+.Nm uniq
+utility reads an input file or the standard input
+comparing adjacent
+lines, and writes one copy of each input line on the output.
+The second and succeeding copies of repeated adjacent input
+lines are not written.
+Repeated lines in the input are not detected if they are
+not adjacent, so it is important to
+.Xr sort 1
+the files first.
+.Pp
+The following options are available:
+.Bl -tag -width Ds
+.It Fl c
+Precede each output line with a count of the number
+of times the line occurred in the input. For example:
+.Bd -literal -offset indent
+duplicate_count line_number
+.Ed
+.Pp
+where the duplicate count is a blank padded field of
+up to four digits followed by a space.
+.It Fl d
+Suppress the writing of lines that are not repeated
+in the input.
+.It Fl f Ar fields
+Ignore the first fields on each input line when
+doing comparisons, where fields is a positive
+decimal integer.
+A field is a string of non-blank
+characters separated from adjacent fields
+by blanks.
+.It Fl s Ar chars
+Ignore the first chars characters when doing
+comparisons, where chars is a positive decimal
+integer.
+If specified in conjunction with the
+.Fl f
+option, the first chars characters after the first
+fields fields will be ignored.
+.It Fl u
+Suppress the writing of lines that are repeated in
+the input.
+.It Fl Ns Ar n
+(Deprecated; replaced by
+.Fl f ) .
+Ignore the first n
+fields on each input line when doing comparisons,
+where n is a number.
+A field is a string of non-blank
+characters separated from adjacent fields
+by blanks.
+.It Cm \&\(pl Ns Ar n
+(Deprecated; replaced by
+.Fl s ) .
+Ignore the first
+.Ar m
+characters when doing comparisons, where
+.Ar m
+is a
+number.
+.El
+.Pp
+The following operands are available:
+.Bl -tag -width output_filex
+.It Ar input_file
+A pathname of the input file.
+If the
+.Ar input_file
+operand is not specified, the standard input is
+used.
+.It Ar output_file
+A pathname of the output file.
+This name shall
+always be different from
+.Ar input_file.
+If the
+.Ar output_file
+operand is not specified, the standard
+output is used. If
+.Ar output_file
+is created and an error occurs or a sugnal is caught the
+.Ar output_file
+is not removed.
+.El
+.\" .Pp
+.\" The following environment variables affect the execution of
+.\" uniq:
+.\" .Tl Em LC_CTYPE
+.\" The locale for character classification, used to
+.\" determine the characters constituting a blank in
+.\" the current locale.
+.Pp