uniq command in linux shell

uniq command is used to find only unique lines in a file.
uniq <file-name> 
# This command will display only unique lines in the file. 
# Note that only adjacent duplicate lines are removed. To remove all duplicates,
# you can sort the contents of file and then pipe the output to uniq command.
uniq -c <file-name> 
# Here -c stands for count. It displays the count of occurences of each line.
uniq -d <file-name>
# Here -d stands for duplicate. It displays the duplicate lines once for each set of 
# duplicate occurence.
uniq -D <file-name> 
# It displays all occurrences of duplicate lines.
uniq -u <file-name> 
# It displays only unique line.
uniq -c -w 4 <file-name> 
# Use first 4 chars for checking uniqueness
uniq -D -s 4 <file-name> 
# avoid comparing first 4 chars
uniq -D -f 4 <file-name> 
# avoid compaing first 4 words

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