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(sort invocation): Mention -k earlier, so

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that the options are in alphabetical order.  Describe how -b works
more-accurately; this involves fixing some examples, too.  Mention
what happens if the start field falls after an end field or after
a line end.  Warn about using -k without -b, -g, -M, -n, or -t.
Add an example of how to sort IPv4 addresses and Apache Common
Log Format dates.  Remove a duplicate example.
(Putting the tools together): Use separate options rather
than agglomerating them.
This commit is contained in:
Jim Meyering
2004-04-26 15:37:48 +00:00
parent 30ea278e1b
commit c20e6668c8
1 changed files with 74 additions and 39 deletions
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113
doc/coreutils.texi
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@@ -3248,6 +3248,17 @@ Other options are:
@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
@@ -3313,8 +3324,10 @@ string between a non-blank character and a blank character.
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
@@ -3344,17 +3357,6 @@ Normally, output only the first of a sequence of lines that compare
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
@@ -3385,7 +3387,8 @@ of the field to use and @var{c} is the number of the first character
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.
@@ -3395,7 +3398,12 @@ for that particular field. The @option{-b} option may be independently
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.
@@ -3410,16 +3418,18 @@ Here are some examples to illustrate various combinations of options.
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
@@ -3431,7 +3441,7 @@ Use @samp{:} as the field delimiter.
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
@@ -3447,18 +3457,58 @@ field-end part of the key specifier.
@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.
@@ -3470,21 +3520,6 @@ The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
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
@@ -12972,7 +13007,7 @@ The final pipeline looks like this:
@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