uniq - remove duplicate lines from a sorted file

Liunx version BDS Mac OS X (darwin)
uniq [option]... [input [output]]

Ignore all but one of successive identical lines from input (or standard input), writing to output (or standard output).

-u
--unique		 output only unique lines, (supressing lines with multiple occurances)
-d
--repeated 		output duplicate lines, i.e. not lines with only 1 occurance
-D
--all-repeated[=dm]		 output all duplicate lines
delimit-method : dm={none(default),prepend,separate}
Delimiting is done with blank lines.
-f
--skip-fields=n		 A field is delimited by whitespace
Fields are skipped before chars.
-s
--skip-chars=n		 for compare
-w
--check-chars=n		 compare no more than n characters in lines
-i
--ignore-case
-c
--count		 prefix output lines by the number of occurrences
--help
--version 

cat 00
11
11
2
3
4
44
44
5 
 
  uniq 00
11
2
3
4
44
5 

 uniq -c 00
      2 11
      1 2
      1 3
      1 4
      2 44
      1 5 

cat 00
11
11
2
3
4
44
44
5 

 uniq -u 00
2
3
4
5 

cat 00
11
11
2
3
4
44
44
5 

  uniq -D 00
11
11
44
44

AUTHOR Written by Richard Stallman and David MacKenzie. Copyright © 2002 Free Software Foundation, Inc.
uniq (coreutils) 4.5.3 October 2003 UNIQ(1) tersified by Dennis German

BSD Mac OS X (darwin)

uniq [-c | -d | -u] [-i] [-f n] [-s n] [input [output]]

reads the input comparing adjacent lines and writes each unique line to the output.

If input is a single dash (-) or absent, the standard input is read.
Standard output is default used for output.

Only duplicate adjacent lines are recognized, so it may be necessary to sort the file(s) first.

-d Duplicates Only are output
-u Unique lines only are output , i.e. lines with more than one adjacent occurance are NOT output
-c count is prefixed to each output line
-f nIgnore the first n fields in each input line when doing comparisons.
A field is a string of non-blank characters separated from adjacent fields by blanks.
Counting begins with 1, i.e., the first field is 1.
-s n Skip the first n characters in each input line when doing comparisons.
with -f, the first n characters after the first n fields will be skipped.
Counting begins with 1, i.e., the first character is 1.

When skipping Characters or Fields, outputting Duplicates only the first line with duplicate fields is output.

Example: 

input    uniq -f1   output
    xxx 21            xxx 21
    yyy 21
    zzz 23
-i Ignore case

examples

> cat ffff

11
11
2
3
4
44
44
5 

 > uniq ffff

11
2
3
4
44
5 
 

> uniq -d ffff
11
44


> uniq -u ffff

2
3
4
5 
 

> uniq -c ffff
   1 
   2 11
   1 2
   1 3
   1 4
   2 44
   1 5 
   1

ENVIRONMENT

The LANG, LC_ALL, LC_COLLATE and LC_CTYPE environment variables affect the execution as described in environ.

EXIT STATUS

exits 0 on success, and >0 if an error occurs.