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Manual Pages  — SORT


sort – sort or merge records (lines) of text and binary files



sort [-bcCdfghiRMmnrsuVz] [-k amp; field1 [, field2]][-S memsize] [-T dir] [-t char] [-o output] [file ...]
sort -help
sort -version


The sort utility sorts text and binary files by lines. A line is a record separated from the subsequent record by a newline (default) or NUL \0 character (-z option). A record can contain any printable or unprintable characters. Comparisons are based on one or more sort keys extracted from each line of input, and are performed lexicographically, according to the current locale's collating rules and the specified command-line options that can tune the actual sorting behavior. By default, if keys are not given, sort uses entire lines for comparison.

The command line options are as follows:
-c -, -check -, -C -, -check=silent|quiet
  Check that the single input file is sorted. If the file is not sorted, sort produces the appropriate error messages and exits with code 1, otherwise returns 0. If -C or -check=silent is specified, sort produces no output. This is a "silent" version of -c.
-m -, -merge
  Merge only. The input files are assumed to be pre-sorted. If they are not sorted the output order is undefined.
-o output , -output -= output
  Print the output to the output file instead of the standard output.
-S size , -buffer-size -= size
  Use size for the maximum size of the memory buffer. Size modifiers %,b,K,M,G,T,P,E,Z,Y can be used. If a memory limit is not explicitly specified, sort takes up to about 90% of available memory. If the file size is too big to fit into the memory buffer, the temporary disk files are used to perform the sorting.
-T dir , -temporary-directory -= dir
  Store temporary files in the directory dir. The default path is the value of the environment variable TMPDIR or /var/tmp if TMPDIR is not defined.
-u -, -unique
  Unique keys. Suppress all lines that have a key that is equal to an already processed one. This option, similarly to -s, implies a stable sort. If used with -c or -C, sort also checks that there are no lines with duplicate keys.
  Stable sort. This option maintains the original record order of records that have an equal key. This is a non-standard feature, but it is widely accepted and used.
  Print the version and silently exits.
  Print the help text and silently exits.

The following options override the default ordering rules. When ordering options appear independently of key field specifications, they apply globally to all sort keys. When attached to a specific key (see -k), the ordering options override all global ordering options for the key they are attached to.
-b -, -ignore-leading-blanks
  Ignore leading blank characters when comparing lines.
-d -, -dictionary-order
  Consider only blank spaces and alphanumeric characters in comparisons.
-f -, -ignore-case
  Convert all lowercase characters to their uppercase equivalent before comparison, that is, perform case-independent sorting.
-g -, -general-numeric-sort -, -sort=general-numeric
  Sort by general numerical value. As opposed to -n, this option handles general floating points. It has a more permissive format than that allowed by -n but it has a significant performance drawback.
-h -, -human-numeric-sort -, -sort=human-numeric
  Sort by numerical value, but take into account the SI suffix, if present. Sort first by numeric sign (negative, zero, or positive); then by SI suffix (either empty, or `k' or `K', or one of `MGTPEZY', in that order); and finally by numeric value. The SI suffix must immediately follow the number. For example, '12345K' sorts before '1M', because M is "larger" than K. This sort option is useful for sorting the output of a single invocation of 'df' command with -h or -H options (human-readable).
-i -, -ignore-nonprinting
  Ignore all non-printable characters.
-M -, -month-sort -, -sort=month
  Sort by month abbreviations. Unknown strings are considered smaller than the month names.
-n -, -numeric-sort -, -sort=numeric
  Sort fields numerically by arithmetic value. Fields are supposed to have optional blanks in the beginning, an optional minus sign, zero or more digits (including decimal point and possible thousand separators).
-R -, -random-sort -, -sort=random
  Sort by a random order. This is a random permutation of the inputs except that the equal keys sort together. It is implemented by hashing the input keys and sorting the hash values. The hash function is chosen randomly. The hash function is randomized by /dev/random content, or by file content if it is specified by -random-source. Even if multiple sort fields are specified, the same random hash function is used for all of them.
-r -, -reverse
  Sort in reverse order.
-V -, -version-sort
  Sort version numbers. The input lines are treated as file names in form PREFIX VERSION SUFFIX, where SUFFIX matches the regular expression "(.([A-Za-z~][A-Za-z0-9~]*)?)*". The files are compared by their prefixes and versions (leading zeros are ignored in version numbers, see example below). If an input string does not match the pattern, then it is compared using the byte compare function. All string comparisons are performed in C locale, the locale environment setting is ignored.
$ ls sort* | sort -V

The treatment of field separators can be altered using these options:
-b -, -ignore-leading-blanks
  Ignore leading blank space when determining the start and end of a restricted sort key (see -k). If -b is specified before the first -k option, it applies globally to all key specifications. Otherwise, -b can be attached independently to each field argument of the key specifications. -b.
-k field1[,field2], -key -= field1[,field2] Define a restricted sort key that has the starting position field1, and optional ending position field2 of a key field. The -k option may be specified multiple times, in which case subsequent keys are compared when earlier keys compare equal. The -k option replaces the obsolete options +pos1 and pos2, but the old notation is also supported.
-t char , -field-separator -= char
  Use char as a field separator character. The initial char is not considered to be part of a field when determining key offsets. Each occurrence of char is significant (for example, "charchar" delimits an empty field). If -t is not specified, the default field separator is a sequence of blank space characters, and consecutive blank spaces do not delimit an empty field, however, the initial blank space is considered part of a field when determining key offsets. To use NUL as field separator, use -t \0.
-z -, -zero-terminated
  Use NUL as record separator. By default, records in the files are supposed to be separated by the newline characters. With this option, NUL (\0) is used as a record separator character.

Other options:
-batch-size -= num
  Specify maximum number of files that can be opened by sort at once. This option affects behavior when having many input files or using temporary files. The default value is 16.
-compress-program -= PROGRAM
  Use PROGRAM to compress temporary files. PROGRAM must compress standard input to standard output, when called without arguments. When called with argument -d it must decompress standard input to standard output. If PROGRAM fails, sort must exit with error. An example of PROGRAM that can be used here is bzip2.
-random-source -= filename
  In random sort, the file content is used as the source of the 'seed' data for the hash function choice. Two invocations of random sort with the same seed data will use the same hash function and will produce the same result if the input is also identical. By default, file /dev/random is used.
  Print some extra information about the sorting process to the standard output.
-files0-from -= filename
  Take the input file list from the file filename. The file names must be separated by NUL (like the output produced by the command "find ... -print0").
  Try to use radix sort, if the sort specifications allow. The radix sort can only be used for trivial locales (C and POSIX), and it cannot be used for numeric or month sort. Radix sort is very fast and stable.
  Use mergesort. This is a universal algorithm that can always be used, but it is not always the fastest.
  Try to use quick sort, if the sort specifications allow. This sort algorithm cannot be used with -u and -s.
  Try to use heap sort, if the sort specifications allow. This sort algorithm cannot be used with -u and -s.
  Try to use file memory mapping system call. It may increase speed in some cases.

The following operands are available:
file The 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 is used.

A field is defined as a maximal sequence of characters other than the field separator and record separator (newline by default). Initial blank spaces are included in the field unless -b has been specified; the first blank space of a sequence of blank spaces acts as the field separator and is included in the field (unless -t is specified). For example, all blank spaces at the beginning of a line are considered to be part of the first field.

Fields are specified by the -k amp; field1 [, field2]command-line option. If field2 is missing, the end of the key defaults to the end of the line.

The arguments field1 and field2 have the form m.n (m,n > 0) and can be followed by one or more of the modifiers b, d, f, i, n, g, M and r, which correspond to the options discussed above. When b is specified it applies only to field1 or field2 where it is specified while the rest of the modifiers apply to the whole key field regardless if they are specified only with field1 or field2 or both. A field1 position specified by m.n is interpreted as the nth character from the beginning of the mth field. A missing amp;.n in field1 means ‘amp;.1’, indicating the first character of the mth field; if the -b option is in effect, n is counted from the first non-blank character in the mth field; mamp;.1b refers to the first non-blank character in the mth field. 1amp;. n refers to the nth character from the beginning of the line; if n is greater than the length of the line, the field is taken to be empty.

nth positions are always counted from the field beginning, even if the field is shorter than the number of specified positions. Thus, the key can really start from a position in a subsequent field.

A field2 position specified by m.n is interpreted as the nth character (including separators) from the beginning of the mth field. A missing amp;.n indicates the last character of the mth field; m = amp;0 designates the end of a line. Thus the option -k v.x,w.y is synonymous with the obsolete option +v-amp;1.x-amp;1 w-amp;1.y; when y is omitted, -k v.x,w is synonymous with +v-amp;1.x-amp;1 wamp;.0. The obsolete +pos1 pos2 option is still supported, except for wamp;.0b, which has no -k equivalent.


  Locale settings to be used to determine the collation for sorting records.
  Locale settings to be used to case conversion and classification of characters, that is, which characters are considered whitespaces, etc.
  Locale settings that determine the language of output messages that sort prints out.
  Locale settings that determine the number format used in numeric sort.
  Locale settings that determine the month format used in month sort.
  Locale settings that override all of the above locale settings. This environment variable can be used to set all these settings to the same value at once.
LANG Used as a last resort to determine different kinds of locale-specific behavior if neither the respective environment variable, nor LC_ALL are set.
  Path to NLS catalogs.
  Path to the directory in which temporary files will be stored. Note that TMPDIR may be overridden by the -T option.
  If defined -t will not override the locale numeric symbols, that is, thousand separators and decimal separators. By default, if we specify -t with the same symbol as the thousand separator or decimal point, the symbol will be treated as the field separator. Older behavior was less definite; the symbol was treated as both field separator and numeric separator, simultaneously. This environment variable enables the old behavior.


  Temporary files.
  Default seed file for the random sort.


The sort utility shall exit with one of the following values:

0 Successfully sorted the input files or if used with -c or -C, the input file already met the sorting criteria.
1 On disorder (or non-uniqueness) with the -c or -C options.
2 An error occurred.


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


The sort utility is compliant with the IEEE Std 1003.1-2008 ("POSIX.1") specification.

The flags [-ghRMSsTVz] are extensions to the POSIX specification.

All long options are extensions to the specification, some of them are provided for compatibility with GNU versions and some of them are own extensions.

The old key notations +pos1 and pos2 come from older versions of sort and are still supported but their use is highly discouraged.


A sort command first appeared in AT&T v3 .


Gabor Kovesdan <Mt gabor@FreeBSD.org>,

Oleg Moskalenko <Mt mom040267@gmail.com>


This implementation of sort has no limits on input line length (other than imposed by available memory) or any restrictions on bytes allowed within lines.

The performance depends highly on locale settings, efficient choice of sort keys and key complexity. The fastest sort is with locale C, on whole lines, with option -s. In general, locale C is the fastest, then single-byte locales follow and multi-byte locales as the slowest but the correct collation order is always respected. As for the key specification, the simpler to process the lines the faster the search will be.

When sorting by arithmetic value, using -n results in much better performance than -g so its use is encouraged whenever possible.

SORT (1) March 19, 2015

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