|
PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
SORT(1P) POSIX Programmer's Manual SORT(1P)
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 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.
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 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:
field_start[type][,field_end[type]]
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.
LC_COLLATE
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.
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
LC_NUMERIC
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.
Default.
Unless the −o or −c options are in effect, the standard output shall
contain the sorted input.
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.
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:
field_number[.first_character]
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:
field_number[.last_character]
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.
Default.
The following sections are informative.
The default value for −t, <blank>, has different properties from, for
example, −t"<space>". If a line contains:
<space><space>foo
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 │ empty │ empty │
│ 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
y<tab>b
x<space>a
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
Atlanta|425022|Georgia
Birmingham|284413|Alabama
Columbia|100385|South Carolina
eof
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 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
separator):
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 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.
None.
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)
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 http://www.unix.org/online.html .
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
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 SORT(1P)
Pages that refer to this page: comm(1p), join(1p), uniq(1p)