DeDup is a Java command-line utilty for removing duplicate
lines in text files.
The dedup process compares adjacent lines only. It does not
sort first. The comparison is case-sensitive. It removes
adjacent indentical lines. It replaces the original file, so
do a backup first.  You can dedup 1 to N files in one
execution, just put their names on the command line.
DeDup deletes blank lines from both the beginning and end of
the file. It also deletes trailing blanks from each line. It
also cleans up line terminators \r \n \r\n and converts them
all to platform standard.  If the file is already deduped,
it does not change the date.
Use it with:
java com.mindprod.dedup.DeDup  myfile.txt anotherfile.txt  yetanotherfile.txt
or
java.exe -jar dedup.jar myfile.txt anotherfile.txt  yetanotherfile.txt
or, if you have the jar association set up, even even
dedup.jar myfile.txt anotherfile.txt  yetanotherfile.txt
It can handle a list of files, or an os-expanded wildcard.
It does not -s to process subdirectories or the use of
directory names to process entire directories.
Why the four little green men icon.  Three are duplicates.
The second (marked with a red X) would be eliminated because
it is adjactent to an indentical copy.  The rest are left as
is, just as DeDup functions.