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       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.


       sort — sort, merge, or sequence check text files


       sort [−m] [−o output] [−bdfinru] [−t char] [−k keydef]... [file...]

       sort [−c|−C] [−bdfinru] [−t char] [−k keydef] [file]


       The sort utility shall perform one of the following functions:

        1. Sort  lines  of  all  the  named  files together and write the result to the specified

        2. Merge lines of all the named (presorted) files together and write the  result  to  the
           specified output.

        3. Check that a single input file is correctly presorted.

       Comparisons shall be based on one or more sort keys extracted from each line of input (or,
       if no sort keys are specified, the entire line up to, but not including,  the  terminating
       <newline>), and shall be performed using the collating sequence of the current locale.


       The  sort  utility  shall  conform to the Base Definitions volume of POSIX.1‐2008, Section
       12.2, Utility Syntax Guidelines, except for Guideline 9, and the −k keydef  option  should
       follow  the  −b,  −d, −f, −i, −n, and −r options. In addition, '+' may be recognized as an
       option delimiter as well as '−'.

       The following options shall be supported:

       −c        Check that the single input file is ordered as specified by  the  arguments  and
                 the  collating  sequence  of  the  current  locale.  Output shall not be sent to
                 standard output. The exit code  shall  indicate  whether  or  not  disorder  was
                 detected  or  an  error  occurred. If disorder (or, with −u, a duplicate key) is
                 detected, a warning message shall be sent to standard error indicating where the
                 disorder or duplicate key was found.

       −C        Same as −c, except that a warning message shall not be sent to standard error if
                 disorder or, with −u, a duplicate key is detected.

       −m        Merge only; the input file shall be assumed to be already sorted.

       −o output Specify the name of an output file to be used instead of  the  standard  output.
                 This file can be the same as one of the input files.

       −u        Unique:  suppress  all  but one in each set of lines having equal keys.  If used
                 with the −c option, check that there  are  no  lines  with  duplicate  keys,  in
                 addition to checking that the input file is sorted.

       The  following  options  shall  override the default ordering rules. When ordering options
       appear independent of any key field specifications, the  requested  field  ordering  rules
       shall  be applied globally to all sort keys. When attached to a specific key (see −k), the
       specified ordering options shall override all global ordering options for that key.

       −d        Specify that only <blank> characters and alphanumeric characters,  according  to
                 the  current  setting  of  LC_CTYPE,  shall  be  significant in comparisons. The
                 behavior is undefined for a sort key to which −i or −n also applies.

       −f        Consider all lowercase characters that have uppercase equivalents, according  to
                 the current setting of LC_CTYPE, to be the uppercase equivalent for the purposes
                 of comparison.

       −i        Ignore all characters that are non-printable, according to the  current  setting
                 of  LC_CTYPE.   The  behavior  is  undefined  for  a  sort key for which −n also

       −n        Restrict the sort key to an  initial  numeric  string,  consisting  of  optional
                 <blank>  characters,  optional  minus-sign,  and  zero  or  more  digits with an
                 optional radix character and thousands separators (as  defined  in  the  current
                 locale),  which shall be sorted by arithmetic value. An empty digit string shall
                 be treated as zero. Leading zeros and signs on zeros shall not affect ordering.

       −r        Reverse the sense of comparisons.

       The treatment of field separators can be altered using the options:

       −b        Ignore leading <blank> characters  when  determining  the  starting  and  ending
                 positions  of  a  restricted  sort key. If the −b option is specified before the
                 first −k option, it shall be applied to all −k options. Otherwise, the −b option
                 can  be  attached  independently  to  each  −k  field_start or field_end option-
                 argument (see below).

       −t char   Use char as the field separator character; char shall not be  considered  to  be
                 part  of a field (although it can be included in a sort key). Each occurrence of
                 char shall be significant (for example, <char><char> delimits an  empty  field).
                 If  −t  is  not  specified,  <blank>  characters  shall be used as default field
                 separators; each maximal non-empty sequence of <blank> characters that follows a
                 non-<blank> shall be a field separator.

       Sort keys can be specified using the options:

       −k keydef The  keydef  argument  is  a restricted sort key field definition. The format of
                 this definition is:


                 where field_start and field_end define a key field restricted to  a  portion  of
                 the line (see the EXTENDED DESCRIPTION section), and type is a modifier from the
                 list of characters 'b', 'd', 'f', 'i', 'n', 'r'.  The 'b' modifier shall  behave
                 like  the  −b  option,  but  shall apply only to the field_start or field_end to
                 which it is attached. The other modifiers shall behave  like  the  corresponding
                 options,  but shall apply only to the key field to which they are attached; they
                 shall have this effect if specified with field_start, field_end, or both. If any
                 modifier  is  attached to a field_start or to a field_end, no option shall apply
                 to either. Implementations shall support at least nine  occurrences  of  the  −k
                 option,  which  shall  be  significant in command line order. If no −k option is
                 specified, a default sort key of the entire line shall be used.

                 When there are multiple key fields, later keys shall be compared only after  all
                 earlier  keys  compare equal. Except when the −u option is specified, lines that
                 otherwise compare equal shall be ordered as if none of the options −d,  −f,  −i,
                 −n,  or  −k  were present (but with −r still in effect, if it was specified) and
                 with all bytes in the lines significant to the comparison. The  order  in  which
                 lines that still compare equal are written is unspecified.


       The following operand shall be supported:

       file      A  pathname  of a file to be sorted, merged, or checked. If no file operands are
                 specified, or if a file operand is '−', the standard input shall be used.


       The standard input shall be used only if no file operands are  specified,  or  if  a  file
       operand is '−'.  See the INPUT FILES section.


       The input files shall be text files, except that the sort utility shall add a <newline> to
       the end of a file ending with an incomplete last line.


       The following environment variables shall affect the execution of sort:

       LANG      Provide a default value for the internationalization variables that are unset or
                 null.   (See   the   Base  Definitions  volume  of  POSIX.1‐2008,  Section  8.2,
                 Internationalization  Variables  for  the  precedence  of   internationalization
                 variables used to determine the values of locale categories.)

       LC_ALL    If  set  to  a  non-empty  string  value,  override  the values of all the other
                 internationalization variables.

                 Determine the locale for ordering rules.

       LC_CTYPE  Determine the locale for the interpretation of sequences of bytes of  text  data
                 as  characters  (for example, single-byte as opposed to multi-byte characters in
                 arguments and input files) and the behavior of character classification for  the
                 −b, −d, −f, −i, and −n options.

                 Determine  the  locale  that should be used to affect the format and contents of
                 diagnostic messages written to standard error.

                 Determine the locale for the definition of the  radix  character  and  thousands
                 separator for the −n option.

       NLSPATH   Determine the location of message catalogs for the processing of LC_MESSAGES.




       Unless  the  −o  or −c options are in effect, the standard output shall contain the sorted


       The standard error shall be used  for  diagnostic  messages.  When  −c  is  specified,  if
       disorder  is  detected  (or  if  −u  is also specified and a duplicate key is detected), a
       message shall be written to the standard error which identifies the input  line  at  which
       disorder  (or  a  duplicate  key)  was  detected.  A  warning  message about correcting an
       incomplete last line of an input file may be generated, but need not affect the final exit


       If the −o option is in effect, the sorted input shall be written to the file output.


       The notation:

           −k field_start[type][,field_end[type]]

       shall  define  a  key  field  that  begins at field_start and ends at field_end inclusive,
       unless field_start falls beyond the end of the line or after field_end, in which case  the
       key field is empty. A missing field_end shall mean the last character of the line.

       A  field  comprises a maximal sequence of non-separating characters and, in the absence of
       option −t, any preceding field separator.

       The field_start portion of the keydef option-argument shall have the form:


       Fields and characters within fields shall be numbered starting with 1.   The  field_number
       and  first_character  pieces,  interpreted as positive decimal integers, shall specify the
       first character to be used as part of a sort key. If .first_character is omitted, it shall
       refer to the first character of the field.

       The field_end portion of the keydef option-argument shall have the form:


       The  field_number  shall be as described above for field_start.  The last_character piece,
       interpreted as a non-negative decimal integer, shall specify the last character to be used
       as  part  of  the  sort  key.  If  last_character  evaluates to zero or .last_character is
       omitted, it shall refer to the last character of the field specified by field_number.

       If the −b option or b type modifier is in effect,  characters  within  a  field  shall  be
       counted  from  the  first  non-<blank>  in  the  field.  (This  shall  apply separately to
       first_character and last_character.)


       The following exit values shall be returned:

        0    All input files were output successfully, or −c was specified and the input file was
             correctly sorted.

        1    Under  the  −c  option,  the  file was not ordered as specified, or if the −c and −u
             options were both specified, two input lines were found with equal keys.

       >1    An error occurred.



       The following sections are informative.


       The  default  value  for  −t,  <blank>,  has  different  properties  from,  for   example,
       −t"<space>". If a line contains:


       the  following  treatment  would  occur with default separation as opposed to specifically
       selecting a <space>:

                               │FieldDefault−t "<space>" │
                               │  1   │ <space><space>foo │ empty        │
                               │  2   │ emptyempty        │
                               │  3   │ empty             │ foo          │
       The leading field separator itself is included in  a  field  when  −t  is  not  used.  For
       example,  this  command  returns  an  exit  status  of zero, meaning the input was already

           sort −c −k 2 <<eof

       (assuming that a <tab> precedes the <space> in the current collating sequence). The  field
       separator is not included in a field when it is explicitly set via −t.  This is historical
       practice and allows usage such as:

           sort −t "|" −k 2n <<eof
           Columbia|100385|South Carolina

       where the second field can be correctly sorted numerically  without  regard  to  the  non-
       numeric field separator.

       The  wording  in the OPTIONS section clarifies that the −b, −d, −f, −i, −n, and −r options
       have to come before the first sort key specified if they are  intended  to  apply  to  all
       specified  keys. The way it is described in this volume of POSIX.1‐2008 matches historical
       practice, not historical documentation.  The results are unspecified if these options  are
       specified after a −k option.

       The  −f  option  might  not  work  as  expected in locales where there is not a one-to-one
       mapping between an uppercase and a lowercase letter.


        1. The following command sorts the contents of infile with the second field as  the  sort

               sort −k 2,2 infile

        2. The  following  command  sorts, in reverse order, the contents of infile1 and infile2,
           placing the output in outfile and using the second character of the  second  field  as
           the  sort  key  (assuming  that  the  first character of the second field is the field

               sort −r −o outfile −k 2.2,2.2 infile1 infile2

        3. The following command sorts the contents of  infile1  and  infile2  using  the  second
           non-<blank> of the second field as the sort key:

               sort −k 2.2b,2.2b infile1 infile2

        4. The  following command prints the System V password file (user database) sorted by the
           numeric user ID (the third <colon>-separated field):

               sort −t : −k 3,3n /etc/passwd

        5. The following command prints the lines of the already sorted file infile,  suppressing
           all but one occurrence of lines having the same third field:

               sort −um −k 3.1,3.0 infile


       Examples  in some historical documentation state that options −um with one input file keep
       the first in each set of lines with  equal  keys.  This  behavior  was  deemed  to  be  an
       implementation artifact and was not standardized.

       The −z option was omitted; it is not standard practice on most systems and is inconsistent
       with using sort to sort several files individually and then merge them together. The  text
       concerning −z in historical documentation appeared to require implementations to determine
       the proper buffer length during the sort phase of operation, but not during the merge.

       The −y option was omitted because of non-portability. The −M option, present in System  V,
       was omitted because of non-portability in international usage.

       An  undocumented  −T  option  exists  in  some  implementations.  It  is used to specify a
       directory for intermediate files. Implementations are encouraged to support the use of the
       TMPDIR environment variable instead of adding an option to support this functionality.

       The  −k option was added to satisfy two objections. First, the zero-based counting used by
       sort is not consistent with other utility conventions. Second,  it  did  not  meet  syntax
       guideline requirements.

       Historical  documentation indicates that ``setting −n implies −b''.  The description of −n
       already states that optional leading <blank>s are tolerated in doing the comparison. If −b
       is  enabled,  rather  than implied, by −n, this has unusual side-effects. When a character
       offset is used in a column of numbers (for example, to sort modulo 100),  that  offset  is
       measured  relative  to  the  most  significant  digit,  not  to  the column.  Based upon a
       recommendation from the author of the original sort utility, the −b implication  has  been
       omitted  from  this  volume  of  POSIX.1‐2008,  and  an application wishing to achieve the
       previously mentioned side-effects has to code the −b flag explicitly.

       Earlier versions of this  standard  allowed  the  −o  option  to  appear  after  operands.
       Historical  practice allowed all options to be interspersed with operands. This version of
       the standard allows implementations  to  accept  options  after  operands  but  conforming
       applications should not use this form.

       Earlier  versions  of  this  standard  also allowed the number and +number options. These
       options  are  no  longer  specified  by  POSIX.1‐2008  but  may   be   present   in   some

       Historical  implementations produced a message on standard error when −c was specified and
       disorder was detected, and when −c and −u were specified and a duplicate key was detected.
       An earlier version of this standard contained wording that did not make it clear that this
       message was allowed and some implementations removed this message to  be  sure  that  they
       conformed  to  the  standard's  requirements. Confronted with this difference in behavior,
       interactive users that wanted to be sure that they got visual  feedback  instead  of  just
       exit code 1 could have used a command like:

           sort −c file || echo disorder

       whether  or not the sort utility provided a message in this case. But, it was not easy for
       a user to find where the disorder or duplicate key occurred on implementations that do not
       produce  a  message, especially when some parts of the input line were not part of the key
       and when one or more of the −b, −d, −f, −i, −n, or r options  or  keydef  type  modifiers
       were  in  use.  POSIX.1‐2008  requires a message to be produced in this case. POSIX.1‐2008
       also contains the −C option giving users the ability to choose either behavior.

       When  a  disorder  or  duplicate  is  found  when  the  −c  option  is   specified,   some
       implementations print a message containing the first line that is out of order or contains
       a duplicate key; others print a message specifying the line number of the offending  line.
       This standard allows either type of message.




       comm, join, uniq

       The  Base  Definitions  volume  of POSIX.1‐2008, Chapter 8, Environment Variables, Section
       12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2008, toupper()


       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2013  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013  by  the
       Institute  of  Electrical  and  Electronics  Engineers,  Inc and The Open Group.  (This is
       POSIX.1-2008 with the  2013  Technical  Corrigendum  1  applied.)  In  the  event  of  any
       discrepancy  between  this  version and the original IEEE and The Open Group Standard, the
       original IEEE and The Open Group Standard is the referee document. The  original  Standard
       can be obtained online at .

       Any  typographical  or  formatting errors that appear in this page are most likely to have
       been introduced during the conversion of the source files to man page  format.  To  report
       such errors, see .