Remove consecutive duplicate lines with sed

remove_duplicate_lines_sed.sh

# from https://www.linuxquestions.org/questions/programming-9/removing-duplicate-lines-with-sed-276169/
# $!N
#    if not in the last line, append the next line of input 
#        pattern space (no duplicates): line1\nline2
#        stdout: null
#
# /^\(.*\)\n\1$/
#    does the pattern space (eg. line1\nline2) contains duplicate lines (eg. line1 == line2)? 
#
# /<REGEX>/!P
#    if the pattern space does not contain duplicate lines, print the pattern space up to \n
#        pattern space: line1\nline2
#        stdout: line1
#    else
#        pattern space: line1\nline2
#        stdout: null  
# D
#    delete up to \n and restart the loop with line2
#        pattern space when restarting cycle: line2
sed -n '$!N; /^\(.*\)\n\1$/!P; D' <file>