing these command-line options and  the  bug-
              reporting address, then exit.

       -V, --version
              Print  the  version  number  of  grep  to the standard output stream.  This version
              number should be included in all bug reports (see below).

   Matcher Selection
       -E, --extended-regexp
              Interpret PATTERN as an extended regular  expression  (ERE,  see  below).   (-E  is
              specified by POSIX.)

       -F, --fixed-strings
              Interpret  PATTERN  as a list of fixed strings, separated by newlines, any of which
              is to be matched.  (-F is specified by POSIX.)

       -G, --basic-regexp
              Interpret PATTERN as a basic regular expression (BRE,  see  below).   This  is  the
              default.

       -P, --perl-regexp
              Interpret  PATTERN  as a Perl regular expression (PCRE, see below).  This is highly
              experimental and grep -P may warn of unimplemented features.

   Matching Control
       -e PATTERN, --regexp=PATTERN
              Use PATTERN as the pattern.  This can be used to specify multiple search  patterns,
              or to protect a pattern beginning with a hyphen (-).  (-e is specified by POSIX.)

       -f FILE, --file=FILE
              Obtain  patterns  from  FILE, one per line.  The empty file contains zero patterns,
              and therefore matches nothing.  (-f is specified by POSIX.)

       -i, --ignore-case
              Ignore case distinctions in both the PATTERN and the input files.  (-i is specified
              by POSIX.)

       -v, --invert-match
              Invert  the  sense  of matching, to select non-matching lines.  (-v is specified by
              POSIX.)

       -w, --word-regexp
              Select only those lines containing matches that form whole words.  The test is that
              the  matching substring must either be at the beginning of the line, or preceded by
              a non-word constituent character.  Similarly, it must be either at the end  of  the
              line  or followed by a non-word constituent character.  Word-constituent characters
              are letters, digits, and the underscore.

       -x, --line-regexp
              Select only those matches that exactly match the whole line.  (-x is  specified  by
              POSIX.)

       -y     Obsolete synonym for -i.

   General Output Control
       -c, --count
              Suppress  normal  output;  instead  print  a count of matching lines for each input
              file.  With the -v, --invert-match option (see below),  count  non-matching  lines.
              (-c is specified by POSIX.)

       --color[=WHEN], --colour[=WHEN]
              Surround  the  matched  (non-empty)  strings,  matching  lines, context lines, file
              names, line numbers, byte offsets, and separators (for fields and groups of context
              lines)  with escape sequences to display them in color on the terminal.  The colors
              are defined by the environment variable GREP_COLORS.   The  deprecated  environment
              variable  GREP_COLOR  is  still  supported, but its setting does not have priority.
              WHEN is never, always, or auto.

       -L, --files-without-match
              Suppress normal output; instead print the name of each input  file  from  which  no
              output  would  normally  have  been  printed.   The scanning will stop on the first
              match.

       -l, --files-with-matches
              Suppress normal output; instead print the name of each input file from which output
              would  normally have been printed.  The scanning will stop on the first match.  (-l
              is specified by POSIX.)

       -m NUM, --max-count=NUM
              Stop reading a file after NUM matching lines.  If the input is standard input  from
              a  regular  file, and NUM matching lines are output, grep ensures that the standard
              input is positioned to just after the last matching line before exiting, regardless
              of  the  presence  of  trailing  context  lines.  This enables a calling process to
              resume a search.  When grep stops after NUM matching lines, it outputs any trailing
              context  lines.  When the -c or --count option is also used, grep does not output a
              count greater than NUM.  When the -v or --invert-match option is  also  used,  grep
              stops after outputting NUM non-matching lines.

       -o, --only-matching
              Print only the matched (non-empty) parts of a matching line, with each such part on
              a separate output line.

       -q, --quiet, --silent
              Quiet; do not write anything to standard output.  Exit immediately with zero status
              if  any  match  is  found,  even  if  an  error  was  detected.  Also see the -s or
              --no-messages option.  (-q is specified by POSIX.)

       -s, --no-messages
              Suppress error messages about nonexistent or unreadable files.   Portability  note:
              unlike  GNU grep, 7th Edition Unix grep did not conform to POSIX, because it lacked
              -q and its -s option behaved like GNU grep's -q option.  USG-style grep also lacked
              -q  but  its  -s option behaved like GNU grep.  Portable shell scripts should avoid
              both -q and -s and should redirect standard and error output to /dev/null  instead.
              (-s is specified by POSIX.)

   Output Line Prefix Control
       -b, --byte-offset
              Print the 0-based byte offset within the input file before each line of output.  If
              -o (--only-matching) is specified, print the offset of the matching part itself.

       -H, --with-filename
              Print the file name for each match.  This is the default when there  is  more  than
              one file to search.

       -h, --no-filename
              Suppress  the prefixing of file names on output.  This is the default when there is
              only one file (or only standard input) to search.

       --label=LABEL
              Display input actually coming from standard input as input coming from file  LABEL.
              This is especially useful when implementing tools like zgrep, e.g., gzip -cd foo.gz
              | grep --label=foo -H something.  See also the -H option.

       -n, --line-number
              Prefix each line of output with the 1-based line number within its input file.  (-n
              is specified by POSIX.)

       -T, --initial-tab
              Make  sure  that  the first character of actual line content lies on a tab stop, so
              that the alignment of tabs looks normal.  This is useful with options  that  prefix
              their  output  to  the  actual  content:  -H,-n,  and  -b.  In order to improve the
              probability that lines from a single file will all start at the same  column,  this
              also causes the line number and byte offset (if present) to be printed in a minimum
              size field width.

       -u, --unix-byte-offsets
              Report Unix-style byte offsets.  This switch causes grep to report byte offsets  as
              if  the  file  were  a Unix-style text file, i.e., with CR characters stripped off.
              This will produce results identical to running grep on a Unix machine.  This option
              has  no  effect  unless -b option is also used; it has no effect on platforms other
              than MS-DOS and MS-Windows.

       -Z, --null
              Output a zero byte (the ASCII NUL character) instead of the character that normally
              follows  a  file  name.   For example, grep -lZ outputs a zero byte after each file
              name instead of the usual newline.  This option makes the output unambiguous,  even
              in  the  presence  of file names containing unusual characters like newlines.  This
              option can be used with commands like find -print0, perl -0, sort -z, and xargs  -0
              to process arbitrary file names, even those that contain newline characters.

   Context Line Control
       -A NUM, --after-context=NUM
              Print NUM lines of trailing context after matching lines.  Places a line containing
              a group separator (--) between contiguous  groups  of  matches.   With  the  -o  or
              --only-matching option, this has no effect and a warning is given.

       -B NUM, --before-context=NUM
              Print NUM lines of leading context before matching lines.  Places a line containing
              a group separator (--) between contiguous  groups  of  matches.   With  the  -o  or
              --only-matching option, this has no effect and a warning is given.

       -C NUM, -NUM, --context=NUM
              Print NUM lines of output context.  Places a line containing a group separator (--)
              between contiguous groups of matches.  With the -o or --only-matching option,  this
              has no effect and a warning is given.

   File and Directory Selection
       -a, --text
              Process   a   binary   file  as  if  it  were  text;  this  is  equivalent  to  the
              --binary-files=text option.

       --binary-files=TYPE
              If the first few bytes of a file indicate  that  the  file  contains  binary  data,
              assume  that  the  file  is  of  type  TYPE.   By default, TYPE is binary, and grep
              normally outputs either a one-line message saying that a binary file matches, or no
              message if there is no match.  If TYPE is without-match, grep assumes that a binary
              file does not match; this is equivalent to the -I option.  If TYPE  is  text,  grep
              processes  a  binary  file as if it were text; this is equivalent to the -a option.
              Warning: grep --binary-files=text might output binary garbage, which can have nasty
              side effects if the output is a terminal and if the terminal driver interprets some
              of it as commands.

       -D ACTION, --devices=ACTION
              If an input file is a device, FIFO  or  socket,  use  ACTION  to  process  it.   By
              default,  ACTION  is  read,  which means that devices are read just as if they were
              ordinary files.  If ACTION is skip, devices are silently skipped.

       -d ACTION, --directories=ACTION
              If an input file is a directory, use ACTION to process it.  By default,  ACTION  is
              read,  which  means  that directories are read just as if they were ordinary files.
              If ACTION is skip, directories are silently skipped.  If ACTION  is  recurse,  grep
              reads  all  files  under  each directory, recursively; this is equivalent to the -r
              option.

       --exclude=GLOB
              Skip files whose base name matches GLOB (using  wildcard  matching).   A  file-name
              glob  can use *, ?, and [...]  as wildcards, and \ to quote a wildcard or backslash
              character literally.

       --exclude-from=FILE
              Skip files whose base name matches any of the file-name globs read from FILE (using
              wildcard matching as described under --exclude).

       --exclude-dir=DIR
              Exclude directories matching the pattern DIR from recursive searches.

       -I     Process a binary file as if it did not contain matching data; this is equivalent to
              the --binary-files=without-match option.

       --include=GLOB
              Search only files  whose  base  name  matches  GLOB  (using  wildcard  matching  as
              described under --exclude).

       -R, -r, --recursive
              Read  all  files  under  each  directory, recursively; this is equivalent to the -d
              recurse option.

   Other Options
       --line-buffered
              Use line buffering on output.  This can cause a performance penalty.

       --mmap If possible, use the mmap(2) system call to read  input,  instead  of  the  default
              read(2)  system  call.   In  some  situations,  --mmap  yields  better performance.
              However, --mmap can cause undefined behavior (including core  dumps)  if  an  input
              file shrinks while grep is operating, or if an I/O error occurs.

       -U, --binary
              Treat the file(s) as binary.  By default, under MS-DOS and MS-Windows, grep guesses
              the file type by looking at the contents of the first 32KB read from the file.   If
              grep decides the file is a text file, it strips the CR characters from the original
              file  contents  (to  make  regular  expressions  with  ^  and  $  work  correctly).
              Specifying  -U overrules this guesswork, causing all files to be read and passed to
              the matching mechanism verbatim; if the file is a text file with CR/LF pairs at the
              end  of  each  line, this will cause some regular expressions to fail.  This option
              has no effect on platforms other than MS-DOS and MS-Windows.

       -z, --null-data
              Treat the input as a set of lines, each terminated by a zero byte  (the  ASCII  NUL
              character)  instead of a newline.  Like the -Z or --null option, this option can be
              used with commands like sort -z to process arbitrary file names.

REGULAR EXPRESSIONS

       A regular expression is a pattern that describes a set of  strings.   Regular  expressions
       are  constructed  analogously  to  arithmetic  expressions,  by using various operators to
       combine smaller expressions.

       grep understands three different versions of regular  expression  syntax:  “basic”  (BRE),
       “extended”  (ERE)  and  “perl”  (PRCE).  In  GNU grep, there is no difference in available
       functionality between basic  and  extended  syntaxes.   In  other  implementations,  basic
       regular  expressions  are  less  powerful.   The following description applies to extended
       regular expressions; differences for basic regular expressions are summarized  afterwards.
       Perl   regular   expressions   give   additional  functionality,  and  are  documented  in
       pcresyntax(3) and pcrepattern(3), but may not be available on every system.

       The fundamental building blocks are the regular expressions that match a single character.
       Most  characters,  including  all  letters  and digits, are regular expressions that match
       themselves.  Any meta-character with special meaning may be quoted by preceding it with  a
       backslash.

       The period . matches any single character.

   Character Classes and Bracket Expressions
       A  bracket  expression is a list of characters enclosed by [ and ].  It matches any single
       character in that list; if the first character of the list is the caret ^ then it  matches
       any  character  not in the list.  For example, the regular expression [0123456789] matches
       any single digit.

       Within a bracket expression, a range expression consists of two characters separated by  a
       hyphen.  It matches any single character that sorts between the two characters, inclusive,
       using the locale's collating sequence and character set.  For example, in  the  default  C
       locale,  [a-d] is equivalent to [abcd].  Many locales sort characters in dictionary order,
       and in these locales [a-d] is typically not equivalent to [abcd]; it might  be  equivalent
       to   [aBbCcDd],  for  example.   To  obtain  the  traditional  interpretation  of  bracket
       expressions, you can use the C locale by setting the LC_ALL environment  variable  to  the
       value C.

       Finally, certain named classes of characters are predefined within bracket expressions, as
       follows.  Their names are self explanatory, and they are [:alnum:], [:alpha:],  [:cntrl:],
       [:digit:],   [:graph:],   [:lower:],   [:print:],  [:punct:],  [:space:],  [:upper:],  and
       [:xdigit:].  For example, [[:alnum:]] means the character class of numbers and letters  in
       the  current locale. In the C locale and ASCII character set encoding, this is the same as
       [0-9A-Za-z].  (Note that the brackets in these class names are part of the symbolic names,
       and must be included in addition to the brackets delimiting the bracket expression.)  Most
       meta-characters lose their special meaning  inside  bracket  expressions.   To  include  a
       literal ] place it first in the list.  Similarly, to include a literal ^ place it anywhere
       but first.  Finally, to include a literal - place it last.

   Anchoring
       The caret ^ and the dollar sign $ are meta-characters that respectively  match  the  empty
       string at the beginning and end of a line.

   The Backslash Character and Special Expressions
       The  symbols  \<  and \> respectively match the empty string at the beginning and end of a
       word.  The symbol \b matches the empty string at the edge of a word, and  \B  matches  the
       empty  string  provided  it's  not  at the edge of a word.  The symbol \w is a synonym for
       [[:alnum:]] and \W is a synonym for [^[:alnum:]].

   Repetition
       A regular expression may be followed by one of several repetition operators:
       ?      The preceding item is optional and matched at most once.
       *      The preceding item will be matched zero or more times.
       +      The preceding item will be matched one or more times.
       {n}    The preceding item is matched exactly n times.
       {n,}   The preceding item is matched n or more times.
       {n,m}  The preceding item is matched at least n times, but not more than m times.

   Concatenation
       Two regular expressions may be concatenated; the resulting regular expression matches  any
       string  formed  by  concatenating  two substrings that respectively match the concatenated
       expressions.

   Alternation
       Two regular expressions may be joined by the  infix  operator  |;  the  resulting  regular
       expression matches any string matching either alternate expression.

   Precedence
       Repetition  takes  precedence  over  concatenation,  which  in  turn takes precedence over
       alternation.  A whole  expression  may  be  enclosed  in  parentheses  to  override  these
       precedence rules and form a subexpression.

   Back References and Subexpressions
       The back-reference \n, where n is a single digit, matches the substring previously matched
       by the nth parenthesized subexpression of the regular expression.

   Basic vs Extended Regular Expressions
       In basic regular expressions the meta-characters ?, +, {, |, (, and ) lose  their  special
       meaning; instead use the backslashed versions \?, \+, \{, \|, \(, and \).

       Traditional  egrep  did  not  support the { meta-character, and some egrep implementations
       support \{ instead, so portable scripts should avoid { in grep -E patterns and should  use
       [{] to match a literal {.

       GNU  grep -E attempts to support traditional usage by assuming that { is not special if it
       would be the start of  an  invalid  interval  specification.   For  example,  the  command
       grep -E '{1'  searches for the two-character string {1 instead of reporting a syntax error
       in the regular expression.  POSIX.2 allows this behavior as  an  extension,  but  portable
       scripts should avoid it.

ENVIRONMENT VARIABLES

       The behavior of grep is affected by the following environment variables.

       The  locale  for category LC_foo is specified by examining the three environment variables
       LC_ALL, LC_foo, LANG, in that order.  The first of these variables that is  set  specifies
       the  locale.  For example, if LC_ALL is not set, but LC_MESSAGES is set to pt_BR, then the
       Brazilian Portuguese locale is used for the LC_MESSAGES category.  The C locale is used if
       none of these environment variables are set, if the locale catalog is not installed, or if
       grep was not compiled with national language support (NLS).

       GREP_OPTIONS
              This variable specifies default options to be  placed  in  front  of  any  explicit
              options.    For   example,   if   GREP_OPTIONS   is   '--binary-files=without-match
              --directories=skip', grep behaves as if  the  two  options  --binary-files=without-
              match  and  --directories=skip  had  been  specified  before  any explicit options.
              Option specifications are separated by whitespace.  A backslash  escapes  the  next
              character,  so  it  can  be  used  to  specify an option containing whitespace or a
              backslash.

       GREP_COLOR
              This variable specifies the color used to highlight matched (non-empty)  text.   It
              is  deprecated  in  favor  of GREP_COLORS, but still supported.  The mt, ms, and mc
              capabilities of GREP_COLORS have priority over it.  It can only specify  the  color
              used to highlight the matching non-empty text in any matching line (a selected line
              when the -v  command-line  option  is  omitted,  or  a  context  line  when  -v  is
              specified).   The  default  is 01;31, which means a bold red foreground text on the
              terminal's default background.

       GREP_COLORS
              Specifies the colors and other attributes used to highlight various  parts  of  the
              output.   Its  value  is  a  colon-separated  list of capabilities that defaults to
              ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36  with  the  rv  and  ne   boolean
              capabilities omitted (i.e., false).  Supported capabilities are as follows.

              sl=    SGR  substring  for  whole  selected lines (i.e., matching lines when the -v
                     command-line option is omitted, or non-matching lines when -v is specified).
                     If however the boolean rv capability and the -v command-line option are both
                     specified, it applies to context matching lines  instead.   The  default  is
                     empty (i.e., the terminal's default color pair).

              cx=    SGR  substring for whole context lines (i.e., non-matching lines when the -v
                     command-line option is omitted, or matching lines when -v is specified).  If
                     however  the  boolean  rv capability and the -v command-line option are both
                     specified, it applies to selected non-matching lines instead.   The  default
                     is empty (i.e., the terminal's default color pair).

              rv     Boolean  value  that  reverses  (swaps)  the  meanings  of  the  sl= and cx=
                     capabilities when the -v command-line option is specified.  The  default  is
                     false (i.e., the capability is omitted).

              mt=01;31
                     SGR  substring  for  matching  non-empty  text in any matching line (i.e., a
                     selected line when the -v command-line option is omitted, or a context  line
                     when  -v  is specified).  Setting this is equivalent to setting both ms= and
                     mc= at once to the same value.  The default is a bold  red  text  foreground
                     over the current line background.

              ms=01;31
                     SGR substring for matching non-empty text in a selected line.  (This is only
                     used when the -v command-line option is omitted.)  The effect of the sl= (or
                     cx=  if  rv) capability remains active when this kicks in.  The default is a
                     bold red text foreground over the current line background.

              mc=01;31
                     SGR substring for matching non-empty text in a context line.  (This is  only
                     used  when  the -v command-line option is specified.)  The effect of the cx=
                     (or sl= if rv) capability remains active when this kicks in.  The default is
                     a bold red text foreground over the current line background.

              fn=35  SGR  substring  for file names prefixing any content line.  The default is a
                     magenta text foreground over the terminal's default background.

              ln=32  SGR substring for line numbers prefixing any content line.  The default is a
                     green text foreground over the terminal's default background.

              bn=32  SGR substring for byte offsets prefixing any content line.  The default is a
                     green text foreground over the terminal's default background.

              se=36  SGR substring for separators that are inserted between selected line  fields
                     (:),  between context line fields, (-), and between groups of adjacent lines
                     when nonzero context  is  specified  (--).   The  default  is  a  cyan  text
                     foreground over the terminal's default background.

              ne     Boolean  value that prevents clearing to the end of line using Erase in Line
                     (EL) to Right (\33[K) each time a colorized item ends.  This  is  needed  on
                     terminals on which EL is not supported.  It is otherwise useful on terminals
                     for which the back_color_erase (bce) boolean terminfo  capability  does  not
                     apply,  when  the  chosen  highlight colors do not affect the background, or
                     when EL is too slow or causes too much flicker.  The default is false (i.e.,
                     the capability is omitted).

              Note  that boolean capabilities have no =...  part.  They are omitted (i.e., false)
              by default and become true when specified.

              See the Select Graphic Rendition (SGR) section in the  documentation  of  the  text
              terminal  that  is  used  for  permitted  values  and  their  meaning  as character
              attributes.  These substring values are integers in decimal representation and  can
              be  concatenated  with semicolons.  grep takes care of assembling the result into a
              complete SGR sequence (\33[...m).  Common values to concatenate include 1 for bold,
              4 for underline, 5 for blink, 7 for inverse, 39 for default foreground color, 30 to
              37 for foreground colors, 90 to 97 for 16-color mode foreground colors,  38;5;0  to
              38;5;255  for  88-color  and  256-color  modes  foreground  colors,  49 for default
              background color, 40 to 47 for background colors, 100  to  107  for  16-color  mode
              background  colors,  and  48;5;0  to  48;5;255  for  88-color  and  256-color modes
              background colors.

       LC_ALL, LC_COLLATE, LANG
              These variables specify the locale for the LC_COLLATE  category,  which  determines
              the collating sequence used to interpret range expressions like [a-z].

       LC_ALL, LC_CTYPE, LANG
              These  variables specify the locale for the LC_CTYPE category, which determines the
              type of characters, e.g., which characters are whitespace.

       LC_ALL, LC_MESSAGES, LANG
              These variables specify the locale for the LC_MESSAGES category,  which  determines
              the  language  that  grep  uses  for  messages.  The default C locale uses American
              English messages.

       POSIXLY_CORRECT
              If set, grep behaves as POSIX.2 requires; otherwise, grep behaves more  like  other
              GNU programs.  POSIX.2 requires that options that follow file names must be treated
              as file names; by default, such options are permuted to the front  of  the  operand
              list  and are treated as options.  Also, POSIX.2 requires that unrecognized options
              be diagnosed as “illegal”, but since they  are  not  really  against  the  law  the
              default   is   to  diagnose  them  as  “invalid”.   POSIXLY_CORRECT  also  disables
              _N_GNU_nonoption_argv_flags_, described below.

       _N_GNU_nonoption_argv_flags_
              (Here N is grep's numeric process ID.)  If the ith character  of  this  environment
              variable's  value  is  1,  do not consider the ith operand of grep to be an option,
              even if it appears to be one.  A shell can put this variable in the environment for
              each  command  it  runs,  specifying  which  operands  are the results of file name
              wildcard expansion and therefore should not be treated as options.   This  behavior
              is available only with the GNU C library, and only when POSIXLY_CORRECT is not set.

EXIT STATUS

       The  exit  status  is  0  if  selected  lines  are found, and 1 if not found.  If an error
       occurred the exit status is 2.  (Note: POSIX error handling code should check for  '2'  or
       greater.)

COPYRIGHT

       Copyright 1998-2000, 2002, 2005-2011 Free Software Foundation, Inc.

       This  is  free software; see the source for copying conditions.  There is NO warranty; not
       even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

BUGS

   Reporting Bugs
       Email  bug  reports  to  <bug-grep@gnu.org>,  a   mailing   list   whose   web   page   is
       <http://lists.gnu.org/mailman/listinfo/bug-grep>.   grep's Savannah bug tracker is located
       at <http://savannah.gnu.org/bugs/?group=grep>.

   Known Bugs
       Large repetition counts in the {n,m} construct may cause grep to use lots of  memory.   In
       addition,  certain  other  obscure regular expressions require exponential time and space,
       and may cause grep to run out of memory.

       Back-references are very slow, and may require exponential time.

SEE ALSO

   Regular Manual Pages
       awk(1), cmp(1), diff(1), find(1), gzip(1), perl(1), sed(1), sort(1),  xargs(1),  zgrep(1),
       mmap(2), read(2), pcre(3), pcresyntax(3), pcrepattern(3), terminfo(5), glob(7), regex(7).

   POSIX Programmer's Manual Page
       grep(1p).

   TeXinfo Documentation
       The  full  documentation for grep is maintained as a TeXinfo manual.  If the info and grep
       programs are properly installed at your site, the command

              info grep

       should give you access to the complete manual.

NOTES

       GNU's not Unix, but Unix is a beast; its plural form is Unixen.