@table @samp
+@item -k @var{pos1}[,@var{pos2}]
+@itemx --key=@var{pos1}[,@var{pos2}]
+@opindex -k
+@opindex --key
+@cindex sort field
+Specify a sort field that consists of the part of the line between
+@var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
+omitted), @emph{inclusive}. Fields and character positions are numbered
+starting with 1. So to sort on the second field, you'd use
+@option{--key=2,2} (@option{-k 2,2}). See below for more examples.
+
@item -o @var{output-file}
@itemx --output=@var{output-file}
@opindex -o
That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
not considered to be part of either the field preceding or the field
-following. But note that sort fields that extend to the end of the line,
-as @option{-k 2}, or sort fields consisting of a range, as @option{-k 2,3},
+following, so with @samp{sort @w{-t " "}} the same input line has
+three fields: an empty field, @samp{foo}, and @samp{bar}.
+However, fields that extend to the end of the line,
+as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
retain the field separators present between the endpoints of the range.
To specify a zero byte (@acronym{ASCII} @sc{nul} (Null) character) as
equal. For the @option{--check} (@option{-c}) option,
check that no pair of consecutive lines compares equal.
-@item -k @var{pos1}[,@var{pos2}]
-@itemx --key=@var{pos1}[,@var{pos2}]
-@opindex -k
-@opindex --key
-@cindex sort field
-Specify a sort field that consists of the part of the line between
-@var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
-omitted), @emph{inclusive}. Fields and character positions are numbered
-starting with 1. So to sort on the second field, you'd use
-@option{--key=2,2} (@option{-k 2,2}). See below for more examples.
-
@item -z
@itemx --zero-terminated
@opindex -z
from the beginning of the field. In a start position, an omitted
@samp{.@var{c}} stands for the field's first character. In an end
position, an omitted or zero @samp{.@var{c}} stands for the field's
-last character. If the
+last character. If the start field falls after the end of the line
+or after the end field, the field is empty. If the
@option{-b} option was specified, the @samp{.@var{c}} part of a field
specification is counted from the first nonblank character of the field.
attached to either or both of the start and
end positions of a field specification, and if it is inherited
from the global options it will be attached to both.
-Keys may span multiple fields.
+If input lines can contain leading or adjacent blanks and @option{-t}
+is not used, then @option{-k} is typically combined with @option{-b},
+@option{-g}, @option{-M}, or @option{-n}; otherwise the varying
+numbers of leading blanks in fields can cause confusing results.
+
+Keys can span multiple fields.
On older systems, @command{sort} supports an obsolete origin-zero
syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
Sort in descending (reverse) numeric order.
@example
-sort -nr
+sort -n -r
@end example
@item
-Sort alphabetically, omitting the first and second fields.
+Sort alphabetically, omitting the first and second fields
+and the blanks at the start of the third field.
This uses a single key composed of the characters beginning
-at the start of field three and extending to the end of each line.
+at the start of the first nonblank character in field three
+and extending to the end of each line.
@example
-sort -k 3
+sort -k 3b
@end example
@item
sort -t : -k 2,2n -k 5.3,5.4
@end example
-Note that if you had written @option{-k 2} instead of @option{-k 2,2}
+Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
@command{sort} would have used all characters beginning in the second field
and extending to the end of the line as the primary @emph{numeric}
key. For the large majority of applications, treating keys spanning
@item
Sort the password file on the fifth field and ignore any
leading blanks. Sort lines with equal values in field five
-on the numeric user ID in field three.
+on the numeric user ID in field three. Fields are separated
+by @samp{:}.
@example
sort -t : -k 5b,5 -k 3,3n /etc/passwd
+sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
+sort -t : -b -k 5,5 -k 3,3n /etc/passwd
@end example
-An alternative is to use the global numeric modifier @option{-n}.
+These three commands have equivalent effect. The first specifies that
+the first key's start position ignores leading blanks and the second
+key is sorted numerically. The other two commands rely on global
+options being inherited by sort keys that lack modifiers. The inheritance
+works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
+equivalent, as the location of a field-end lacking a @samp{.@var{c}}
+character position is not affected by whether initial blanks are
+skipped.
+
+@item
+Sort a set of log files, primarily by IPv4 address and secondarily by
+time stamp. If two lines' primary and secondary keys are identical,
+output the lines in the same order that they were input. The log
+files contain lines that look like this:
@example
-sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
+4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
+211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
+@end example
+
+Fields are separated by exactly one space. Sort IPv4 addresses
+lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
+because 61 is less than 129.
+
+@example
+sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
+sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
@end example
+This example cannot be done with a single @command{sort} invocation,
+since IPv4 address components are separated by @samp{.} while dates
+come just after a space. So it is broken down into two invocations of
+@command{sort}: the first sorts by time stamp and the second by IPv4
+address. The time stamp is sorted by year, then month, then day, and
+finally by hour-minute-second field, using @option{-k} to isolate each
+field. Except for hour-minute-second there's no need to specify the
+end of each key field, since the @samp{n} and @samp{M} modifiers sort
+based on leading prefixes that cannot cross field boundaries. The
+IPv4 addresses are sorted lexicographically. The second sort uses
+@samp{-s} so that ties in the primary key are broken by the secondary
+key; the first sort uses @samp{-s} so that the combination of the two
+sorts is stable.
+
@item
Generate a tags file in case-insensitive sorted order.
that pathnames that contain Line Feed characters will not get broken up
by the sort operation.
-Finally, to ignore both leading and trailing blanks, you
-could have applied the @samp{b} modifier to the field-end specifier
-for the first key,
-
-@example
-sort -t : -n -k 5b,5b -k 3,3 /etc/passwd
-@end example
-
-or by using the global @option{-b} modifier instead of @option{-n}
-and an explicit @samp{n} with the second key specifier.
-
-@example
-sort -t : -b -k 5,5 -k 3,3n /etc/passwd
-@end example
-
@c This example is a bit contrived and needs more explanation.
@c @item
@c Sort records separated by an arbitrary string by using a pipe to convert
@smallexample
$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' |
-> tr -s '[ ]' '\012' | sort | uniq -c | sort -nr
+> tr -s '[ ]' '\012' | sort | uniq -c | sort -n -r
@print{} 156 the
@print{} 60 a
@print{} 58 to
projects / thirdparty / coreutils.git / commitdiff
