bash remove duplicate lines from a file

# Basic syntax:
sort input_file | uniq --unique
# Sort the file first because uniq requires a sorted file to work. Uniq
# then eliminates all duplicated lines in the file, keeping one instance
# of each duplicated line

# Note, this doesn't return only non-duplicated lines. It returns
# unique instances of all lines, whether or not they are duplicated

# Note, if you want to return only one instance of all lines but see
# the number of repetitions for each line, run:
sort input_file | uniq -csort -u .txt