GNU Info
(textutils.info)sort invocation
`sort': Sort text files
=======================
`sort' sorts, merges, or compares all the lines from the given
files, or standard input if none are given or for a FILE of `-'. By
default, `sort' writes the results to standard output. Synopsis:
sort [OPTION]... [FILE]...
`sort' has three modes of operation: sort (the default), merge, and
check for sortedness. The following options change the operation mode:
`-c'
Check whether the given files are already sorted: if they are not
all sorted, print an error message and exit with a status of 1.
Otherwise, exit successfully.
`-m'
Merge the given files by sorting them as a group. Each input file
must always be individually sorted. It always works to sort
instead of merge; merging is provided because it is faster, in the
case where it works.
A pair of lines is compared as follows: if any key fields have been
specified, `sort' compares each pair of fields, in the order specified
on the command line, according to the associated ordering options,
until a difference is found or no fields are left. Unless otherwise
specified, all comparisons use the character collating sequence
specified by the `LC_COLLATE' locale.
If any of the global options `Mbdfinr' are given but no key fields
are specified, `sort' compares the entire lines according to the global
options.
Finally, as a last resort when all keys compare equal (or if no
ordering options were specified at all), `sort' compares the entire
lines. The last resort comparison honors the `-r' global option. The
`-s' (stable) option disables this last-resort comparison so that lines
in which all fields compare equal are left in their original relative
order. If no fields or global options are specified, `-s' has no
effect.
GNU `sort' (as specified for all GNU utilities) has no limits on
input line length or restrictions on bytes allowed within lines. In
addition, if the final byte of an input file is not a newline, GNU
`sort' silently supplies one. A line's trailing newline is part of the
line for comparison purposes; for example, with no options in an ASCII
locale, a line starting with a tab sorts before an empty line because
tab precedes newline in the ASCII collating sequence.
Upon any error, `sort' exits with a status of `2'.
If the environment variable `TMPDIR' is set, `sort' uses its value
as the directory for temporary files instead of `/tmp'. The `-T
TEMPDIR' option in turn overrides the environment variable.
The following options affect the ordering of output lines. They may
be specified globally or as part of a specific key field. If no key
fields are specified, global options apply to comparison of entire
lines; otherwise the global options are inherited by key fields that do
not specify any special options of their own. The `-b', `-d', `-f' and
`-i' options classify characters according to the `LC_CTYPE' locale.
`-b'
Ignore leading blanks when finding sort keys in each line.
`-d'
Sort in "phone directory" order: ignore all characters except
letters, digits and blanks when sorting.
`-f'
Fold lowercase characters into the equivalent uppercase characters
when sorting so that, for example, `b' and `B' sort as equal.
`-g'
Sort numerically, using the standard C function `strtod' to convert
a prefix of each line to a double-precision floating point number.
This allows floating point numbers to be specified in scientific
notation, like `1.0e-34' and `10e100'. Do not report overflow,
underflow, or conversion errors. Use the following collating
sequence:
* Lines that do not start with numbers (all considered to be
equal).
* NaNs ("Not a Number" values, in IEEE floating point
arithmetic) in a consistent but machine-dependent order.
* Minus infinity.
* Finite numbers in ascending numeric order (with -0 and +0
equal).
* Plus infinity.
Use this option only if there is no alternative; it is much slower
than `-n' and it can lose information when converting to floating
point.
`-i'
Ignore unprintable characters.
`-M'
An initial string, consisting of any amount of whitespace, followed
by a month name abbreviation, is folded to UPPER case and compared
in the order `JAN' < `FEB' < ... < `DEC'. Invalid names compare
low to valid names. The `LC_TIME' locale determines the month
spellings.
`-n'
Sort numerically: the number begins each line; specifically, it
consists of optional whitespace, an optional `-' sign, and zero or
more digits possibly separated by thousands separators, optionally
followed by a radix character and zero or more digits. The
`LC_NUMERIC' locale specifies the radix character and thousands
separator.
`sort -n' uses what might be considered an unconventional method
to compare strings representing floating point numbers. Rather
than first converting each string to the C `double' type and then
comparing those values, sort aligns the radix characters in the two
strings and compares the strings a character at a time. One
benefit of using this approach is its speed. In practice this is
much more efficient than performing the two corresponding
string-to-double (or even string-to-integer) conversions and then
comparing doubles. In addition, there is no corresponding loss of
precision. Converting each string to `double' before comparison
would limit precision to about 16 digits on most systems.
Neither a leading `+' nor exponential notation is recognized. To
compare such strings numerically, use the `-g' option.
`-r'
Reverse the result of comparison, so that lines with greater key
values appear earlier in the output instead of later.
Other options are:
`-o OUTPUT-FILE'
Write output to OUTPUT-FILE instead of standard output. If
OUTPUT-FILE is one of the input files, `sort' copies it to a
temporary file before sorting and writing the output to
OUTPUT-FILE.
`-t SEPARATOR'
Use character SEPARATOR as the field separator when finding the
sort keys in each line. By default, fields are separated by the
empty string between a non-whitespace character and a whitespace
character. That is, given the input line ` foo bar', `sort'
breaks it into fields ` foo' and ` bar'. The field separator is
not considered to be part of either the field preceding or the
field following.
`-u'
For the default case or the `-m' option, only output the first of
a sequence of lines that compare equal. For the `-c' option,
check that no pair of consecutive lines compares equal.
`-k POS1[,POS2]'
The recommended, POSIX, option for specifying a sort field. The
field consists of the part of the line between POS1 and POS2 (or
the end of the line, if POS2 is omitted), _inclusive_. Fields and
character positions are numbered starting with 1. So to sort on
the second field, you'd use `-k 2,2' See below for more examples.
`-z'
Treat the input as a set of lines, each terminated by a zero byte
(ASCII NUL (Null) character) instead of an ASCII LF (Line Feed).
This option can be useful in conjunction with `perl -0' or `find
-print0' and `xargs -0' which do the same in order to reliably
handle arbitrary pathnames (even those which contain Line Feed
characters.)
`+POS1[-POS2]'
The obsolete, traditional option for specifying a sort field. The
field consists of the line between POS1 and up to but _not
including_ POS2 (or the end of the line if POS2 is omitted).
Fields and character positions are numbered starting with 0. See
below.
In addition, when GNU `sort' is invoked with exactly one argument,
options `--help' and `--version' are recognized. Note: Common
options.
Historical (BSD and System V) implementations of `sort' have
differed in their interpretation of some options, particularly `-b',
`-f', and `-n'. GNU sort follows the POSIX behavior, which is usually
(but not always!) like the System V behavior. According to POSIX, `-n'
no longer implies `-b'. For consistency, `-M' has been changed in the
same way. This may affect the meaning of character positions in field
specifications in obscure cases. The only fix is to add an explicit
`-b'.
A position in a sort field specified with the `-k' or `+' option has
the form `F.C', where F is the number of the field to use and C is the
number of the first character from the beginning of the field (for
`+POS') or from the end of the previous field (for `-POS'). If the `.C'
is omitted, it is taken to be the first character in the field. If the
`-b' option was specified, the `.C' part of a field specification is
counted from the first nonblank character of the field (for `+POS') or
from the first nonblank character following the previous field (for
`-POS').
A sort key option may also have any of the option letters `Mbdfinr'
appended to it, in which case the global ordering options are not used
for that particular field. The `-b' option may be independently
attached to either or both of the `+POS' and `-POS' parts of a field
specification, and if it is inherited from the global options it will
be attached to both. Keys may span multiple fields.
Here are some examples to illustrate various combinations of options.
In them, the POSIX `-k' option is used to specify sort keys rather than
the obsolete `+POS1-POS2' syntax.
* Sort in descending (reverse) numeric order.
sort -nr
Sort alphabetically, omitting the first and second fields. This
uses a single key composed of the characters beginning at the
start of field three and extending to the end of each line.
sort -k3
* Sort numerically on the second field and resolve ties by sorting
alphabetically on the third and fourth characters of field five.
Use `:' as the field delimiter.
sort -t : -k 2,2n -k 5.3,5.4
Note that if you had written `-k 2' instead of `-k 2,2' `sort'
would have used all characters beginning in the second field and
extending to the end of the line as the primary _numeric_ key.
For the large majority of applications, treating keys spanning
more than one field as numeric will not do what you expect.
Also note that the `n' modifier was applied to the field-end
specifier for the first key. It would have been equivalent to
specify `-k 2n,2' or `-k 2n,2n'. All modifiers except `b' apply
to the associated _field_, regardless of whether the modifier
character is attached to the field-start and/or the field-end part
of the key specifier.
* Sort the password file on the fifth field and ignore any leading
white space. Sort lines with equal values in field five on the
numeric user ID in field three.
sort -t : -k 5b,5 -k 3,3n /etc/passwd
An alternative is to use the global numeric modifier `-n'.
sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
* Generate a tags file in case insensitive sorted order.
find src -type f -print0 | sort -t / -z -f | xargs -0 etags --append
The use of `-print0', `-z', and `-0' in this case mean that
pathnames that contain Line Feed characters will not get broken up
by the sort operation.
Finally, to ignore both leading and trailing white space, you
could have applied the `b' modifier to the field-end specifier for
the first key,
sort -t : -n -k 5b,5b -k 3,3 /etc/passwd
or by using the global `-b' modifier instead of `-n' and an
explicit `n' with the second key specifier.
sort -t : -b -k 5,5 -k 3,3n /etc/passwd
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