Remove duplicate adjacent lines from sorted file1, sending one copy of each line to file2 (or to standard output). Often used as a filter. Specify only one of -d or -u. See also comm and sort.
Ignore first n fields of a line. Fields are separated by spaces or by tabs.
Ignore first n characters of a field.
Print each line once, prefixing number of instances.
Print duplicate lines once but no unique lines.
Print all duplicate lines. -D takes no delimiter method. The delimiter method method takes one of the values none (default), prepend, or separate. Blank lines are used as the delimiter.
Ignore case differences when checking for duplicates.
Print only unique lines (no copy of duplicate entries is kept).
Compare only first n characters per line (beginning after skipped fields and characters).
Print a help message and then exit.
Print version information and then exit.
Send one copy of each line from list to output file list.new:
uniq list list.new
Show which names appear more than once:
sort names | uniq -d