sort(1p) — Linux manual page


SORT(1P)                  POSIX Programmer's Manual                 SORT(1P)

PROLOG         top

       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.

NAME         top

       sort — sort, merge, or sequence check text files

SYNOPSIS         top

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

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

DESCRIPTION         top

       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 output.

        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.

OPTIONS         top

       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

       −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

       −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

       −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 applies.

       −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.

OPERANDS         top

       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.

STDIN         top

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

INPUT FILES         top

       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

       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

       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.



STDOUT         top

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

STDERR         top

       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 status.

OUTPUT FILES         top

       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


       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


       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

       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.)

EXIT STATUS         top

       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>:

                    │Field Default      −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 sorted:

           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.

EXAMPLES         top

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

               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

RATIONALE         top

       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

       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

       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 implementations.

       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.



SEE ALSO         top

       comm(1p), join(1p), uniq(1p)

       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(3p)

COPYRIGHT         top

       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 .

IEEE/The Open Group                 2013                            SORT(1P)

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