+.TH SORT 1L \" -*- nroff -*-
+.SH NAME
+sort \- sort lines of text files
+.SH SYNOPSIS
+.B sort
+[\-cmus] [\-t separator] [\-o output-file] [\-bdfiMnr] [+POS1 [\-POS2]]
+[\-k POS1[,POS2]] [file...]
+.SH DESCRIPTION
+This manual page
+documents the GNU version of
+.BR sort .
+.B sort
+sorts, merges, or compares all the lines from the given files, or the standard
+input if no files are given. A file name of `-' means standard input.
+By default,
+.B sort
+writes the results to the standard output.
+.PP
+.B sort
+has three modes of operation: sort (the default), merge, and check for
+sortedness. The following options change the operation mode:
+.TP
+.I \-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.
+.TP
+.I \-m
+Merge the given files by sorting them as a group. Each input file
+should already be individually sorted. It always works to sort
+instead of merge; merging is provided because it is faster, in the
+case where it works.
+.PP
+A pair of lines is compared as follows:
+if any key fields have been specified,
+.B 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.
+.PP
+If any of the global options
+.I Mbdfinr
+are given but no key fields are
+specified,
+.B sort
+compares the entire lines according to the global options.
+.PP
+Finally, as a last resort when all keys compare equal
+(or if no ordering options were specified at all),
+.B sort
+compares the lines byte by byte in machine collating sequence. The
+.I \-s
+option disables this last resort comparison, producing a stable sort.
+.PP
+GNU
+.B sort
+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
+.B sort
+silently supplies one. In some cases, such as exactly what the
+.I \-b
+and
+.I \-f
+options do, BSD and System V
+.B sort
+programs produce different output; GNU
+.B sort
+follows the POSIX behavior, which is usually like the System V behavior.
+.PP
+If the environment variable TMPDIR is set,
+.B sort
+uses it as the directory in which to put temporary files instead of
+the default, /tmp.
+.PP
+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.
+.TP
+.I \-b
+Ignore leading blanks when finding sort keys in each line.
+.TP
+.I \-d
+Sort in `dictionary order': ignore all characters except letters,
+digits and blanks when sorting.
+.TP
+.I \-f
+Fold lower case characters into the equivalent upper case characters
+when sorting so that, for example, `b' is sorted the same way `B' is.
+.TP
+.I \-i
+Ignore characters outside the ASCII range 040-0176 (inclusive) when sorting.
+.TP
+.I \-M
+An initial string, consisting of any amount of white space, followed
+by three letters abbreviating a month name, is folded to lower case
+and compared in the order `jan' < `feb' < ... < `dec.' Invalid names
+compare low to valid names. This option implies
+.IR \-b .
+.TP
+.I \-n
+Compare according to arithmetic value an initial numeric string
+consisting of optional white space, an optional \- sign, and zero or
+more digits, optionally followed by a decimal point and zero or more
+digits. This option implies
+.IR \-b .
+.TP
+.I \-r
+Reverse the result of comparison, so that lines with greater key
+values appear earlier in the output instead of later.
+.PP
+Other options are:
+.TP
+.I "\-o output-file"
+Write output to
+.I output-file
+instead of to the standard output. If
+.I output-file
+is one of the input files,
+.B sort
+copies it to a temporary file before sorting and writing the output to
+.IR output-file .
+.TP
+.I "\-t separator"
+Use character
+.I 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 to say,
+given the input line ` foo bar',
+.B 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 it.
+.TP
+.I \-u
+For the default case or the
+.I \-m
+option, only output the first of a sequence of lines that compare
+equal. For the
+.I \-c
+option, check that no pair of consecutive lines compares equal.
+.TP
+.I "+POS1 [\-POS2]"
+Specify a field within each line to use as a sorting key. The field
+consists of the portion of the line starting at POS1 and up to (but
+not including) POS2 (or to the end of the line if POS2 is not given).
+The fields and character positions are numbered starting with 0.
+.TP
+.I "\-k POS1[,POS2]"
+An alternate syntax for specifying sorting keys.
+The fields and character positions are numbered starting with 1.
+.PP
+A position has the form \fIf\fP.\fIc\fP, where \fIf\fP is the number
+of the field to use and \fIc\fP is the number of the first character
+from the beginning of the field (for \fI+pos\fP) or from the end of
+the previous field (for \fI\-pos\fP). The .\fIc\fP part of a position
+may be omitted in which case it is taken to be the first character in
+the field. If the
+.I \-b
+option has been given, the .\fIc\fP part of a field specification is
+counted from the first nonblank character of the field (for
+\fI+pos\fP) or from the first nonblank character following the
+previous field (for \fI\-pos\fP).
+.PP
+A \fI+pos\fP or \fI-pos\fP argument may also have any of the option
+letters
+.I Mbdfinr
+appended to it, in which case the global ordering options are not used
+for that particular field. The
+.I \-b
+option may be independently attached to either or both of the
+\fI+pos\fP and \fI\-pos\fP parts of a field specification, and if it
+is inherited from the global options it will be attached to both.
+If a
+.I \-n
+or
+.I \-M
+option is used, thus implying a
+.I \-b
+option, the
+.I \-b
+option is taken to apply to both the \fI+pos\fP and the \fI\-pos\fP
+parts of a key specification. Keys may span multiple fields.
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